Severe Storms

WW 630 SEVERE TSTM AZ 012235Z - 020600Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 630 NWS Storm Prediction Center Norman OK 335 PM MST Sun Sep 1 2019 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Central and western Arizona * Effective this Sunday afternoon and evening from 335 PM until 1100 PM MST. * Primary threats include... Scattered damaging winds and isolated significant gusts to 75 mph possible SUMMARY...Although isolated strong-severe storms already are occurring, the potential is increasing for one or two organized clusters to grow and send damaging to severe gusts westward across the deserts. The main threat area will be from that part of Pima County west of Tucson, northward across central Arizona, and the southern part of the I-17 corridor, westward to near the Colorado River. The severe thunderstorm watch area is approximately along and 105 statute miles east and west of a line from Prescott AZ to 75 miles south of Gila Bend AZ. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU0). 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. && 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 550. Mean storm motion vector 09035. ...Edwards Read more

WW 0630 Status Updates
STATUS REPORT ON WW 630 THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA. ..BROYLES..09/02/19 ATTN...WFO...PSR...TWC...FGZ... STATUS REPORT FOR WS 630 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS AZC012-013-019-021-025-027-020240- AZ . ARIZONA COUNTIES INCLUDED ARE LA PAZ MARICOPA PIMA PINAL YAVAPAI YUMA 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

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Sun Sep 01 2019 Valid 020100Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are likely across parts of central and southern Arizona this evening. A few strong to severe storms remain possible over western Pennsylvania through mid evening and over the central and northern Plains later tonight. ...Central and southern Arizona... Easterly deep-layer winds along southern periphery of an upper ridge have promoted storms that developed over the mountains of southeast AZ moving westward into the desert valleys. Tendency has been for storms to evolve into multicell clusters. Deep, inverted-V well-mixed boundary layers as indicated by the 00Z RAOB data will continue to promote scattered damaging wind gusts as storms continue westward this evening. ...Western Pennsylvania... A cluster of storms continues through western PA in association with a low-amplitude shortwave trough. The 00Z Pittsburgh RAOB indicates around 1500 J/kg MLCAPE and 160 m2/s2 0-1 km storm-relative helicity, but modest effective bulk shear. This environment may continue to support a marginal risk for locally strong wind gusts and perhaps a brief tornado with transient supercell structures before weakening toward mid evening. ...Central through northern Plains... Isolated storms remain possible later tonight within zone of increasing warm advection and isentropic ascent as the low-level jet strengthens and interacts with baroclinic zone across the central and northern Plains. These storms will be elevated, but moderate MUCAPE and 35-40 kt effective bulk shear will support mid-level updraft rotation along with a risk for a few instances of hail and locally strong wind gusts. ..Dial.. 09/02/2019 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Sun Sep 01 2019 Valid 020100Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are likely across parts of central and southern Arizona this evening. A few strong to severe storms remain possible over western Pennsylvania through mid evening and over the central and northern Plains later tonight. ...Central and southern Arizona... Easterly deep-layer winds along southern periphery of an upper ridge have promoted storms that developed over the mountains of southeast AZ moving westward into the desert valleys. Tendency has been for storms to evolve into multicell clusters. Deep, inverted-V well-mixed boundary layers as indicated by the 00Z RAOB data will continue to promote scattered damaging wind gusts as storms continue westward this evening. ...Western Pennsylvania... A cluster of storms continues through western PA in association with a low-amplitude shortwave trough. The 00Z Pittsburgh RAOB indicates around 1500 J/kg MLCAPE and 160 m2/s2 0-1 km storm-relative helicity, but modest effective bulk shear. This environment may continue to support a marginal risk for locally strong wind gusts and perhaps a brief tornado with transient supercell structures before weakening toward mid evening. ...Central through northern Plains... Isolated storms remain possible later tonight within zone of increasing warm advection and isentropic ascent as the low-level jet strengthens and interacts with baroclinic zone across the central and northern Plains. These storms will be elevated, but moderate MUCAPE and 35-40 kt effective bulk shear will support mid-level updraft rotation along with a risk for a few instances of hail and locally strong wind gusts. ..Dial.. 09/02/2019 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Sun Sep 01 2019 Valid 020100Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are likely across parts of central and southern Arizona this evening. A few strong to severe storms remain possible over western Pennsylvania through mid evening and over the central and northern Plains later tonight. ...Central and southern Arizona... Easterly deep-layer winds along southern periphery of an upper ridge have promoted storms that developed over the mountains of southeast AZ moving westward into the desert valleys. Tendency has been for storms to evolve into multicell clusters. Deep, inverted-V well-mixed boundary layers as indicated by the 00Z RAOB data will continue to promote scattered damaging wind gusts as storms continue westward this evening. ...Western Pennsylvania... A cluster of storms continues through western PA in association with a low-amplitude shortwave trough. The 00Z Pittsburgh RAOB indicates around 1500 J/kg MLCAPE and 160 m2/s2 0-1 km storm-relative helicity, but modest effective bulk shear. This environment may continue to support a marginal risk for locally strong wind gusts and perhaps a brief tornado with transient supercell structures before weakening toward mid evening. ...Central through northern Plains... Isolated storms remain possible later tonight within zone of increasing warm advection and isentropic ascent as the low-level jet strengthens and interacts with baroclinic zone across the central and northern Plains. These storms will be elevated, but moderate MUCAPE and 35-40 kt effective bulk shear will support mid-level updraft rotation along with a risk for a few instances of hail and locally strong wind gusts. ..Dial.. 09/02/2019 Read more

