SPC Aug 15, 2018 2000 UTC Day 1 Convective Outlook

30 minutes 7 seconds ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Wed Aug 15 2018 Valid 152000Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NEBRASKA AND SOUTHERN SOUTH DAKOTA... ...SUMMARY... The main severe-storm threat area remains across parts of the north-central Plains region this afternoon and evening, with large hail and severe wind gusts possible. ...20Z Update... The only substantial change with this update has been to remove the Marginal/Slight risk from parts of southern/central SD based on latest observational trends. The prospect for substantial re-destabilization behind ongoing convection across north-central NE and south-central SD appears limited. Additional thunderstorms posing an isolated large hail and damaging wind threat will likely form along an east-west oriented outflow boundary across western/central NE this afternoon. For more information on the short-term severe risk across this region, see Mesoscale Discussion 1297. ..Gleason.. 08/15/2018 .PREV DISCUSSION... /ISSUED 1119 AM CDT Wed Aug 15 2018/ ...SD/NE... Water vapor loop shows a vigorous shortwave trough tracking eastward across northeast WY. This system will move into SD/NE this afternoon, with strengthening winds aloft and height falls spreading across the region. Thunderstorms are ongoing this morning along the SD/NE border, which will likely leave an outflow boundary that could provide the focus for re-development later today. 12z CAM solutions are consistent in the development of intense storms by late afternoon, tracking east-southeastward across the SLGT risk area into the evening. Forecast soundings show rather steep mid level lapse rates and MLCAPE of 1500-2000 J/kg, along with strong deep-layer shear. This will promote the development of a few supercells capable of very large hail, damaging winds, and perhaps a tornado or two. ...Eastern CO/NM and the TX Panhandle... Strong heating is occurring early today over southeast CO and northeast NM, with weak upslope low-level flow. Ample mid/upper level moisture combined with moderate CAPE values, will result in scattered thunderstorms over this region by mid-afternoon. These storms will spread eastward across the MRGL risk area during the evening. The strongest cells will be capable of gusty/damaging winds and hail. ...OK into IN/KY... Multiple clusters of thunderstorms are ongoing this morning from the Ozarks into the lower Ohio Valley. Pockets of heating around these clusters will allow for the development of afternoon thunderstorms. Wind fields aloft are marginal for convective organization, but high surface dewpoint values and rather strong winds in the 1-3km layer suggest a few storms could occasionally produce gusty/damaging winds. ...Northeast states... Fast northwest flow aloft is present today across eastern Canada, and will spread into parts of NY and New England later today. Multiple progressive shortwave troughs embedded in the flow will help initiate scattered thunderstorms that track into the MRGL risk region this afternoon and evening. Relatively steep lapse rates and MLCAPE values of 1500+ J/kg may result in hail and/or gusty/damaging winds in a few of the stronger cells. Forecast coverage intense cells suggests that MRGL designation is appropriate today, but some potential exists for an upgrade later today if coverage exceeds expectations. Read more

SPC MD 1297

41 minutes 56 seconds ago
MD 1297 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR CENTRAL NEBRASKA
Mesoscale Discussion 1297 NWS Storm Prediction Center Norman OK 0252 PM CDT Wed Aug 15 2018 Areas affected...Central Nebraska Concerning...Severe potential...Watch possible Valid 151952Z - 152215Z Probability of Watch Issuance...40 percent SUMMARY...Scattered strong to potentially severe storms will be possible within the next few hours. Straight line damaging winds and large hail will be the primary threats with this activity. Convective trends are being monitored for the issuance of a Severe Thunderstorm Watch. DISCUSSION...A leading convection-trailing stratiform MCS is currently traversing the north-central Nebraska/south-central South Dakota border, with weaker convection back-building along its southwestern flank, and an outflow boundary sagging south and west of a line extending from ONL to TIF. This MCS and associated outflow boundary are progressing east-southeastward into an ambient environment characterized by 1000-1500 J/kg MLCAPE (driven mainly by 7.5+ C/km lapse rates and dewpoints into the 60s), 35 knots of effective bulk shear, and strong deep-layer ascent due in part to a mid-level vort max propagating eastward from western South Dakota. Low-level speed/directional shear is weak across the discussion area, suggesting that most storms will be outflow dominant in nature, and with a 1200 m sub-cloud layer present, damaging gusty winds will be a concern. The modest deep-layer shear also suggests that some mid-level updraft organization/rotation will be possible, prompting a large hail threat. As convection has been rather slow to re-develop across the discussion area, and given a marginal ambient kinematic/thermodynamic environment present, convective trends will continue to be monitored regarding the issuance of a Severe Thunderstorm Watch ..Squitieri/Hart.. 08/15/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...OAX...GID...LBF... LAT...LON 42040164 42000147 41930108 41930069 42010042 42130031 42310015 42519996 42669976 42789953 42899918 42949886 42779835 42589820 42219807 41899807 41759802 41339810 40749834 40419854 40259928 40459987 41000043 41360096 41700130 41880146 42040174 42040164 Read more

