Aggregator

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Sep 11 2019 Valid 111630Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHEAST WYOMING...NORTHEAST COLORADO...AND WESTERN NEBRASKA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN WISCONSIN AND CENTRAL/SOUTHERN LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are expected over parts of the central High Plains, where large hail, damaging wind gusts and a few tornadoes are possible. Other severe storms may also affect portions of Wisconsin and Lower Michigan. ...High Plains... An upper trough over the western states will move slowly eastward today, with midlevel height falls and lift over the High Plains this afternoon and evening. Visible satellite imagery shows persistent low clouds over eastern WY/northeast CO/NE Panhandle, where easterly low-level winds and ample moisture are present. Current indications are that these clouds will burn off by mid-afternoon, allowing rapid destabilization and convective initiation. Other storms are likely to form along the eastern edge of the low clouds over northwest KS and southwest NE where strong heating will continue. All of this activity will be is environment of sufficient deep-layer shear for supercell structures. Large to very large hail will be the main threat through much of the afternoon and early evening, although an isolated tornado or two is possible with the more persistent supercells. As the low-level jet strengthen this evening, a more focused damaging wind threat may evolve over NE. ...WI/MI... A remnant MCV/shortwave trough is moving across western WI this morning. Strong heating ahead of the feature over southeast WI and southern Lower MI should aid in the re-development of scattered strong to severe storms my early afternoon. Forecast soundings show sufficient CAPE and mid level wind fields to promote damaging winds and some hail in the strongest cells. A few supercells are also possible - especially across central Lower MI in the vicinity of a weak surface boundary. Storms will track southeastward through the early evening before weakening. ...Western KS into TX Panhandle... Isolated strong thunderstorms will be possible once again today along the surface dryline over western KS and parts of the OK/TX Panhandles. Gusty winds and some hail will be possible for a few hours this afternoon and evening. ...OH/PA into Mid-Atlantic States... Strong heating and ample low level moisture will promote moderate CAPE values over parts of eastern OH, much of PA, and southward along an axis into parts of VA/NC. Scattered thunderstorms will affect this region, with a few of the storms posing a transient risk of gusty/damaging winds. ..Hart/Wendt.. 09/11/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Sep 11 2019 Valid 111630Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHEAST WYOMING...NORTHEAST COLORADO...AND WESTERN NEBRASKA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN WISCONSIN AND CENTRAL/SOUTHERN LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are expected over parts of the central High Plains, where large hail, damaging wind gusts and a few tornadoes are possible. Other severe storms may also affect portions of Wisconsin and Lower Michigan. ...High Plains... An upper trough over the western states will move slowly eastward today, with midlevel height falls and lift over the High Plains this afternoon and evening. Visible satellite imagery shows persistent low clouds over eastern WY/northeast CO/NE Panhandle, where easterly low-level winds and ample moisture are present. Current indications are that these clouds will burn off by mid-afternoon, allowing rapid destabilization and convective initiation. Other storms are likely to form along the eastern edge of the low clouds over northwest KS and southwest NE where strong heating will continue. All of this activity will be is environment of sufficient deep-layer shear for supercell structures. Large to very large hail will be the main threat through much of the afternoon and early evening, although an isolated tornado or two is possible with the more persistent supercells. As the low-level jet strengthen this evening, a more focused damaging wind threat may evolve over NE. ...WI/MI... A remnant MCV/shortwave trough is moving across western WI this morning. Strong heating ahead of the feature over southeast WI and southern Lower MI should aid in the re-development of scattered strong to severe storms my early afternoon. Forecast soundings show sufficient CAPE and mid level wind fields to promote damaging winds and some hail in the strongest cells. A few supercells are also possible - especially across central Lower MI in the vicinity of a weak surface boundary. Storms will track southeastward through the early evening before weakening. ...Western KS into TX Panhandle... Isolated strong thunderstorms will be possible once again today along the surface dryline over western KS and parts of the OK/TX Panhandles. Gusty winds and some hail will be possible for a few hours this afternoon and evening. ...OH/PA into Mid-Atlantic States... Strong heating and ample low level moisture will promote moderate CAPE values over parts of eastern OH, much of PA, and southward along an axis into parts of VA/NC. Scattered thunderstorms will affect this region, with a few of the storms posing a transient risk of gusty/damaging winds. ..Hart/Wendt.. 