MD 1909 CONCERNING SEVERE THUNDERSTORM WATCH 630... FOR SOUTHEAST CALIFORNIA...SOUTHWEST AND CENTRAL ARIZONA
Mesoscale Discussion 1909 NWS Storm Prediction Center Norman OK 0725 PM CDT Sun Sep 01 2019 Areas affected...Southeast California...Southwest and Central Arizona Concerning...Severe Thunderstorm Watch 630... Valid 020025Z - 020230Z The severe weather threat for Severe Thunderstorm Watch 630 continues. SUMMARY...A wind-damage threat will continue across central and western parts of WW 630 over the next several hours. DISCUSSION...The latest radar imagery across southern and central Arizona shows a couple of areas of strong thunderstorms. The first is located between the Flagstaff and Phoenix area with the second to the southwest of the Phoenix near the Arizona-Mexico border. The RAP is analyzing moderate instability across the southern half of Arizona with the strongest instability located in southwestern Arizona where MLCAPE values are estimated near 2500 J/kg. The wind profile is from the east with 20 to 25 kt of flow near 500 mb as evidenced on the Tuscon 00Z sounding. This combined with hot surface temperatures and a nearly dry adiabatic layer from the surface to 700 mb should promote isolated damaging wind gusts with the stronger multicells. ..Broyles.. 09/02/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TWC...FGZ...PSR...VEF... LAT...LON 31861308 33071162 33941144 34731188 35041288 35161379 34701447 33951490 32491502 31861308 Read more

MD 1908 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PARTS OF EASTERN OHIO...WESTERN PENNSYLVANIA...FAR SOUTHWEST NEW YORK
Mesoscale Discussion 1908 NWS Storm Prediction Center Norman OK 0626 PM CDT Sun Sep 01 2019 Areas affected...Parts of eastern Ohio...western Pennsylvania...far southwest New York Concerning...Severe potential...Watch unlikely Valid 012326Z - 020100Z Probability of Watch Issuance...5 percent SUMMARY...A brief increase in convective coverage and perhaps intensity may occur over the next few hours. The stronger storms may produce isolated damaging wind gusts, marginally severe hail, and possibly a brief tornado. The isolated nature of the risk precludes a WW issuance. DISCUSSION...Scattered storms have been developing for much of the afternoon along a axis of a passing mid-level shortwave trough. Recently, mosaic radar and lightning trends have depicted a slight uptick in convective coverage and intensity. Recent CAM guidance also depicts a short-lived increase in storm coverage along the OH/PA/NY borders, before weakening in association with nocturnal cooling. Should storms organize and mature further, modest but adequate buoyancy (1000 J/kg MLCAPE, or 2000 J/kg MUCAPE) and deep-layer shear (30 knots bulk-effective shear) suggest that multicellular and transient supercellular structures may be achieved, with isolated, marginally severe hail and wind gusts possible. In addition, low-level speed and directional shear are present, with modest veering in the sfc-850 mb layer contributing to sickle-shaped hodographs and corresponding 150-200 m2/s2 effective SRH (per latest RAP forecast soundings), especially in western Pennsylvania. As such, a brief tornado cannot be ruled out in the near term, despite the slowly stabilizing environment. Nonetheless, given the expected isolated nature of the severe threat, a WW issuance is not anticipated. ..Squitieri/Edwards.. 09/01/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BUF...CTP...PBZ...RLX...CLE...ILN... LAT...LON 39838278 40258181 41498066 41948042 42277969 42427908 42187817 41677801 40627858 40047917 39698053 39448180 39838278 Read more