SPC MD 1296

43 minutes 57 seconds ago
MD 1296 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR SOUTHERN IL...SOUTHWEST KY...FAR SOUTHWEST IN
Mesoscale Discussion 1296 NWS Storm Prediction Center Norman OK 0250 PM CDT Wed Aug 15 2018 Areas affected...Southern IL...Southwest KY...Far Southwest IN Concerning...Severe potential...Watch unlikely Valid 151950Z - 152145Z Probability of Watch Issuance...20 percent SUMMARY...Threat for locally damaging wind gusts exists ahead of the ongoing thunderstorm cluster across southern IL. DISCUSSION...Recent radar imagery has shown increased forward propagation over the last half hour or so as the stronger storm moving across far southeast MO becomes more outflow dominant and interacts with the weaker cells ahead of it. Motion of this thunderstorm is also favorably aligned with the low to mid-level flow across the region. Recent KPAH and KVWX VAD data indicates 30 kt southwest winds at 1 km. In additional to contributing to increased potential for damaging wind gusts, this stronger low to mid-level flow is also increasing low-level vertical shear and overall updraft strength. Low-level lapse rates are more favorable farther south, but recent mesoanalysis still suggests a narrow area of 7.0+ deg C per km lapse rates immediately ahead of the surging thunderstorm cluster. All of these factors result in increased probabilities for damaging wind gusts immediately downstream of the ongoing cluster. Eastern extent of threat will likely be limited by cooler temperatures and weaker instability in southern IN. Limited spatial extent of the threat tempers the need for watch. ..Mosier/Hart.. 08/15/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LMK...PAH... LAT...LON 36778889 36868931 37198948 37688927 38028846 38028734 37548704 36968736 36778889 Read more

SPC Day 2 Fire Weather Outlook

1 hour 3 minutes ago
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Wed Aug 15 2018 Valid 161200Z - 171200Z Expanded the IsoDryT line to cover most of central Idaho as latest guidance suggests mid-level moisture will increase and isolated storms are possible Thursday afternoon and evening. PWAT values will be quite limited (0.6 to 0.7 inch range), so any storms which form will likely be dry. Storm coverage would definitely support a scattered delineation across northeast Oregon, but storm organization and PWAT values around 0.8 to 1.0 inches will favor wet storms. Have kept this area in the IsoDryT as storm motion and antecedent very dry fuels will still support some fire starts, but the chance for new large fires may be somewhat limited by the organized storm structure and the potential for wetting rains. ..Bentley.. 08/15/2018 .PREV DISCUSSION... /ISSUED 0143 AM CDT Wed Aug 15 2018/ ...Synopsis... The upper-level ridge axis will shift to the east as a shortwave trough approaches the Pacific Northwest on D2/Thursday. At the surface, strong heating across the Columbia Basin will lead to a thermally induced surface pressure trough which, with terrain enhancement, will lead to surface winds of 15-20 mph within parts of the Columbia River Gorge. Afternoon RH values will fall to 10-20%. With critically dry fuels in place, elevated fire weather conditions are expected. Isolated dry thunderstorms will again be possible from the Harney Basin into much of the Great Basin. PWAT values will be higher than Wednesday, with values 0.6-1.0 inches. However, with the approach of the mid-level wave, storm motions will also see an increase leading to a mix of both wet and dry storms. Due to the very dry fuels across the region, lightning ignitions will likely be efficient. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC MD 1295

1 hour 29 minutes ago
MD 1295 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTHERN NY...NORTHERN VT
Mesoscale Discussion 1295 NWS Storm Prediction Center Norman OK 0204 PM CDT Wed Aug 15 2018 Areas affected...Northern NY...Northern VT Concerning...Severe potential...Watch unlikely Valid 151904Z - 152130Z Probability of Watch Issuance...20 percent SUMMARY...Thunderstorms will remain possible for the next several hours. A few of these storms may produce isolated damaging wind gusts and/or hail. DISCUSSION...Strong heating amidst the moist airmass across the region is contributing to moderate instability ahead of a shortwave trough and associated cold front. Continued forcing for ascent along the boundary and attendant to the shortwave trough will provide the impetus for additional thunderstorms, although overall coverage is not expected to be particularly widespread. At the same time, enhanced mid-level flow attendant to the shortwave trough will spread eastward into the region, resulting in an increase in vertical shear. This increase in vertical shear supports the potential for more organized updrafts and a resultant threat for damaging wind gusts and/or hail. Limited severe coverage is expected to temper the need for a watch. ..Mosier/Hart.. 08/15/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BTV...ALY...BGM...BUF... LAT...LON 44237609 44477542 44627444 44697351 44607210 44157209 43557332 43137440 42787606 43147722 43747669 44237609 Read more

