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SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0500 PM CDT Sun Jun 30 2024 Valid 021200Z - 081200Z Mid-level ridging is forecast to amplify significantly over the Pacific Coast through the extended forecast period. As the ridge builds, stronger flow aloft will be shunted to the northeast over parts of the Great Basin and northern Rockies through much of next week. While several perturbations will pass along the eastern periphery of the ridge, much of the Southwest will see extreme heat and dry conditions persist. Fire-weather concerns should increase through the period, especially as the upper ridge breaks down next weekend. ...Great Basin and Southwest... With ridge building through the first part of the extended period, very warm and dry surface conditions are likely to develop across parts of the Southwest. However, much of the stronger flow will remain displaced to the northeast, keeping surface winds modest through the first part of the work week. A slight increase in wind speeds is possible D4/Wed behind a dry cold front over parts of the northern Great Basin. 15-20 mph gusts and afternoon humidity of 10-20% could support several hours of near-critical fire-weather conditions within dry fuels. Flow aloft should weaken again toward the end of the week as the ridge temporarily strengthens. However, heading into the weekend, another weak trough should pass east of the ridge, potentially increasing dry and windy conditions over the Southwest. Through the reminder of the weekend into week 2, most guidance shows a decrease in ridge strength with a possible pattern shift toward western US troughing. Confidence in the result of this transition period remains very low as multiple model solutions are present. Some guidance shows an increase in showers and thunderstorm potential with increasing mid-level moisture, while others show a more substantial increase in hot, dry and windy conditions post ridging. Regardless of the outcome, an increase in fire-weather potential is very likely over parts of the Great Basin and Southwest, owing to the antecedent hot and dry period followed by ridge break down. ...CA... Beneath the upper ridge, extreme heat is expected over much of CA and the West Coast this week and into the weekend. While background winds should remain light, a low-level thermal trough may locally enhance dry and windy conditions across the northern and central parts of the state. A period of somewhat stronger northerly Sundowner winds may also develop D5/Thur into D6/Friday over southwest CA behind the weak trough passing to the east. While uncertain, locally higher fire-weather concerns could develop. ..Lyons.. 06/30/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0500 PM CDT Sun Jun 30 2024 Valid 021200Z - 081200Z Mid-level ridging is forecast to amplify significantly over the Pacific Coast through the extended forecast period. As the ridge builds, stronger flow aloft will be shunted to the northeast over parts of the Great Basin and northern Rockies through much of next week. While several perturbations will pass along the eastern periphery of the ridge, much of the Southwest will see extreme heat and dry conditions persist. Fire-weather concerns should increase through the period, especially as the upper ridge breaks down next weekend. ...Great Basin and Southwest... With ridge building through the first part of the extended period, very warm and dry surface conditions are likely to develop across parts of the Southwest. However, much of the stronger flow will remain displaced to the northeast, keeping surface winds modest through the first part of the work week. A slight increase in wind speeds is possible D4/Wed behind a dry cold front over parts of the northern Great Basin. 15-20 mph gusts and afternoon humidity of 10-20% could support several hours of near-critical fire-weather conditions within dry fuels. Flow aloft should weaken again toward the end of the week as the ridge temporarily strengthens. However, heading into the weekend, another weak trough should pass east of the ridge, potentially increasing dry and windy conditions over the Southwest. Through the reminder of the weekend into week 2, most guidance shows a decrease in ridge strength with a possible pattern shift toward western US troughing. Confidence in the result of this transition period remains very low as multiple model solutions are present. Some guidance shows an increase in showers and thunderstorm potential with increasing mid-level moisture, while others show a more substantial increase in hot, dry and windy conditions post ridging. Regardless of the outcome, an increase in fire-weather potential is very likely over parts of the Great Basin and Southwest, owing to the antecedent hot and dry period followed by ridge break down. ...CA... Beneath the upper ridge, extreme heat is expected over much of CA and the West Coast this week and into the weekend. While background winds should remain light, a low-level thermal trough may locally enhance dry and windy conditions across the northern and central parts of the state. A period of somewhat stronger northerly Sundowner winds may also develop D5/Thur into D6/Friday over southwest CA behind the weak trough passing to the east. While uncertain, locally higher fire-weather concerns could develop. ..Lyons.. 06/30/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