09/11/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Sep 11 2019 Valid 111630Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHEAST WYOMING...NORTHEAST COLORADO...AND WESTERN NEBRASKA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN WISCONSIN AND CENTRAL/SOUTHERN LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are expected over parts of the central High Plains, where large hail, damaging wind gusts and a few tornadoes are possible. Other severe storms may also affect portions of Wisconsin and Lower Michigan. ...High Plains... An upper trough over the western states will move slowly eastward today, with midlevel height falls and lift over the High Plains this afternoon and evening. Visible satellite imagery shows persistent low clouds over eastern WY/northeast CO/NE Panhandle, where easterly low-level winds and ample moisture are present. Current indications are that these clouds will burn off by mid-afternoon, allowing rapid destabilization and convective initiation. Other storms are likely to form along the eastern edge of the low clouds over northwest KS and southwest NE where strong heating will continue. All of this activity will be is environment of sufficient deep-layer shear for supercell structures. Large to very large hail will be the main threat through much of the afternoon and early evening, although an isolated tornado or two is possible with the more persistent supercells. As the low-level jet strengthen this evening, a more focused damaging wind threat may evolve over NE. ...WI/MI... A remnant MCV/shortwave trough is moving across western WI this morning. Strong heating ahead of the feature over southeast WI and southern Lower MI should aid in the re-development of scattered strong to severe storms my early afternoon. Forecast soundings show sufficient CAPE and mid level wind fields to promote damaging winds and some hail in the strongest cells. A few supercells are also possible - especially across central Lower MI in the vicinity of a weak surface boundary. Storms will track southeastward through the early evening before weakening. ...Western KS into TX Panhandle... Isolated strong thunderstorms will be possible once again today along the surface dryline over western KS and parts of the OK/TX Panhandles. Gusty winds and some hail will be possible for a few hours this afternoon and evening. ...OH/PA into Mid-Atlantic States... Strong heating and ample low level moisture will promote moderate CAPE values over parts of eastern OH, much of PA, and southward along an axis into parts of VA/NC. Scattered thunderstorms will affect this region, with a few of the storms posing a transient risk of gusty/damaging winds. ..Hart/Wendt.. 09/11/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Sep 11 2019 Valid 111630Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHEAST WYOMING...NORTHEAST COLORADO...AND WESTERN NEBRASKA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN WISCONSIN AND CENTRAL/SOUTHERN LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are expected over parts of the central High Plains, where large hail, damaging wind gusts and a few tornadoes are possible. Other severe storms may also affect portions of Wisconsin and Lower Michigan. ...High Plains... An upper trough over the western states will move slowly eastward today, with midlevel height falls and lift over the High Plains this afternoon and evening. Visible satellite imagery shows persistent low clouds over eastern WY/northeast CO/NE Panhandle, where easterly low-level winds and ample moisture are present. Current indications are that these clouds will burn off by mid-afternoon, allowing rapid destabilization and convective initiation. Other storms are likely to form along the eastern edge of the low clouds over northwest KS and southwest NE where strong heating will continue. All of this activity will be is environment of sufficient deep-layer shear for supercell structures. Large to very large hail will be the main threat through much of the afternoon and early evening, although an isolated tornado or two is possible with the more persistent supercells. As the low-level jet strengthen this evening, a more focused damaging wind threat may evolve over NE. ...WI/MI... A remnant MCV/shortwave trough is moving across western WI this morning. Strong heating ahead of the feature over southeast WI and southern Lower MI should aid in the re-development of scattered strong to severe storms my early afternoon. Forecast soundings show sufficient CAPE and mid level wind fields to promote damaging winds and some hail in the strongest cells. A few supercells are also possible - especially across central Lower MI in the vicinity of a weak surface boundary. Storms will track southeastward through the early evening before weakening. ...Western KS into TX Panhandle... Isolated strong thunderstorms will be possible once again today along the surface dryline over western KS and parts of the OK/TX Panhandles. Gusty winds and some hail will be possible for a few hours this afternoon and evening. ...OH/PA into Mid-Atlantic States... Strong heating and ample low level moisture will promote moderate CAPE values over parts of eastern OH, much of PA, and southward along an axis into parts of VA/NC. Scattered thunderstorms will affect this region, with a few of the storms posing a transient risk of gusty/damaging winds. ..Hart/Wendt.. 09/11/2019 Read more

No Mesoscale Discussions are in effect as of Wed Sep 11 16:27:01 UTC 2019.