SPC Aug 15, 2018 1730 UTC Day 2 Convective Outlook

3 hours 5 minutes ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1226 PM CDT Wed Aug 15 2018 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL PLAINS... ...SUMMARY... Isolated strong to severe storms will be possible Thursday over parts of the central Plains into the mid Mississippi Valley. Other strong storms may occur from the lower Mississippi Valley into the Tennessee and Ohio Valleys. ...Synopsis... A mid/upper-level trough over the OH Valley Thursday morning will move northeastward across the Lower Great Lakes and southern Ontario through the period. An upstream upper trough/low across the northern/central Plains will develop southeastward to the mid MS Valley by Thursday evening. Farther west, an upper trough will overspread parts of the Pacific Northwest as upper ridging remains prominent over much of the western states. At the surface, a weak cold front should develop slowly southeastward across the OH Valley, with the trailing portion of this front becoming nearly stationary across the southern Plains. A weak secondary cold front will also advance southward across the central Plains through the day. ...Central Plains into the Mid MS Valley... A moist low-level airmass, with surface dewpoints generally in the mid to upper 60s, will reside across southeastern NE into eastern KS and western MO along and south of a weak cold front. Modestly steepened mid-level lapse rates will also encourage moderate instability to develop as diurnal heating occurs. Storms may be ongoing across eastern NE at the start of the period, but additional convective development will likely occur along the front by Thursday afternoon in northeastern KS and vicinity. Strengthening west-northwesterly mid-level flow and related effective bulk shear of 30-40 kt should allow for a mix of supercells and multicells across this region. Isolated large hail and damaging winds should be the primary threats. There will be some potential for one or more small clusters to continue southeastward into southeastern KS and western/central MO Thursday evening, with at least a marginal hail/wind threat persisting. ...OH/TN Valleys into the Lower MS Valley and Southern Plains... A belt of 30-40 kt low-level southwesterly flow will accompany the shortwave trough across the OH/TN Valleys through Thursday afternoon. However, winds are forecast to weaken with height at mid levels, which will tend to limit deep-layer shear and the potential for thunderstorms to become organized on more than a transient/isolated basis. Still, enough low-level flow coupled with pockets of instability that should develop along/ahead of morning convection will probably support some potential for isolated strong to locally damaging winds with multicells and short line segments developing northeastward across the OH/TN Valleys. Along the trailing portion of a weak front across OK/AR into the Mid-South, shear is forecast to remain weak, although a front will probably act as a focus for renewed convective development Thursday afternoon. The airmass across this region is forecast to become at least moderately unstable, with MLCAPE of 2000-2500 J/kg probable. Convective evolution remains uncertain across OK/AR in particular, with some guidance suggesting a bowing cluster with strong/damaging winds may develop over eastern OK into western AR in the afternoon. However, given the weak low and mid-level flow expected, will maintain Marginal risk across this region. ...Central/Eastern OR... Mid-level south-southwesterly flow will likely increase into the 25-35 kt range across much of OR as an upper trough approaches from the west. Similar effective bulk shear values should encourage some updraft organization as thunderstorms develop along the Cascade crest and spread northeastward across parts of central/eastern OR Thursday afternoon and evening. Forecast soundings across this region show a deeply mixed boundary layer, and strong/gusty downdraft winds may occur. Limited low-level moisture and generally weak instability should keep the severe threat isolated/marginal. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 15% - Slight Hail: 15% - Slight ..Gleason.. 08/15/2018 Read more

SPC Aug 15, 2018 1730 UTC Day 2 Convective Outlook

3 hours 5 minutes ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1226 PM CDT Wed Aug 15 2018 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL PLAINS... ...SUMMARY... Isolated strong to severe storms will be possible Thursday over parts of the central Plains into the mid Mississippi Valley. Other strong storms may occur from the lower Mississippi Valley into the Tennessee and Ohio Valleys. ...Synopsis... A mid/upper-level trough over the OH Valley Thursday morning will move northeastward across the Lower Great Lakes and southern Ontario through the period. An upstream upper trough/low across the northern/central Plains will develop southeastward to the mid MS Valley by Thursday evening. Farther west, an upper trough will overspread parts of the Pacific Northwest as upper ridging remains prominent over much of the western states. At the surface, a weak cold front should develop slowly southeastward across the OH Valley, with the trailing portion of this front becoming nearly stationary across the southern Plains. A weak secondary cold front will also advance southward across the central Plains through the day. ...Central Plains into the Mid MS Valley... A moist low-level airmass, with surface dewpoints generally in the mid to upper 60s, will reside across southeastern NE into eastern KS and western MO along and south of a weak cold front. Modestly steepened mid-level lapse rates will also encourage moderate instability to develop as diurnal heating occurs. Storms may be ongoing across eastern NE at the start of the period, but additional convective development will likely occur along the front by Thursday afternoon in northeastern KS and vicinity. Strengthening west-northwesterly mid-level flow and related effective bulk shear of 30-40 kt should allow for a mix of supercells and multicells across this region. Isolated large hail and damaging winds should be the primary threats. There will be some potential for one or more small clusters to continue southeastward into southeastern KS and western/central MO Thursday evening, with at least a marginal hail/wind threat persisting. ...OH/TN Valleys into the Lower MS Valley and Southern Plains... A belt of 30-40 kt low-level southwesterly flow will accompany the shortwave trough across the OH/TN Valleys through Thursday afternoon. However, winds are forecast to weaken with height at mid levels, which will tend to limit deep-layer shear and the potential for thunderstorms to become organized on more than a transient/isolated basis. Still, enough low-level flow coupled with pockets of instability that should develop along/ahead of morning convection will probably support some potential for isolated strong to locally damaging winds with multicells and short line segments developing northeastward across the OH/TN Valleys. Along the trailing portion of a weak front across OK/AR into the Mid-South, shear is forecast to remain weak, although a front will probably act as a focus for renewed convective development Thursday afternoon. The airmass across this region is forecast to become at least moderately unstable, with MLCAPE of 2000-2500 J/kg probable. Convective evolution remains uncertain across OK/AR in particular, with some guidance suggesting a bowing cluster with strong/damaging winds may develop over eastern OK into western AR in the afternoon. However, given the weak low and mid-level flow expected, will maintain Marginal risk across this region. ...Central/Eastern OR... Mid-level south-southwesterly flow will likely increase into the 25-35 kt range across much of OR as an upper trough approaches from the west. Similar effective bulk shear values should encourage some updraft organization as thunderstorms develop along the Cascade crest and spread northeastward across parts of central/eastern OR Thursday afternoon and evening. Forecast soundings across this region show a deeply mixed boundary layer, and strong/gusty downdraft winds may occur. Limited low-level moisture and generally weak instability should keep the severe threat isolated/marginal. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 15% - Slight Hail: 15% - Slight ..Gleason.. 08/15/2018 Read more