WW 0630 Status Updates
STATUS FOR WATCH 0630 HAS NOT BEEN ISSUED YET Read more

WW 630 SEVERE TSTM AZ 012235Z - 020600Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 630 NWS Storm Prediction Center Norman OK 335 PM MST Sun Sep 1 2019 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Central and western Arizona * Effective this Sunday afternoon and evening from 335 PM until 1100 PM MST. * Primary threats include... Scattered damaging winds and isolated significant gusts to 75 mph possible SUMMARY...Although isolated strong-severe storms already are occurring, the potential is increasing for one or two organized clusters to grow and send damaging to severe gusts westward across the deserts. The main threat area will be from that part of Pima County west of Tucson, northward across central Arizona, and the southern part of the I-17 corridor, westward to near the Colorado River. The severe thunderstorm watch area is approximately along and 105 statute miles east and west of a line from Prescott AZ to 75 miles south of Gila Bend AZ. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU0). 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. && 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 550. Mean storm motion vector 09035. ...Edwards Read more

No watches are valid as of Sun Sep 1 22:11:02 UTC 2019.

MD 1907 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PARTS OF SOUTHEAST MONTANA INTO EXTREME SOUTHWEST NORTH DAKOTA...FAR NORTHEAST WYOMING...WESTERN SOUTH DAKOTA...EXTREME NORTHWEST NEBRASKA
Mesoscale Discussion 1907 NWS Storm Prediction Center Norman OK 0509 PM CDT Sun Sep 01 2019 Areas affected...Parts of southeast Montana into extreme southwest North Dakota...far northeast Wyoming...western South Dakota...extreme northwest Nebraska Concerning...Severe potential...Watch unlikely Valid 012209Z - 020015Z Probability of Watch Issuance...5 percent SUMMARY...A couple storms may sustain themselves during the afternoon hours. Organized storms may pose a large hail and damaging wind threat. The very isolated coverage suggests that a WW issuance is not currently warranted. DISCUSSION...Isolated strong to severe storms have developed in Custer County, MT over the past hour or so, despite convection failing to become sustained earlier along the buoyancy axis (mainly along the WY/SD border). Peak afternoon heating and weak vertical ascent associated with a weak vorticity max cresting the ridge in western ND are supporting this more recent, successful attempt at convection. Should this storm or any other cell become established across the discussion area, ample instability (1500+ J/kg MLCAPE) and deep-layer shear (around 50 knots of bulk effective shear) is in place to foster the development of highly organized multicellular clusters or perhaps supercells. Given relatively steep mid-level lapse rates (7+ C/km), and potential for mid-level rotation, some of the more organized cells may produce large hail in addition to damaging wind gusts. Nonetheless, deep-layer ascent is quite weak across the area (as supported by the 12Z HREF and the last several runs of the HRRR), with low confidence in a substantial increase in convective coverage through the early evening hours. As such, a WW issuance is not anticipated. ..Squitieri/Edwards.. 09/01/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BIS...LBF...UNR...CYS...BYZ... LAT...LON 44340538 45750661 46400630 46410509 46080308 45700258 44700190 44130182 43330185 42870214 42770286 42950393 43320464 44340538 Read more