WW 0490 Status Updates
STATUS REPORT ON WW 490 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NNW EEN TO 10 ESE AUG TO 50 S HUL. ..WEINMAN..06/30/24 ATTN...WFO...GYX...CAR...BTV... STATUS REPORT FOR WS 490 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MEC001-005-009-013-015-023-027-029-031-302240- ME . MAINE COUNTIES INCLUDED ARE ANDROSCOGGIN CUMBERLAND HANCOCK KNOX LINCOLN SAGADAHOC WALDO WASHINGTON YORK NHC001-005-011-013-015-017-019-302240- NH . NEW HAMPSHIRE COUNTIES INCLUDED ARE BELKNAP CHESHIRE HILLSBOROUGH MERRIMACK ROCKINGHAM STRAFFORD SULLIVAN ANZ050-051-052-150-151-152-153-154-302240- CW . ADJACENT COASTAL WATERS INCLUDED ARE Read more

WW 0490 Status Updates
STATUS REPORT ON WW 490 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NNW EEN TO 10 ESE AUG TO 50 S HUL. ..WEINMAN..06/30/24 ATTN...WFO...GYX...CAR...BTV... STATUS REPORT FOR WS 490 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MEC001-005-009-013-015-023-027-029-031-302240- ME . MAINE COUNTIES INCLUDED ARE ANDROSCOGGIN CUMBERLAND HANCOCK KNOX LINCOLN SAGADAHOC WALDO WASHINGTON YORK NHC001-005-011-013-015-017-019-302240- NH . NEW HAMPSHIRE COUNTIES INCLUDED ARE BELKNAP CHESHIRE HILLSBOROUGH MERRIMACK ROCKINGHAM STRAFFORD SULLIVAN ANZ050-051-052-150-151-152-153-154-302240- CW . ADJACENT COASTAL WATERS INCLUDED ARE Read more

WW 0490 Status Updates
STATUS REPORT ON WW 490 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NNW EEN TO 10 ESE AUG TO 50 S HUL. ..WEINMAN..06/30/24 ATTN...WFO...GYX...CAR...BTV... STATUS REPORT FOR WS 490 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MEC001-005-009-013-015-023-027-029-031-302240- ME . MAINE COUNTIES INCLUDED ARE ANDROSCOGGIN CUMBERLAND HANCOCK KNOX LINCOLN SAGADAHOC WALDO WASHINGTON YORK NHC001-005-011-013-015-017-019-302240- NH . NEW HAMPSHIRE COUNTIES INCLUDED ARE BELKNAP CHESHIRE HILLSBOROUGH MERRIMACK ROCKINGHAM STRAFFORD SULLIVAN ANZ050-051-052-150-151-152-153-154-302240- CW . ADJACENT COASTAL WATERS INCLUDED ARE Read more

WW 490 SEVERE TSTM ME NH VT CW 301650Z - 010000Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 490 NWS Storm Prediction Center Norman OK 1250 PM EDT Sun Jun 30 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Maine New Hampshire Eastern Vermont Coastal Waters * Effective this Sunday afternoon and evening from 1250 PM until 800 PM EDT. * Primary threats include... Scattered damaging wind gusts to 70 mph likely Isolated large hail events to 1.5 inches in diameter possible A tornado or two possible SUMMARY...Thunderstorms are expected to intensify this afternoon while moving quickly eastward. Scattered severe/damaging winds up to 60-70 mph should be the main threat, but isolated hail around 1-1.5 inches in diameter may occur with any supercell. A brief tornado also appears possible. The severe thunderstorm watch area is approximately along and 60 statute miles east and west of a line from 25 miles north northwest of Caribou ME to 20 miles southwest of Portsmouth NH. 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. && OTHER WATCH INFORMATION...CONTINUE...WW 489... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27040. ...Gleason Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 SSW HGR TO 25 SSE AVP TO 20 E MSV TO 10 S CON. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1496 ..WEINMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302240- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302240- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302240- MA . MASSACHUSETTS COUNTIES INCLUDED ARE Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 SSW HGR TO 25 SSE AVP TO 20 E MSV TO 10 S CON. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1496 ..WEINMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302240- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302240- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302240- MA . MASSACHUSETTS COUNTIES INCLUDED ARE Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 SSW HGR TO 25 SSE AVP TO 20 E MSV TO 10 S CON. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1496 ..WEINMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302240- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302240- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302240- MA . MASSACHUSETTS COUNTIES INCLUDED ARE Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 SSW HGR TO 25 SSE AVP TO 20 E MSV TO 10 S CON. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1496 ..WEINMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302240- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302240- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302240- MA . MASSACHUSETTS COUNTIES INCLUDED ARE Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 SSW HGR TO 25 SSE AVP TO 20 E MSV TO 10 S CON. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1496 ..WEINMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302240- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302240- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302240- MA . MASSACHUSETTS COUNTIES INCLUDED ARE Read more