SPC MD 1294

4 hours 7 minutes ago
MD 1294 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR MUCH OF ME...NORTHERN NH
Mesoscale Discussion 1294 NWS Storm Prediction Center Norman OK 1126 AM CDT Wed Aug 15 2018 Areas affected...Much of ME...Northern NH Concerning...Severe potential...Watch unlikely Valid 151626Z - 151830Z Probability of Watch Issuance...5 percent SUMMARY...Increasing thunderstorm coverage expected with isolated damaging wind gusts and/or hail possible. DISCUSSION...Airmass ahead of a shortwave trough moving through southern Quebec continues to destabilize amidst mid 60s dewpoints and ample daytime heating. Widely scattered convection has been observed thus far with storms struggling to maintain updrafts. As heating continues and the forcing for ascent increases, the expectation is for more overall thunderstorm coverage and persistence. Given the moderate instability (i.e. MLCAPE around 1500-2000 J/kg), a few stronger updrafts capable of damaging wind gusts and/or hail are possible. However, the overall severe potential will be mitigated somewhat by the presence of generally modest mid-level flow and resulting lack of strong vertical shear. ..Mosier/Hart.. 08/15/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...CAR...GYX...BTV... LAT...LON 46497014 47096958 47376903 47186802 45956787 45416767 44786827 44506882 44276953 44187051 44147117 44427167 45117144 45837028 46497014 Read more

SPC Aug 15, 2018 1630 UTC Day 1 Convective Outlook

4 hours 8 minutes ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1119 AM CDT Wed Aug 15 2018 Valid 151630Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTH DAKOTA AND NEBRASKA... ...SUMMARY... The main severe-storm threat area is over parts of the north-central Plains region this afternoon and evening, for large hail and severe gusts. ...SD/NE... Water vapor loop shows a vigorous shortwave trough tracking eastward across northeast WY. This system will move into SD/NE this afternoon, with strengthening winds aloft and height falls spreading across the region. Thunderstorms are ongoing this morning along the SD/NE border, which will likely leave an outflow boundary that could provide the focus for re-development later today. 12z CAM solutions are consistent in the development of intense storms by late afternoon, tracking east-southeastward across the SLGT risk area into the evening. Forecast soundings show rather steep mid level lapse rates and MLCAPE of 1500-2000 J/kg, along with strong deep-layer shear. This will promote the development of a few supercells capable of very large hail, damaging winds, and perhaps a tornado or two. ...Eastern CO/NM and the TX Panhandle... Strong heating is occurring early today over southeast CO and northeast NM, with weak upslope low-level flow. Ample mid/upper level moisture combined with moderate CAPE values, will result in scattered thunderstorms over this region by mid-afternoon. These storms will spread eastward across the MRGL risk area during the evening. The strongest cells will be capable of gusty/damaging winds and hail. ...OK into IN/KY... Multiple clusters of thunderstorms are ongoing this morning from the Ozarks into the lower Ohio Valley. Pockets of heating around these clusters will allow for the development of afternoon thunderstorms. Wind fields aloft are marginal for convective organization, but high surface dewpoint values and rather strong winds in the 1-3km layer suggest a few storms could occasionally produce gusty/damaging winds. ...Northeast states... Fast northwest flow aloft is present today across eastern Canada, and will spread into parts of NY and New England later today. Multiple progressive shortwave troughs embedded in the flow will help initiate scattered thunderstorms that track into the MRGL risk region this afternoon and evening. Relatively steep lapse rates and MLCAPE values of 1500+ J/kg may result in hail and/or gusty/damaging winds in a few of the stronger cells. Forecast coverage intense cells suggests that MRGL designation is appropriate today, but some potential exists for an upgrade later today if coverage exceeds expectations. ..Hart/Squitieri.. 08/15/2018 Read more

SPC Aug 15, 2018 1630 UTC Day 1 Convective Outlook

4 hours 8 minutes ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1119 AM CDT Wed Aug 15 2018 Valid 151630Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTH DAKOTA AND NEBRASKA... ...SUMMARY... The main severe-storm threat area is over parts of the north-central Plains region this afternoon and evening, for large hail and severe gusts. ...SD/NE... Water vapor loop shows a vigorous shortwave trough tracking eastward across northeast WY. This system will move into SD/NE this afternoon, with strengthening winds aloft and height falls spreading across the region. Thunderstorms are ongoing this morning along the SD/NE border, which will likely leave an outflow boundary that could provide the focus for re-development later today. 12z CAM solutions are consistent in the development of intense storms by late afternoon, tracking east-southeastward across the SLGT risk area into the evening. Forecast soundings show rather steep mid level lapse rates and MLCAPE of 1500-2000 J/kg, along with strong deep-layer shear. This will promote the development of a few supercells capable of very large hail, damaging winds, and perhaps a tornado or two. ...Eastern CO/NM and the TX Panhandle... Strong heating is occurring early today over southeast CO and northeast NM, with weak upslope low-level flow. Ample mid/upper level moisture combined with moderate CAPE values, will result in scattered thunderstorms over this region by mid-afternoon. These storms will spread eastward across the MRGL risk area during the evening. The strongest cells will be capable of gusty/damaging winds and hail. ...OK into IN/KY... Multiple clusters of thunderstorms are ongoing this morning from the Ozarks into the lower Ohio Valley. Pockets of heating around these clusters will allow for the development of afternoon thunderstorms. Wind fields aloft are marginal for convective organization, but high surface dewpoint values and rather strong winds in the 1-3km layer suggest a few storms could occasionally produce gusty/damaging winds. ...Northeast states... Fast northwest flow aloft is present today across eastern Canada, and will spread into parts of NY and New England later today. Multiple progressive shortwave troughs embedded in the flow will help initiate scattered thunderstorms that track into the MRGL risk region this afternoon and evening. Relatively steep lapse rates and MLCAPE values of 1500+ J/kg may result in hail and/or gusty/damaging winds in a few of the stronger cells. Forecast coverage intense cells suggests that MRGL designation is appropriate today, but some potential exists for an upgrade later today if coverage exceeds expectations. ..Hart/Squitieri.. 08/15/2018 Read more