MD 1906 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR PARTS OF CENTRAL AND SOUTHERN ARIZONA
Mesoscale Discussion 1906 NWS Storm Prediction Center Norman OK 0334 PM CDT Sun Sep 01 2019 Areas affected...Parts of central and southern Arizona Concerning...Severe potential...Watch possible Valid 012034Z - 012230Z Probability of Watch Issuance...40 percent SUMMARY...Thunderstorms will continue to develop along the higher terrain of central and southeast Arizona this afternoon. Some of this will gradually consolidate, and may pose increasing risk for strong wind gusts, particularly south of the Mogollon Rim. It is not certain that a severe weather watch will be needed, but trends are being monitored for this possibility. DISCUSSION...Mid/upper support for convective development appears generally weak, but initiation of thunderstorm activity is ongoing, likely aided by daytime heating and orographic forcing along the Mogollon Rim and mountains of southeastern Arizona. Deep boundary layer mixing is also well underway across the lower deserts to the south and west, with sufficient moisture to support CAPE in excess of 1000 J/kg. Light deep-layer easterly ambient mean flow, with some enhancement at mid-levels, should at least contribute to some support for propagation of convection off the higher terrain, toward the lower deserts, through afternoon. This component seems strongest off the mountains of southeastern Arizona. However, the most substantive clustering of ongoing convection is currently along the Rim, south/southwest of Show Low. Within the next few hours, this may begin to produce increasing outflow advancing southwestward along and south of the Rim, where models suggest that the strongest low-level upslope flow component will become focused. This may be accompanied by continuing thunderstorm development and upscale convective growth, with increasing potential for localized strong downbursts, and strong wind gusts along the leading edge of the consolidating outflow. ..Kerr/Guyer.. 09/01/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TWC...FGZ...PSR... LAT...LON 32301129 32591189 32761208 33371285 34141316 34641147 33740996 33240980 32811007 32341050 32301129 Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Sun Sep 01 2019 Valid 012000Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. Little change was required to the previous outlook except to expand low tornado probabilities southwest to the Ohio River where significant low-level CAPE exists as per modified ILN 18Z sounding. Shear is weak, thus any rotation is expected to remain weak and short lived. ..Jewell.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1131 AM CDT Sun Sep 01 2019/ ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Sun Sep 01 2019 Valid 012000Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. Little change was required to the previous outlook except to expand low tornado probabilities southwest to the Ohio River where significant low-level CAPE exists as per modified ILN 18Z sounding. Shear is weak, thus any rotation is expected to remain weak and short lived. ..Jewell.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1131 AM CDT Sun Sep 01 2019/ ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Sun Sep 01 2019 Valid 012000Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. Little change was required to the previous outlook except to expand low tornado probabilities southwest to the Ohio River where significant low-level CAPE exists as per modified ILN 18Z sounding. Shear is weak, thus any rotation is expected to remain weak and short lived. ..Jewell.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1131 AM CDT Sun Sep 01 2019/ ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Sun Sep 01 2019 Valid 012000Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. Little change was required to the previous outlook except to expand low tornado probabilities southwest to the Ohio River where significant low-level CAPE exists as per modified ILN 18Z sounding. Shear is weak, thus any rotation is expected to remain weak and short lived. ..Jewell.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1131 AM CDT Sun Sep 01 2019/ ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0218 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EASTERN IDAHO... The forecast remains on track, with only minor changes needed with this forecast update to reflect the latest ensemble/deterministic guidance. See previous discussion below for more information. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 0125 AM CDT Sun Sep 01 2019/ ...Synopsis... A mature embedded impulse will traverse the northern Rockies along the crest of a fortified upper-level ridge on Day 2/Monday. Stronger flow aloft will glance the central/northern Rockies and northern Great Basin areas, inducing a surface mass response which will promote very breezy and dry conditions favorable for wildfire spread. ...Northern Great Basin into the central/northern Rockies... Widespread 15-20 mph sustained west-southwesterly winds, coincident with 10-20% RH, are expected to occur by afternoon across much of Wyoming, westward into Idaho and far southern Montana, and continue past sunset, where an elevated delineation was added. An additional downslope component of surface flow along the lee of the Bitterroot Range will also encourage sustained westerly winds of at least 20-25 mph (perhaps with higher gusts) across parts of the Snake River Plain, atop critically dry fuels, where a critical area was added. At least locally critical conditions may also be observed in terrain favoring locations east of the Snake River Plain into the Great Divide basin. However, the lack of widespread stronger flow across these areas lends too low of confidence to expand the critical area eastward at this time, though conditions will be monitored for a possible upgrade in later outlooks. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0218 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EASTERN IDAHO... The forecast remains on track, with only minor changes needed with this forecast update to reflect the latest ensemble/deterministic guidance. See previous discussion below for more information. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 0125 AM CDT Sun Sep 01 2019/ ...Synopsis... A mature embedded impulse will traverse the northern Rockies along the crest of a fortified upper-level ridge on Day 2/Monday. Stronger flow aloft will glance the central/northern Rockies and northern Great Basin areas, inducing a surface mass response which will promote very breezy and dry conditions favorable for wildfire spread. ...Northern Great Basin into the central/northern Rockies... Widespread 15-20 mph sustained west-southwesterly winds, coincident with 10-20% RH, are expected to occur by afternoon across much of Wyoming, westward into Idaho and far southern Montana, and continue past sunset, where an elevated delineation was added. An additional downslope component of surface flow along the lee of the Bitterroot Range will also encourage sustained westerly winds of at least 20-25 mph (perhaps with higher gusts) across parts of the Snake River Plain, atop critically dry fuels, where a critical area was added. At least locally critical conditions may also be observed in terrain favoring locations east of the Snake River Plain into the Great Divide basin. However, the lack of widespread stronger flow across these areas lends too low of confidence to expand the critical area eastward at this time, though conditions will be monitored for a possible upgrade in later outlooks. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0218 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EASTERN IDAHO... The forecast remains on track, with only minor changes needed with this forecast update to reflect the latest ensemble/deterministic guidance. See previous discussion below for more information. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 0125 AM CDT Sun Sep 01 2019/ ...Synopsis... A mature embedded impulse will traverse the northern Rockies along the crest of a fortified upper-level ridge on Day 2/Monday. Stronger flow aloft will glance the central/northern Rockies and northern Great Basin areas, inducing a surface mass response which will promote very breezy and dry conditions favorable for wildfire spread. ...Northern Great Basin into the central/northern Rockies... Widespread 15-20 mph sustained west-southwesterly winds, coincident with 10-20% RH, are expected to occur by afternoon across much of Wyoming, westward into Idaho and far southern Montana, and continue past sunset, where an elevated delineation was added. An additional downslope component of surface flow along the lee of the Bitterroot Range will also encourage sustained westerly winds of at least 20-25 mph (perhaps with higher gusts) across parts of the Snake River Plain, atop critically dry fuels, where a critical area was added. At least locally critical conditions may also be observed in terrain favoring locations east of the Snake River Plain into the Great Divide basin. However, the lack of widespread stronger flow across these areas lends too low of confidence to expand the critical area eastward at this time, though conditions will be monitored for a possible upgrade in later outlooks. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0218 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EASTERN IDAHO... The forecast remains on track, with only minor changes needed with this forecast update to reflect the latest ensemble/deterministic guidance. See previous discussion below for more information. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 0125 AM CDT Sun Sep 01 2019/ ...Synopsis... A mature embedded impulse will traverse the northern Rockies along the crest of a fortified upper-level ridge on Day 2/Monday. Stronger flow aloft will glance the central/northern Rockies and northern Great Basin areas, inducing a surface mass response which will promote very breezy and dry conditions favorable for wildfire spread. ...Northern Great Basin into the central/northern Rockies... Widespread 15-20 mph sustained west-southwesterly winds, coincident with 10-20% RH, are expected to occur by afternoon across much of Wyoming, westward into Idaho and far southern Montana, and continue past sunset, where an elevated delineation was added. An additional downslope component of surface flow along the lee of the Bitterroot Range will also encourage sustained westerly winds of at least 20-25 mph (perhaps with higher gusts) across parts of the Snake River Plain, atop critically dry fuels, where a critical area was added. At least locally critical conditions may also be observed in terrain favoring locations east of the Snake River Plain into the Great Divide basin. However, the lack of widespread stronger flow across these areas lends too low of confidence to expand the critical area eastward at this time, though conditions will be monitored for a possible upgrade in later outlooks. ...Please see www.spc.noaa.gov/fire for graphic product... Read more