WW 489 SEVERE TSTM CT DE MA NJ NY PA RI CW 301510Z - 302300Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 489 NWS Storm Prediction Center Norman OK 1110 AM EDT Sun Jun 30 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Connecticut Northern Delaware Massachusetts New Jersey Southern New York Central and Eastern Pennsylvania Rhode Island Coastal Waters * Effective this Sunday morning and evening from 1110 AM until 700 PM EDT. * Primary threats include... Widespread damaging winds likely with isolated significant gusts to 75 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...A mix of thunderstorm clusters and supercells should pose a threat for numerous to widespread severe/damaging winds as they move eastward this afternoon and evening. Peak wind gusts should generally range around 60-70 mph, with isolated gusts perhaps reaching up to 75 mph. Occasional hail around 1-1.5 inches in diameter may also occur with any sustained supercell. The severe thunderstorm watch area is approximately along and 100 statute miles east and west of a line from 35 miles north northwest of Worcester MA to 30 miles west southwest of Philadelphia PA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU9). 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 1.5 inches. Extreme turbulence and surface wind gusts to 65 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27035. ...Gleason Read more

WW 489 SEVERE TSTM CT DE MA NJ NY PA RI CW 301510Z - 302300Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 489 NWS Storm Prediction Center Norman OK 1110 AM EDT Sun Jun 30 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Connecticut Northern Delaware Massachusetts New Jersey Southern New York Central and Eastern Pennsylvania Rhode Island Coastal Waters * Effective this Sunday morning and evening from 1110 AM until 700 PM EDT. * Primary threats include... Widespread damaging winds likely with isolated significant gusts to 75 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...A mix of thunderstorm clusters and supercells should pose a threat for numerous to widespread severe/damaging winds as they move eastward this afternoon and evening. Peak wind gusts should generally range around 60-70 mph, with isolated gusts perhaps reaching up to 75 mph. Occasional hail around 1-1.5 inches in diameter may also occur with any sustained supercell. The severe thunderstorm watch area is approximately along and 100 statute miles east and west of a line from 35 miles north northwest of Worcester MA to 30 miles west southwest of Philadelphia PA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU9). 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 1.5 inches. Extreme turbulence and surface wind gusts to 65 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27035. ...Gleason Read more

WW 0492 Status Updates
STATUS FOR WATCH 0492 HAS NOT BEEN ISSUED YET Read more

MD 1493 CONCERNING SEVERE THUNDERSTORM WATCH 490... FOR PORTIONS OF MAINE INTO NEW HAMPSHIRE
Mesoscale Discussion 1493 NWS Storm Prediction Center Norman OK 0221 PM CDT Sun Jun 30 2024 Areas affected...portions of Maine into New Hampshire Concerning...Severe Thunderstorm Watch 490... Valid 301921Z - 302115Z The severe weather threat for Severe Thunderstorm Watch 490 continues. SUMMARY...Severe thunderstorms producing strong/damaging gusts remain possible across southern New Hampshire into coastal and Down East Maine. DISCUSSION...The strongest convection ongoing this afternoon is along a pre-frontal surface trough and within the axis of greater instability and low-level moisture. A line of strong to severe storms producing wind damaging will continue to shift east/southeast across Down East Maine the next couple of hours. Additional more isolated convection is ongoing across New Hampshire and will shift into coastal Maine, also posing a damaging wind risk. Additional storms may move into northern Maine in association with the synoptic cold front. However, cooler temperatures and lower dewpoints are resulting in weaker instability with northward extent, and severe potential will be a bit lower compared to further south. ..Leitman.. 06/30/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...CAR...GYX...BOX...ALY... LAT...LON 44187148 46256775 46016720 45236687 44656698 43206925 42817082 42737191 42817247 43357238 43887210 44187148 Read more