SPC Aug 15, 2018 1630 UTC Day 1 Convective Outlook

4 hours 8 minutes ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1119 AM CDT Wed Aug 15 2018 Valid 151630Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTH DAKOTA AND NEBRASKA... ...SUMMARY... The main severe-storm threat area is over parts of the north-central Plains region this afternoon and evening, for large hail and severe gusts. ...SD/NE... Water vapor loop shows a vigorous shortwave trough tracking eastward across northeast WY. This system will move into SD/NE this afternoon, with strengthening winds aloft and height falls spreading across the region. Thunderstorms are ongoing this morning along the SD/NE border, which will likely leave an outflow boundary that could provide the focus for re-development later today. 12z CAM solutions are consistent in the development of intense storms by late afternoon, tracking east-southeastward across the SLGT risk area into the evening. Forecast soundings show rather steep mid level lapse rates and MLCAPE of 1500-2000 J/kg, along with strong deep-layer shear. This will promote the development of a few supercells capable of very large hail, damaging winds, and perhaps a tornado or two. ...Eastern CO/NM and the TX Panhandle... Strong heating is occurring early today over southeast CO and northeast NM, with weak upslope low-level flow. Ample mid/upper level moisture combined with moderate CAPE values, will result in scattered thunderstorms over this region by mid-afternoon. These storms will spread eastward across the MRGL risk area during the evening. The strongest cells will be capable of gusty/damaging winds and hail. ...OK into IN/KY... Multiple clusters of thunderstorms are ongoing this morning from the Ozarks into the lower Ohio Valley. Pockets of heating around these clusters will allow for the development of afternoon thunderstorms. Wind fields aloft are marginal for convective organization, but high surface dewpoint values and rather strong winds in the 1-3km layer suggest a few storms could occasionally produce gusty/damaging winds. ...Northeast states... Fast northwest flow aloft is present today across eastern Canada, and will spread into parts of NY and New England later today. Multiple progressive shortwave troughs embedded in the flow will help initiate scattered thunderstorms that track into the MRGL risk region this afternoon and evening. Relatively steep lapse rates and MLCAPE values of 1500+ J/kg may result in hail and/or gusty/damaging winds in a few of the stronger cells. Forecast coverage intense cells suggests that MRGL designation is appropriate today, but some potential exists for an upgrade later today if coverage exceeds expectations. ..Hart/Squitieri.. 08/15/2018 Read more

SPC Day 1 Fire Weather Outlook

4 hours 26 minutes ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1106 AM CDT Wed Aug 15 2018 Valid 151700Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHWEST OREGON... Added a small scattered DryT area along and east of the southern Oregon Cascades where storms are most likely. SREF and HREF guidance along with several CAMs all suggest storms are likely across this region. PWAT values are a bit on the wet side, but storm motions are forecast to be 25 to 35 mph which will help ignition efficiency. In addition, when dry, as they are now, fuels in this area are especially susceptible to fire starts, even when storms are wetter. ..Bentley.. 08/15/2018 .PREV DISCUSSION... /ISSUED 0140 AM CDT Wed Aug 15 2018/ ...Synopsis... As an upper-level trough amplifies across the western CONUS, a mid-level speed max will progress across Wyoming into the central/northern Plains today. Deep boundary-layer mixing is expected across portions of southwestern/south-central Wyoming during the afternoon. Enhanced mid-level flow will mix to the surface and promote 15-20 mph winds. With afternoon RH values falling to 5-15%, elevated fire weather conditions are expected. Across the Great Basin, northern Sierra Nevada, and into the Harney Basin of Oregon, mid-level moisture will be present and foster isolated afternoon thunderstorm development across the higher terrain. PWAT values will range from 0.5-0.8 in. across the region. Faster storm motions are expected in Oregon and northern Nevada with slower speeds in Utah. A mix of wet and dry storms appears likely, but with very dry fuels in place, lightning ignition efficiency will be high. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

4 hours 26 minutes ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1106 AM CDT Wed Aug 15 2018 Valid 151700Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHWEST OREGON... Added a small scattered DryT area along and east of the southern Oregon Cascades where storms are most likely. SREF and HREF guidance along with several CAMs all suggest storms are likely across this region. PWAT values are a bit on the wet side, but storm motions are forecast to be 25 to 35 mph which will help ignition efficiency. In addition, when dry, as they are now, fuels in this area are especially susceptible to fire starts, even when storms are wetter. ..Bentley.. 08/15/2018 .PREV DISCUSSION... /ISSUED 0140 AM CDT Wed Aug 15 2018/ ...Synopsis... As an upper-level trough amplifies across the western CONUS, a mid-level speed max will progress across Wyoming into the central/northern Plains today. Deep boundary-layer mixing is expected across portions of southwestern/south-central Wyoming during the afternoon. Enhanced mid-level flow will mix to the surface and promote 15-20 mph winds. With afternoon RH values falling to 5-15%, elevated fire weather conditions are expected. Across the Great Basin, northern Sierra Nevada, and into the Harney Basin of Oregon, mid-level moisture will be present and foster isolated afternoon thunderstorm development across the higher terrain. PWAT values will range from 0.5-0.8 in. across the region. Faster storm motions are expected in Oregon and northern Nevada with slower speeds in Utah. A mix of wet and dry storms appears likely, but with very dry fuels in place, lightning ignition efficiency will be high. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