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Wed Sep 11 2019 Valid 111700Z - 121200Z The ongoing forecast is on track and only minimal changes are made to the ongoing elevated area to reflect latest model trends. Later this afternoon, a southward-moving cold front is expected to traverse northern portions of the risk area and result in gusty, shifting winds. This may complicate any ongoing fire suppression efforts across the region. See the previous discussion below for more information. ..Cook.. 09/11/2019 .PREV DISCUSSION... /ISSUED 0107 AM CDT Wed Sep 11 2019/ ...Synopsis... A well-defined mid-level shortwave trough will move across the western CONUS, ejecting into the Plains states by the end of the period. Over 50 knots of 500 mb flow will accompany the trough, that when mixed down to the surface via a deepening boundary layer, will support dry and breezy conditions across the Four Corners areas. ...Four Corners Region... By mid to late afternoon, 15-25 mph sustained southwesterly surface winds, coincident with 15-25% RH, will become prevalent across northern portions of the Colorado Plateau, where an elevated area has been maintained. Very locally critical conditions will also be possible in terrain favoring locations, especially by peak afternoon heating. Given the sparse nature of the critical conditions, some modest precipitation accumulations within the last week, and fuels that are modestly receptive to fire spread, a critical delineation does not currently appear warranted. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Wed Sep 11 2019 Valid 111700Z - 121200Z The ongoing forecast is on track and only minimal changes are made to the ongoing elevated area to reflect latest model trends. Later this afternoon, a southward-moving cold front is expected to traverse northern portions of the risk area and result in gusty, shifting winds. This may complicate any ongoing fire suppression efforts across the region. See the previous discussion below for more information. ..Cook.. 09/11/2019 .PREV DISCUSSION... /ISSUED 0107 AM CDT Wed Sep 11 2019/ ...Synopsis... A well-defined mid-level shortwave trough will move across the western CONUS, ejecting into the Plains states by the end of the period. Over 50 knots of 500 mb flow will accompany the trough, that when mixed down to the surface via a deepening boundary layer, will support dry and breezy conditions across the Four Corners areas. ...Four Corners Region... By mid to late afternoon, 15-25 mph sustained southwesterly surface winds, coincident with 15-25% RH, will become prevalent across northern portions of the Colorado Plateau, where an elevated area has been maintained. Very locally critical conditions will also be possible in terrain favoring locations, especially by peak afternoon heating. Given the sparse nature of the critical conditions, some modest precipitation accumulations within the last week, and fuels that are modestly receptive to fire spread, a critical delineation does not currently appear warranted. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Wed Sep 11 2019 Valid 111700Z - 121200Z The ongoing forecast is on track and only minimal changes are made to the ongoing elevated area to reflect latest model trends. Later this afternoon, a southward-moving cold front is expected to traverse northern portions of the risk area and result in gusty, shifting winds. This may complicate any ongoing fire suppression efforts across the region. See the previous discussion below for more information. ..Cook.. 09/11/2019 .PREV DISCUSSION... /ISSUED 0107 AM CDT Wed Sep 11 2019/ ...Synopsis... A well-defined mid-level shortwave trough will move across the western CONUS, ejecting into the Plains states by the end of the period. Over 50 knots of 500 mb flow will accompany the trough, that when mixed down to the surface via a deepening boundary layer, will support dry and breezy conditions across the Four Corners areas. ...Four Corners Region... By mid to late afternoon, 15-25 mph sustained southwesterly surface winds, coincident with 15-25% RH, will become prevalent across northern portions of the Colorado Plateau, where an elevated area has been maintained. Very locally critical conditions will also be possible in terrain favoring locations, especially by peak afternoon heating. Given the sparse nature of the critical conditions, some modest precipitation accumulations within the last week, and fuels that are modestly receptive to fire spread, a critical delineation does not currently appear warranted. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Wed Sep 11 2019 Valid 111700Z - 121200Z The ongoing forecast is on track and only minimal changes are made to the ongoing elevated area to reflect latest model trends. Later this afternoon, a southward-moving cold front is expected to traverse northern portions of the risk area and result in gusty, shifting winds. This may complicate any ongoing fire suppression efforts across the region. See the previous discussion below for more information. ..Cook.. 09/11/2019 .PREV DISCUSSION... /ISSUED 0107 AM CDT Wed Sep 11 2019/ ...Synopsis... A well-defined mid-level shortwave trough will move across the western CONUS, ejecting into the Plains states by the end of the period. Over 50 knots of 500 mb flow will accompany the trough, that when mixed down to the surface via a deepening boundary layer, will support dry and breezy conditions across the Four Corners areas. ...Four Corners Region... By mid to late afternoon, 15-25 mph sustained southwesterly surface winds, coincident with 15-25% RH, will become prevalent across northern portions of the Colorado Plateau, where an elevated area has been maintained. Very locally critical conditions will also be possible in terrain favoring locations, especially by peak afternoon heating. Given the sparse nature of the critical conditions, some modest precipitation accumulations within the last week, and fuels that are modestly receptive to fire spread, a critical delineation does not currently appear warranted. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Wed Sep 11 2019 Valid 111300Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING OVER PARTS OF THE CENTRAL HIGH PLAINS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING FROM PORTIONS OF WISCONSIN ACROSS PARTS OF LOWER MICHIGAN... ...SUMMARY... The greatest severe-storm risk is today into this evening over parts of the central High Plains, where large, damaging hail and severe gusts are expected, and a few tornadoes are possible. ...Synopsis... A progressive westerly wave train will characterize the general upper-air pattern over the northern 1/2-2/3 of the CONUS this period. the main feature aloft aiding severe potential will be a synoptic-scale trough -- initially evident in moisture-channel imagery over western MT, ID, eastern NV, and the lower Colorado River Valley. This trough will move to an axis near GTF-JAC-PGA by 00Z, and GGW-CDR-ALS by 12Z, with an intermittently closed 500-mb low shifting eastward across MT. To its east, an MCV is noted in midlevel satellite imagery and composited radar loops over eastern MN, with shortwave trough southward over southern MN. This perturbation should proceed eastward across WI, Lake Michigan, and part of northern Lower Michigan through this evening. At the surface, the 11Z analyses showed a wavy, mostly stationary front from Lake Ontario across southern Lower MI and southern WI, to a low near LSE, then west-southwestward across southeastern SD and northwestern NE, behind some convective outflow. The outflow boundary extended across northeastern/central IA and south-central NE near I-80. An elongated low-pressure area was located from southeastern WY across eastern CO. The low-pressure area should consolidate through the day, then shift roughly northeastward across NE overnight, reaching the FSD vicinity by 12Z. A cold front will sweep southward/southeastward across the central Great Plains behind that low, reaching east-central NE, north-central/southwestern KS and the Raton Mesa area by 12Z. The eastern frontal segment should settle somewhat southward across the mid-Atlantic region, but remain quasistationary from there to near the Mississippi River, modulated on the mesoscale by MCS outflow over the southern Upper Great Lakes region. The combined front/outflow boundary also should move slowly northward as a warm front ahead of that low tonight over eastern NE/IA. ...Central Plains... Scattered thunderstorms, including a few supercells, are forecast to form over higher terrain of eastern WY as early as midday to early afternoon, in the presence of strengthening deep-layer forcing that precedes the mid/upper trough. This activity should move generally eastward across the NE Panhandle/Sandhills regions, and perhaps adjoining parts of southern SD, offering the threat for all forms of severe. The most supportive parameter space may develop over portions of west-central NE, where rich low-level moisture should advect into the region. This will be most pronounced along and south of the northward-moving outflow boundary merging with the synoptic front -- in the eastern sector of the low-level cyclogenesis and associated mass response to the approaching synoptic trough. Favorable mid/ upper-level lapse rates and a deeply buoyant troposphere overlying that moisture, in combination with diabatic surface heating, will contribute to MLCAPE in the 2000-3500 J/kg range. Veering low-level winds with height will contribute to favorable deep shear (e.g., 40- 50-kt effective-shear magnitudes), though lack of stronger speeds in low levels may temper hodograph size somewhat away from mesobeta- to local-scale boundary influences. Still, with the boundary and supercell-favorable bulk shear, a tornado risk does exist, along with the potential for very large/damaging hail of 2 inches or larger in diameter. Another upscale-growth process is forecast to evolve from the early supercell and multicell activity, amidst general height falls and increasing large-scale forcing for ascent that precedes the progressive mid/upper trough. This should result in an evening/ overnight MCS sweeping into a recovering air mass located from central/northeastern NE into the Siouxland area. Damaging and severe gusts will be the main concern once the MCS develops, though brief/embedded QLCS mesovortices may develop for an isolated threat of tornadoes. ...Upper Great Lakes region... Isolated strong-severe gusts cannot be ruled out the next few hours from the MCS crossing the upper Mississippi Valley, particularly in the warm sector and very near the front on the north side, with increasing static