WW 0491 Status Updates
STATUS REPORT ON WW 491 THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA. ..LEITMAN..06/30/24 ATTN...WFO...LWX...PHI...AKQ...RAH...RNK... STATUS REPORT FOR WS 491 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS DEC001-005-302140- DE . DELAWARE COUNTIES INCLUDED ARE KENT SUSSEX DCC001-302140- DC . DISTRICT OF COLUMBIA COUNTIES INCLUDED ARE DISTRICT OF COLUMBIA MDC003-005-009-011-013-015-017-019-021-025-027-029-031-033-035- 037-039-041-045-047-510-302140- MD . MARYLAND COUNTIES INCLUDED ARE ANNE ARUNDEL BALTIMORE CALVERT CAROLINE CARROLL CECIL CHARLES DORCHESTER FREDERICK HARFORD HOWARD KENT Read more

WW 0491 Status Updates
STATUS REPORT ON WW 491 THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA. ..LEITMAN..06/30/24 ATTN...WFO...LWX...PHI...AKQ...RAH...RNK... STATUS REPORT FOR WS 491 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS DEC001-005-302140- DE . DELAWARE COUNTIES INCLUDED ARE KENT SUSSEX DCC001-302140- DC . DISTRICT OF COLUMBIA COUNTIES INCLUDED ARE DISTRICT OF COLUMBIA MDC003-005-009-011-013-015-017-019-021-025-027-029-031-033-035- 037-039-041-045-047-510-302140- MD . MARYLAND COUNTIES INCLUDED ARE ANNE ARUNDEL BALTIMORE CALVERT CAROLINE CARROLL CECIL CHARLES DORCHESTER FREDERICK HARFORD HOWARD KENT Read more

WW 0490 Status Updates
STATUS REPORT ON WW 490 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 WNW EEN TO 30 E BML TO 30 SE HUL. ..LEITMAN..06/30/24 ATTN...WFO...GYX...CAR...BTV... STATUS REPORT FOR WS 490 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MEC001-005-009-011-013-015-019-023-027-029-031-302140- ME . MAINE COUNTIES INCLUDED ARE ANDROSCOGGIN CUMBERLAND HANCOCK KENNEBEC KNOX LINCOLN PENOBSCOT SAGADAHOC WALDO WASHINGTON YORK NHC001-003-005-011-013-015-017-019-302140- NH . NEW HAMPSHIRE COUNTIES INCLUDED ARE BELKNAP CARROLL CHESHIRE HILLSBOROUGH MERRIMACK ROCKINGHAM STRAFFORD SULLIVAN ANZ050-051-052-150-151-152-153-154-302140- CW Read more