4 hours 26 minutes ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1106 AM CDT Wed Aug 15 2018 Valid 151700Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHWEST OREGON... Added a small scattered DryT area along and east of the southern Oregon Cascades where storms are most likely. SREF and HREF guidance along with several CAMs all suggest storms are likely across this region. PWAT values are a bit on the wet side, but storm motions are forecast to be 25 to 35 mph which will help ignition efficiency. In addition, when dry, as they are now, fuels in this area are especially susceptible to fire starts, even when storms are wetter. ..Bentley.. 08/15/2018 .PREV DISCUSSION... /ISSUED 0140 AM CDT Wed Aug 15 2018/ ...Synopsis... As an upper-level trough amplifies across the western CONUS, a mid-level speed max will progress across Wyoming into the central/northern Plains today. Deep boundary-layer mixing is expected across portions of southwestern/south-central Wyoming during the afternoon. Enhanced mid-level flow will mix to the surface and promote 15-20 mph winds. With afternoon RH values falling to 5-15%, elevated fire weather conditions are expected. Across the Great Basin, northern Sierra Nevada, and into the Harney Basin of Oregon, mid-level moisture will be present and foster isolated afternoon thunderstorm development across the higher terrain. PWAT values will range from 0.5-0.8 in. across the region. Faster storm motions are expected in Oregon and northern Nevada with slower speeds in Utah. A mix of wet and dry storms appears likely, but with very dry fuels in place, lightning ignition efficiency will be high. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

4 hours 26 minutes ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1106 AM CDT Wed Aug 15 2018 Valid 151700Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHWEST OREGON... Added a small scattered DryT area along and east of the southern Oregon Cascades where storms are most likely. SREF and HREF guidance along with several CAMs all suggest storms are likely across this region. PWAT values are a bit on the wet side, but storm motions are forecast to be 25 to 35 mph which will help ignition efficiency. In addition, when dry, as they are now, fuels in this area are especially susceptible to fire starts, even when storms are wetter. ..Bentley.. 08/15/2018 .PREV DISCUSSION... /ISSUED 0140 AM CDT Wed Aug 15 2018/ ...Synopsis... As an upper-level trough amplifies across the western CONUS, a mid-level speed max will progress across Wyoming into the central/northern Plains today. Deep boundary-layer mixing is expected across portions of southwestern/south-central Wyoming during the afternoon. Enhanced mid-level flow will mix to the surface and promote 15-20 mph winds. With afternoon RH values falling to 5-15%, elevated fire weather conditions are expected. Across the Great Basin, northern Sierra Nevada, and into the Harney Basin of Oregon, mid-level moisture will be present and foster isolated afternoon thunderstorm development across the higher terrain. PWAT values will range from 0.5-0.8 in. across the region. Faster storm motions are expected in Oregon and northern Nevada with slower speeds in Utah. A mix of wet and dry storms appears likely, but with very dry fuels in place, lightning ignition efficiency will be high. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC MD 1293

6 hours 30 minutes ago
MD 1293 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR SOUTHWESTERN SOUTH DAKOTA...EXTREME NORTHWEST NEBRASKA
Mesoscale Discussion 1293 NWS Storm Prediction Center Norman OK 0903 AM CDT Wed Aug 15 2018 Areas affected...Southwestern South Dakota...extreme northwest Nebraska Concerning...Severe potential...Watch unlikely Valid 151403Z - 151630Z Probability of Watch Issuance...20 percent SUMMARY...Elevated thunderstorms capable of producing mainly severe hail are expected to persist along/north of the South Dakota/Nebraska border for at least a few more hours. A WW issuance is not currently anticipated. DISCUSSION...Elevated thunderstorms are currently ongoing across Fall River County, to Mellette County South Dakota. These storms have shown signs of organization/persistence, with up to 1.0-1.5 inch diameter MRMS-MESH occasionally noted with some of the stronger cells. An eastward propagating 500 mb shortwave trough and associated vort max, currently located across northeast Wyoming, has provided deep layer ascent to initiate this convection. Storms are currently rooted above a stable boundary layer, most likely above 850 mb (as indicated by 1300 UTC PFC RAP guidance). With up to around 500 J/kg MUCAPE, 30 knots of bulk effective shear, and continued deep-layer ascent associated with the vort max present across the discussion area, storms may persist for at least a few more hours, bearing a potential for at least marginally severe hail. Given the isolated and marginal extent of the severe hail threat, a WW issuance is not expected at this time. ..Squitieri/Hart.. 08/15/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ABR...LBF...UNR...CYS... LAT...LON 43050364 43350351 43450279 43560219 43720144 43850092 43770055 43679978 43409962 43109957 42839974 42840147 42780217 42930341 43050364 Read more