stability in the boundary layer reducing that potential northward across western WI and Lake Michigan. MCS outflow has stabilized much of the boundary layer in the original outlook area(s) across IA, rendering unconditional severe potential marginal in nature and skewed toward late in the period, as the outflow/frontal zone moves back northward. A continuation of the MCS and/or additional convective development near the front/outflow boundary will pose a greater threat of severe from midday through at least early evening, shifting eastward to east-southeastward across the eastern "slight risk" area. Damaging gusts will be the main concern, though supercell-favorable kinematic fields will exist near the boundary, compelling marginal tornado/ hail lines for part of the region. The low-level air mass in the baroclinic zone and south of the surface boundary will destabilize today from a combination of thetae advection and pockets of sustained diabatic surface heating. This will boost boundary-layer lapse rates and overall buoyancy amidst favorable moisture. Surface dew points in the upper 60s to lower 70s F and PW around 1.75 inch should be common along and south of the preconvective frontal zone today, contributing to 1500-2500 J/kg MLCAPE. 30-40-kt effective- shear magnitudes and somewhat enlarged low-level hodographs (with 200-300 J/kg effective SRH near the boundary) are possible, despite the area's being under the upper ridge. ..Edwards/Dial.. 09/11/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Wed Sep 11 2019 Valid 111300Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING OVER PARTS OF THE CENTRAL HIGH PLAINS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING FROM PORTIONS OF WISCONSIN ACROSS PARTS OF LOWER MICHIGAN... ...SUMMARY... The greatest severe-storm risk is today into this evening over parts of the central High Plains, where large, damaging hail and severe gusts are expected, and a few tornadoes are possible. ...Synopsis... A progressive westerly wave train will characterize the general upper-air pattern over the northern 1/2-2/3 of the CONUS this period. the main feature aloft aiding severe potential will be a synoptic-scale trough -- initially evident in moisture-channel imagery over western MT, ID, eastern NV, and the lower Colorado River Valley. This trough will move to an axis near GTF-JAC-PGA by 00Z, and GGW-CDR-ALS by 12Z, with an intermittently closed 500-mb low shifting eastward across MT. To its east, an MCV is noted in midlevel satellite imagery and composited radar loops over eastern MN, with shortwave trough southward over southern MN. This perturbation should proceed eastward across WI, Lake Michigan, and part of northern Lower Michigan through this evening. At the surface, the 11Z analyses showed a wavy, mostly stationary front from Lake Ontario across southern Lower MI and southern WI, to a low near LSE, then west-southwestward across southeastern SD and northwestern NE, behind some convective outflow. The outflow boundary extended across northeastern/central IA and south-central NE near I-80. An elongated low-pressure area was located from southeastern WY across eastern CO. The low-pressure area should consolidate through the day, then shift roughly northeastward across NE overnight, reaching the FSD vicinity by 12Z. A cold front will sweep southward/southeastward across the central Great Plains behind that low, reaching east-central NE, north-central/southwestern KS and the Raton Mesa area by 12Z. The eastern frontal segment should settle somewhat southward across the mid-Atlantic region, but remain quasistationary from there to near the Mississippi River, modulated on the mesoscale by MCS outflow over the southern Upper Great Lakes region. The combined front/outflow boundary also should move slowly northward as a warm front ahead of that low tonight over eastern NE/IA. ...Central Plains... Scattered thunderstorms, including a few supercells, are forecast to form over higher terrain of eastern WY as early as midday to early afternoon, in the presence of strengthening deep-layer forcing that precedes the mid/upper trough. This activity should move generally eastward across the NE Panhandle/Sandhills regions, and perhaps adjoining parts of southern SD, offering the threat for all forms of severe. The most supportive parameter space may develop over portions of west-central NE, where rich low-level moisture should advect into the region. This will be most pronounced along and south of the northward-moving outflow boundary merging with the synoptic front -- in the eastern sector of the low-level cyclogenesis and associated mass response to the approaching synoptic trough. Favorable mid/ upper-level lapse rates and a deeply buoyant troposphere overlying that moisture, in combination with diabatic surface heating, will contribute to MLCAPE in the 2000-3500 J/kg range. Veering low-level winds with height will contribute to favorable deep shear (e.g., 40- 50-kt effective-shear magnitudes), though lack of stronger speeds in low levels may temper hodograph size somewhat away from mesobeta- to local-scale boundary influences. Still, with the boundary and supercell-favorable bulk shear, a tornado risk does exist, along with the potential for very large/damaging hail of 2 inches or larger in diameter. Another upscale-growth process