WW 0489 Status Updates
STATUS REPORT ON WW 489 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 5 S HGR TO 25 SSE AVP TO 10 NNE MSV TO 25 W EEN. ..LEITMAN..06/30/24 ATTN...WFO...OKX...BOX...ALY...PHI...BGM...CTP... STATUS REPORT FOR WS 489 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-302140- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM DEC003-302140- DE . DELAWARE COUNTIES INCLUDED ARE NEW CASTLE MAC003-005-009-011-013-015-017-021-023-025-027-302140- MA . MASSACHUSETTS COUNTIES INCLUDED ARE BERKSHIRE BRISTOL ESSEX FRANKLIN HAMPDEN HAMPSHIRE Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Sun Jun 30 2024 Valid 302000Z - 011200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN NEW ENGLAND AND THE EASTERN MID-ATLANTIC... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN HIGH PLAINS... ...SUMMARY... Scattered to numerous damaging wind gusts are likely across parts of the Northeast and Mid-Atlantic States this afternoon and evening. Large hail and severe/damaging winds should also occur from southern Montana into western North Dakota. ...20Z Update... The primary change with this update was to trim severe-thunderstorm probabilities in the Northeast behind an eastward-advancing cold front. Ahead of the front, clusters of organized storms continue tracking eastward from the Northeast into the eastern Mid-Atlantic states, with the primary risk being damaging winds. For additional details, reference Mesoscale Discussions 1492/1493 and Severe Thunderstorm Watches 489/490/491. Within the broad Marginal Risk over the northern and central High Plains, there may be a slightly more focused corridor of severe-thunderstorm potential along/immediately east of the Colorado Front Range. Around 40 kt of effective shear amid a moderately unstable air mass will conditionally support a couple supercells capable of large hail, before growing locally upscale and tracking eastward. A small Slight Risk was considered, though weak large-scale ascent and the potentially localized threat cast uncertainty on the overall severe risk -- precluding an upgrade. ..Weinman/Jewell.. 06/30/2024 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Jun 30 2024/ ...Northeast/Mid-Atlantic into the Carolinas... A mid-level trough over the Great Lakes and eastern Canada will continue moving eastward through the period. An associated cold front will likewise advance east-southeastward across New England and much of the Mid-Atlantic through this evening. Based on area 12Z soundings and recent surface observations, a very moist airmass is in place ahead of the front, with surface dewpoints generally in the low to mid 70s. Filtered daytime heating with broken cloud cover will support weak to moderate instability through late this afternoon, with most guidance continuing to suggest a narrow corridor of 1000-2000 J/kg MLCAPE will be in place along/near the I-95 corridor from southern New England to the eastern Mid-Atlantic. Mid-level flow will increase through the day in tandem with the upper trough, which will foster strong deep-layer shear and organized convection. Expectations are for thunderstorms to continue increasing in coverage and intensity this afternoon, both along/ahead of the cold front and a pre-frontal surface trough. Multiple rounds of intense convection appear possible. Given a rather favorable thermodynamic and kinematic parameter space, swaths of severe/damaging winds generally 60-70 mph will likely occur as a mix of bowing line segments/clusters and a few supercells sweep eastward through the afternoon/evening. No changes have been made to the Enhanced Risk across parts of southern New England into the Mid-Atlantic, where the greatest concentration of damaging winds is still anticipated. Isolated hail and perhaps a tornado may also occur with any sustained supercell, although poor mid-level lapse rates and modest/veered low-level flow should hinder both of these threats, respectively. Deep-layer shear will be weaker with southward extent across the Mid-Atlantic into the Carolinas. Convective mode should also tend to be mainly multicellular across these regions. Even so, steepened low-level lapse rates and ample instability should support a threat for scattered damaging winds as thunderstorms develop and spread eastward to the Atlantic Coast this afternoon/evening. ...Northern/Central High Plains... A mid-level shortwave trough evident over the Northwest this morning will progress eastward across the northern Rockies and adjacent High Plains through tonight. A surface lee cyclone is forecast to deepen and consolidate over northern WY/southeast MT by this evening, as large-scale ascent preceding the upper trough overspreads the northern High Plains. Even though low-level moisture is expected to remain rather limited across this area, steep lapse rates and daytime heating will contribute to at least weak instability developing by late afternoon. Moderate to strong deep-layer shear will support updraft organization. Cellular convection that initially develops over the higher terrain of southwest MT and vicinity should quickly grow upscale into a small bowing cluster as it moves east-northeastward across central/eastern MT this evening. Large hail may occur initially, but a transition to mainly a severe/damaging wind threat appears likely as this mode transition occurs. Isolated significant severe wind gusts (75-80 mph) appear possible given the very steep/favorable low/mid-level lapse rates expected. This wind threat may continue into parts of western ND and vicinity tonight before convection eventually weakens. Farther south, isolated to scattered thunderstorms should develop along/east of the higher terrain from WY into CO. Various NAM/RAP forecast soundings across this area show favorable shear for organized convection, including the potential for a mix of multicells and perhaps a couple of supercells. The southern fringe of the stronger mid-level flow and the northwest edge of the monsoonal moisture may overlap enough in western CO to support an isolated threat for severe wind gusts. ...Arizona... Low/mid-level moisture should gradually increase through the period on the western periphery of a mid/upper-level high centered over the southern Plains. Diurnal heating in the wake of overnight convection should occur across the higher terrain of eastern/southeast AZ through this afternoon, which will aid in the development of weak to moderate instability. Expectations are for thunderstorms to initially form over the higher terrain, and then slowly westward late this afternoon and evening in response to around 15-20 kt of east-southeasterly mid-level flow. A very well mixed boundary layer, with steep lapse rates through much of the troposphere, should support a threat for isolated strong to severe wind gusts with this high-based convection. Read more