SPC Aug 15, 2018 1300 UTC Day 1 Convective Outlook

7 hours 30 minutes ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 15 2018 Valid 151300Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF NEBRASKA AND SOUTHERN SOUTH DAKOTA... ...SUMMARY... The main severe-storm threat area is over parts of the north-central Plains region this afternoon and evening, for large hail and severe gusts. ...Synopsis... The mid/upper-level pattern is transitioning toward a more-progressive regime over much of the CONUS, though the primary belt of midlatitude westerlies is forecast to remain to the north over Canada. A leading trough -- currently over New England and the coastal Mid-Atlantic, is forecast to eject across the Atlantic and Canadian Maritimes, while weakening. This will occur as an upstream perturbation -- now evident in moisture-channel imagery over northern ON -- shifts east-southeast and amplifies somewhat. The latter trough is forecast to reach northern New England between 06-12Z overnight, as a well-defined but lower-amplitude shortwave feature than the one now over New England. Farther west, a broad, weakening perturbation with several embedded vorticity lobes is apparent from IA across western MO to near the OK/AR border. The associated 500-mb trough should move to an axis from southern Lake Michigan to eastern AR by 00Z, then decelerate and deamplify across Lower MI, the IN/IL border area and western KY overnight. A pronounced, upstream trough -- currently located over eastern MT and eastern WY -- is expected to move eastward across the northern Plains through the period. Perhaps aided by convective vorticity generation/augmentation, this feature is progged to develop a closed 500-mb low this evening and overnight over southern SD, reaching the MHE-FSD vicinity by 12Z. At the surface, 11Z analysis showed a cold front from southern QC across southern Lake Huron to a frontal-wave low over the LSE area, then southwestward across western KS. The central U.s. portion of the cold front will merge with a prefrontal trough and weak low, associated with the weakening/departing mid/upper wave, through tonight. Meanwhile the eastern frontal segment will move southeastward across the St. Lawrence Valley, parts of Maine and northeastern NY by the end of the period. A dryline/mixing boundary should develop today over eastern CO/WY and move eastward this afternoon onto parts of the central High Plains as well. ...Northern/central Plains... Scattered thunderstorms are expected to form over the western parts of the outlook area through this afternoon -- including evolution of ongoing activity over the Black Hills vicinity into a destabilizing boundary layer farther east and southeast. Damaging gusts and large hail are expected from the most intense storms, some of which will be supercells capable of significant/2-inch or larger hail production, given the forecast lapse rates and shear. This process will be aided by steepened lapse rates from a combination of large-scale cooling/ascent in midlevels (ahead of the shortwave trough) with diabatic surface heating. Modified RAOBs and forecast soundings suggest surface dew points upper 50s to lower 60s F will support MLCAPE around 1500 J/kg, amidst sufficient veering of flow with height to contribute to 40-50-kt effective-shear magnitudes. Any relatively sustained/discrete cells may leave a swath of hail, in addition to isolated damaging gusts, while wind potential will be greater with any upscale clustering/cold-pool aggregation. Activity overall should diminish after about 04Z as the foregoing boundary layer diabatically stabilizes. ...Northeastern NM/southeastern CO southeastward... A relative gap in severe potential exists where drying and mixing will reduce CAPE substantially along and behind the boundary over northern/eastern CO, with only weak lift. However, widely scattered thunderstorms may develop over the Sangre de Cristos, and nearby foothills/mesas this afternoon and move southeast into a favorably well-mixed environment for isolated severe-gust potential. Storms should develop and intensify largely where the air mass can destabilize diabatically, with heating of higher terrain behind (north and northwest of the ongoing cloud/precip area in northeastern NM. ...Ohio Valley to eastern OK... Scattered thunderstorms will affect this corridor through the evening hours. Though most of the convection will be nonsevere, offering only localized potential for minor wind damage, isolated severe gusts may occur in the most intense, water-loaded cores. The already marginal severe potential will be very patchy/discontinuous through the outlook area, thanks to aftereffects of morning convection, related outflow and zones of differential heating that also may focus lift and low-level shear locally. Given the mesoscale uncertainties still involved, the outlook remains rather broadbrushed at this time. Rich low-level moisture largely is in place and will remain so, with surface dew points upper 60s to low 70s and PW commonly 1.75-2 inches. Any areas of sustained insolation will contribute to preconvective MLCAPE 1000-2000 J/kg over the lower Ohio Valley region, to over 3000 J/kg in eastern OK. Weak deep shear will limit overall severe potential, though pockets of enhanced low-level shear may develop around mesoscale boundaries and beneath a 30-40-kt southwesterly LLJ. ...Northern New England and northern NY... Widely scattered to scattered thunderstorms are expected to develop in multiple episodes today into this evening over the outlook area, and moving into the region from adjoining parts of Canada. Isolated marginally severe gusts are possible. Activity should occur along the front, as well as a prefrontal surface trough and perhaps boundaries left behind by morning clouds/precip. Surface dew points generally in the 60s F should combine with steep boundary-layer lapse rates to yield little or no CINH, with temps mid/upper 70s F and higher, based on forecast soundings. MLCAPE commonly should reach the 1500-2000 J/kg range (locally higher). Deep-layer flow should be nearly unidirectional/ westerly, which will limit convergence, through the aforementioned weak capping should permit storms to form along even subtle boundaries. Although low-level winds and shear will be weak, mid/ upper flow should strengthen with time this afternoon into evening, from west to east across the outlook area, as the shortwave trough approaches. This will aid in multicellular storm organization through increased cloud-layer shear. ..Edwards/Peters.. 08/15/2018 Read more