is forecast to evolve from the early supercell and multicell activity, amidst general height falls and increasing large-scale forcing for ascent that precedes the progressive mid/upper trough. This should result in an evening/ overnight MCS sweeping into a recovering air mass located from central/northeastern NE into the Siouxland area. Damaging and severe gusts will be the main concern once the MCS develops, though brief/embedded QLCS mesovortices may develop for an isolated threat of tornadoes. ...Upper Great Lakes region... Isolated strong-severe gusts cannot be ruled out the next few hours from the MCS crossing the upper Mississippi Valley, particularly in the warm sector and very near the front on the north side, with increasing static stability in the boundary layer reducing that potential northward across western WI and Lake Michigan. MCS outflow has stabilized much of the boundary layer in the original outlook area(s) across IA, rendering unconditional severe potential marginal in nature and skewed toward late in the period, as the outflow/frontal zone moves back northward. A continuation of the MCS and/or additional convective development near the front/outflow boundary will pose a greater threat of severe from midday through at least early evening, shifting eastward to east-southeastward across the eastern "slight risk" area. Damaging gusts will be the main concern, though supercell-favorable kinematic fields will exist near the boundary, compelling marginal tornado/ hail lines for part of the region. The low-level air mass in the baroclinic zone and south of the surface boundary will destabilize today from a combination of thetae advection and pockets of sustained diabatic surface heating. This will boost boundary-layer lapse rates and overall buoyancy amidst favorable moisture. Surface dew points in the upper 60s to lower 70s F and PW around 1.75 inch should be common along and south of the preconvective frontal zone today, contributing to 1500-2500 J/kg MLCAPE. 30-40-kt effective- shear magnitudes and somewhat enlarged low-level hodographs (with 200-300 J/kg effective SRH near the boundary) are possible, despite the area's being under the upper ridge. ..Edwards/Dial.. 09/11/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Wed Sep 11 2019 Valid 111300Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING OVER PARTS OF THE CENTRAL HIGH PLAINS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY INTO THIS EVENING FROM PORTIONS OF WISCONSIN ACROSS PARTS OF LOWER MICHIGAN... ...SUMMARY... The greatest severe-storm risk is today into this evening over parts of the central High Plains, where large, damaging hail and severe gusts are expected, and a few tornadoes are possible. ...Synopsis... A progressive westerly wave train will characterize the general upper-air pattern over the northern 1/2-2/3 of the CONUS this period. the main feature aloft aiding severe potential will be a synoptic-scale trough -- initially evident in moisture-channel imagery over western MT, ID, eastern NV, and the lower Colorado River Valley. This trough will move to an axis near GTF-JAC-PGA by 00Z, and GGW-CDR-ALS by 12Z, with an intermittently closed 500-mb low shifting eastward across MT. To its east, an MCV is noted in midlevel satellite imagery and composited radar loops over eastern MN, with shortwave trough southward over southern MN. This perturbation should proceed eastward across WI, Lake Michigan, and part of northern Lower Michigan through this evening. At the surface, the 11Z analyses showed a wavy, mostly stationary front from Lake Ontario across southern Lower MI and southern WI, to a low near LSE, then west-southwestward across southeastern SD and northwestern NE, behind some convective outflow. The outflow boundary extended across northeastern/central IA and south-central NE near I-80. An elongated low-pressure area was located from southeastern WY across eastern CO. The low-pressure area should consolidate through the day, then shift roughly northeastward across NE overnight, reaching the FSD vicinity by 12Z. A cold front will sweep southward/southeastward across the central Great Plains behind that low, reaching east-central NE, north-central/southwestern KS and the Raton Mesa area by 12Z. The eastern frontal segment should settle somewhat southward across the mid-Atlantic region, but remain quasistationary from there to near the Mississippi River, modulated on the mesoscale by MCS outflow over the southern Upper Great Lakes region. The combined front/outflow boundary also should move slowly northward as a warm front ahead of that low tonight over eastern NE/IA. ...Central Plains... Scattered thunderstorms, including a few supercells, are forecast to form over higher terrain of eastern WY as early as midday to early afternoon, in the presence of strengthening deep-layer forcing that precedes the mid/upper trough. This activity should move generally eastward across the NE Panhandle/Sandhills regions, and perhaps adjoining parts of southern SD, offering the threat for all forms of severe. The most supportive parameter space may develop over portions of west-central NE, where rich low-level moisture should advect into the region. This will be most pronounced along and south of the northward-moving outflow boundary merging with the synoptic front -- in the eastern sector of the low-level cyclogenesis and associated mass response to the approaching synoptic trough. Favorable mid/ upper-level lapse rates and a deeply buoyant troposphere overlying that moisture, in combination with diabatic surface heating, will contribute to MLCAPE in the 2000-3500 J/kg range. Veering low-level winds with height will contribute to favorable deep shear (e.g., 40- 50-kt effective-shear magnitudes), though lack of stronger speeds in low levels may temper hodograph size somewhat away from mesobeta- to local-scale boundary influences. Still, with the boundary and supercell-favorable bulk shear, a tornado risk does exist, along with the potential for very large/damaging hail of 2 inches or larger in diameter. Another upscale-growth process is forecast to evolve from the early supercell and multicell activity, amidst general height falls and increasing large-scale forcing for ascent that precedes the progressive mid/upper trough. This should result in an evening/ overnight MCS sweeping into a recovering air mass located from central/northeastern NE into the Siouxland area. Damaging and severe gusts will be the main concern once the MCS develops, though brief/embedded QLCS mesovortices may develop for an isolated threat of tornadoes. ...Upper Great Lakes region... Isolated strong-severe gusts cannot be ruled out the next few hours from the MCS crossing the upper Mississippi Valley, particularly in the warm sector and very near the front on the north side, with increasing static stability in the boundary layer reducing that potential northward across western WI and Lake Michigan. MCS outflow has stabilized much of the boundary layer in the original outlook area(s) across IA, rendering unconditional severe potential marginal in nature and skewed toward late in the period, as the outflow/frontal zone moves back northward. A continuation of the MCS and/or additional convective development near the front/outflow boundary will pose a greater threat of severe from midday through at least early evening, shifting eastward to east-southeastward across the eastern "slight risk" area. Damaging gusts will be the main concern, though supercell-favorable kinematic fields will exist near the boundary, compelling marginal tornado/ hail lines for part of the region. The low-level air mass in the baroclinic zone and south of the surface boundary will destabilize today from a combination of thetae advection and pockets of sustained diabatic surface heating. This will boost boundary-layer lapse rates and overall buoyancy amidst favorable moisture. Surface dew points in the upper 60s to lower 70s F and PW around 1.75 inch should be common along and south of the preconvective frontal zone today, contributing to 1500-2500 J/kg MLCAPE. 30-40-kt effective- shear magnitudes and somewhat enlarged low-level hodographs (with 200-300 J/kg effective SRH near the boundary) are possible, despite the area's being under the upper ridge. ..Edwards/Dial.. 09/11/2019 Read more

000
ABPZ20 KNHC 111130
TWOEP

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Wed Sep 11 2019

For the eastern North Pacific...east of 140 degrees west longitude:

A broad area of low pressure located several hundred miles
west-southwest of Acapulco, Mexico, is gradually becoming better
defined. Environmental conditions are conducive for further
development of this disturbance, and a tropical depression is likely
to form within the next couple of days while the low moves westward
to west-northwestward at 10 to 15 mph.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...90 percent.

An area of low pressure is expected to form more than 1000 miles to
the southwest of the southern tip of the Baja California Peninsula
during the next couple of days. Some additional development is
possible while the system moves slowly westward through the
weekend and early next week.
* Formation chance through 48 hours...low...near 10 percent.
* Formation chance through 5 days...low...30 percent.

$$
Forecaster Latto

WW 0644 Status Updates
STATUS REPORT ON WW 644 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 30 NNE FOD TO 25 E MKT. ..DIAL..09/11/19 ATTN...WFO...DMX...ARX...MPX... STATUS REPORT FOR WS 644 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC033-067-081-131-189-195-111040- IA . IOWA COUNTIES INCLUDED ARE CERRO GORDO FLOYD HANCOCK MITCHELL WINNEBAGO WORTH MNC039-047-099-147-111040- MN . MINNESOTA COUNTIES INCLUDED ARE DODGE FREEBORN MOWER STEELE THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 644 SEVERE TSTM IA MN 110545Z - 111100Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 644 NWS Storm Prediction Center Norman OK 1245 AM CDT Wed Sep 11 2019 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northern Iowa Southern Minnesota * Effective this Wednesday morning from 1245 AM until 600 AM CDT. * Primary threats include... Scattered damaging winds and isolated significant gusts to 75 mph possible Isolated large hail events to 1 inch in diameter possible A tornado or two possible SUMMARY...A complex of thunderstorms, having produced measured severe winds and a brief tornado in the Sioux Falls area, is expected to maintain some severe threat for a few more hours as it moves astride a sharply defined front located very near the Minnesota/Iowa border. Damaging gusts will be the main concern, though a tornado cannot be ruled out, and isolated hail also is possible with cells ahead of the main complex. The severe thunderstorm watch area is approximately along and 40 statute miles north and south of a line from 25 miles west southwest of Fairmont MN to 45 miles northeast of Mason City IA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU4). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 643... AVIATION...A few severe thunderstorms with hail surface and aloft to 1 inch. Extreme turbulence and surface wind gusts to 65 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 26035. ...Edwards Read more