SPC Aug 15, 2018 1300 UTC Day 1 Convective Outlook

7 hours 30 minutes ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 15 2018 Valid 151300Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF NEBRASKA AND SOUTHERN SOUTH DAKOTA... ...SUMMARY... The main severe-storm threat area is over parts of the north-central Plains region this afternoon and evening, for large hail and severe gusts. ...Synopsis... The mid/upper-level pattern is transitioning toward a more-progressive regime over much of the CONUS, though the primary belt of midlatitude westerlies is forecast to remain to the north over Canada. A leading trough -- currently over New England and the coastal Mid-Atlantic, is forecast to eject across the Atlantic and Canadian Maritimes, while weakening. This will occur as an upstream perturbation -- now evident in moisture-channel imagery over northern ON -- shifts east-southeast and amplifies somewhat. The latter trough is forecast to reach northern New England between 06-12Z overnight, as a well-defined but lower-amplitude shortwave feature than the one now over New England. Farther west, a broad, weakening perturbation with several embedded vorticity lobes is apparent from IA across western MO to near the OK/AR border. The associated 500-mb trough should move to an axis from southern Lake Michigan to eastern AR by 00Z, then decelerate and deamplify across Lower MI, the IN/IL border area and western KY overnight. A pronounced, upstream trough -- currently located over eastern MT and eastern WY -- is expected to move eastward across the northern Plains through the period. Perhaps aided by convective vorticity generation/augmentation, this feature is progged to develop a closed 500-mb low this evening and overnight over southern SD, reaching the MHE-FSD vicinity by 12Z. At the surface, 11Z analysis showed a cold front from southern QC across southern Lake Huron to a frontal-wave low over the LSE area, then southwestward across western KS. The central U.s. portion of the cold front will merge with a prefrontal trough and weak low, associated with the weakening/departing mid/upper wave, through tonight. Meanwhile the eastern frontal segment will move southeastward across the St. Lawrence Valley, parts of Maine and northeastern NY by the end of the period. A dryline/mixing boundary should develop today over eastern CO/WY and move eastward this afternoon onto parts of the central High Plains as well. ...Northern/central Plains... Scattered thunderstorms are expected to form over the western parts of the outlook area through this afternoon -- including evolution of ongoing activity over the Black Hills vicinity into a destabilizing boundary layer farther east and southeast. Damaging gusts and large hail are expected from the most intense storms, some of which will be supercells capable of significant/2-inch or larger hail production, given the forecast lapse rates and shear. This process will be aided by steepened lapse rates from a combination of large-scale cooling/ascent in midlevels (ahead of the shortwave trough) with diabatic surface heating. Modified RAOBs and forecast soundings suggest surface dew points upper 50s to lower 60s F will support MLCAPE around 1500 J/kg, amidst sufficient veering of flow with height to contribute to 40-50-kt effective-shear magnitudes. Any relatively sustained/discrete cells may leave a swath of hail, in addition to isolated damaging gusts, while wind potential will be greater with any upscale clustering/cold-pool aggregation. Activity overall should diminish after about 04Z as the foregoing boundary layer diabatically stabilizes. ...Northeastern NM/southeastern CO southeastward... A relative gap in severe potential exists where drying and mixing will reduce CAPE substantially along and behind the boundary over northern/eastern CO, with only weak lift. However, widely scattered thunderstorms may develop over the Sangre de Cristos, and nearby foothills/mesas this afternoon and move southeast into a favorably well-mixed environment for isolated severe-gust potential. Storms should develop and intensify largely where the air mass can destabilize diabatically, with heating of higher terrain behind (north and northwest of the ongoing cloud/precip area in northeastern NM. ...Ohio Valley to eastern OK... Scattered thunderstorms will affect this corridor through the evening hours. Though most of the convection will be nonsevere, offering only localized potential for minor wind damage, isolated severe gusts may occur in the most intense, water-loaded cores. The already marginal severe potential will be very patchy/discontinuous through the outlook area, thanks to aftereffects of morning convection, related outflow and zones of differential heating that also may focus lift and low-level shear locally. Given the mesoscale uncertainties still involved, the outlook remains rather broadbrushed at this time. Rich low-level moisture largely is in place and will remain so, with surface dew points upper 60s to low 70s and PW commonly 1.75-2 inches. Any areas of sustained insolation will contribute to preconvective MLCAPE 1000-2000 J/kg over the lower Ohio Valley region, to over 3000 J/kg in eastern OK. Weak deep shear will limit overall severe potential, though pockets of enhanced low-level shear may develop around mesoscale boundaries and beneath a 30-40-kt southwesterly LLJ. ...Northern New England and northern NY... Widely scattered to scattered thunderstorms are expected to develop in multiple episodes today into this evening over the outlook area, and moving into the region from adjoining parts of Canada. Isolated marginally severe gusts are possible. Activity should occur along the front, as well as a prefrontal surface trough and perhaps boundaries left behind by morning clouds/precip. Surface dew points generally in the 60s F should combine with steep boundary-layer lapse rates to yield little or no CINH, with temps mid/upper 70s F and higher, based on forecast soundings. MLCAPE commonly should reach the 1500-2000 J/kg range (locally higher). Deep-layer flow should be nearly unidirectional/ westerly, which will limit convergence, through the aforementioned weak capping should permit storms to form along even subtle boundaries. Although low-level winds and shear will be weak, mid/ upper flow should strengthen with time this afternoon into evening, from west to east across the outlook area, as the shortwave trough approaches. This will aid in multicellular storm organization through increased cloud-layer shear. ..Edwards/Peters.. 08/15/2018 Read more
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