WW 0644 Status Updates
STATUS REPORT ON WW 644 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 20 NE SPW TO 15 NNE FRM TO 10 WSW MKT. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1954 ..DIAL..09/11/19 ATTN...WFO...DMX...ARX...MPX... STATUS REPORT FOR WS 644 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC033-063-067-081-109-131-147-189-195-110940- IA . IOWA COUNTIES INCLUDED ARE CERRO GORDO EMMET FLOYD HANCOCK KOSSUTH MITCHELL PALO ALTO WINNEBAGO WORTH MNC013-039-043-047-099-147-161-110940- MN . MINNESOTA COUNTIES INCLUDED ARE BLUE EARTH DODGE FARIBAULT FREEBORN MOWER STEELE WASECA THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES Read more

WW 0643 Status Updates
STATUS REPORT ON WW 643 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 WNW SLB TO 10 E SPW. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1954 ..DIAL..09/11/19 ATTN...WFO...FSD...LBF...OAX... STATUS REPORT FOR WS 643 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC021-093-193-110940- IA . IOWA COUNTIES INCLUDED ARE BUENA VISTA IDA WOODBURY THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 0643 Status Updates
STATUS REPORT ON WW 643 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 WNW SLB TO 10 E SPW. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1954 ..DIAL..09/11/19 ATTN...WFO...FSD...LBF...OAX... STATUS REPORT FOR WS 643 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC021-093-193-110940- IA . IOWA COUNTIES INCLUDED ARE BUENA VISTA IDA WOODBURY THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 643 SEVERE TSTM IA MN NE SD 110135Z - 110900Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 643 NWS Storm Prediction Center Norman OK 835 PM CDT Tue Sep 10 2019 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northwest Iowa Southwest Minnesota Northeast Nebraska Southeast South Dakota * Effective this Tuesday night and Wednesday morning from 835 PM until 400 AM CDT. * Primary threats include... Scattered damaging winds and isolated significant gusts to 75 mph likely Scattered large hail and isolated very large hail events to 2 inches in diameter possible A tornado or two possible SUMMARY...Clusters of storms will continue to merge and grow upscale into a larger convective system that will spread eastward overnight with an attendant threat for damaging winds and large hail. In the short term, a supercell moving into Bon Homme County South Dakota will pose a threat for a tornado or two before being overtaken and merging with the clusters to the west. The severe thunderstorm watch area is approximately along and 45 statute miles north and south of a line from 35 miles northwest of Oneill NE to 20 miles north northeast of Spencer IA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU3). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...This severe thunderstorm watch replaces severe thunderstorm watch number 642. Watch number 642 will not be in effect after 835 PM CDT. CONTINUE...WW 640...WW 641... AVIATION...A few severe thunderstorms with hail surface and aloft to 2 inches. Extreme turbulence and surface wind gusts to 65 knots. A few cumulonimbi with maximum tops to 550. Mean storm motion vector 27025. ...Thompson Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0242 AM CDT Wed Sep 11 2019 Valid 141200Z - 191200Z ...DISCUSSION... ...Saturday/Day 4 and Sunday/Day 5... On Saturday, the medium-range models show a west-to east mid-level flow pattern across the northern U.S. and move a shortwave trough across the northern Plains. A cold front associated with the trough is forecast to move eastward into the upper Mississippi Valley and mid Missouri Valley. Although the models keep the warm sector capped through much of the day, some convection will be possible along the front during the evening and overnight period. An isolated severe threat will be possible, but will depend upon how much instability develops ahead of the front. On Sunday, the models move the shortwave trough eastward across the Great Lakes and develop an upper-level ridge in the north-central U.S. Thunderstorms would be possible Sunday afternoon in parts of the lower Great Lakes region along and south of a cold front. ...Monday/Day 6 to Wednesday/day 8... An upper-level ridge is forecast to develop across the eastern half of the U.S. from Monday to Wednesday as an upper-level trough takes shape in the western states. Model spread is considerable concerning where the greatest instability will develop each day beneath the ridge. Although an isolated severe threat can not be ruled out from the northern Plains eastward into the Upper Mississippi Valley each day, uncertainty is substantial during this part of the forecast period. Read more