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Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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161 ACUS01 KWNS 300548 SWODY1 SPC AC 300547 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1247 AM CDT Sun Jun 30 2024 Valid 301200Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FROM EASTERN AND SOUTHERN NEW ENGLAND INTO THE MID-ATLANTIC...AND THIS EVENING INTO EARLY TONIGHT ACROSS MT... ...SUMMARY... Scattered damaging winds will be possible across parts of the Northeast and Mid-Atlantic States this afternoon/evening. Hail and damaging winds may also occur from eastern Montana into western North Dakota. ...New England into the Mid-Atlantic this afternoon/evening... A midlevel shortwave trough over Lower MI will progress eastward toward NY/PA by early tonight, while an associated surface cold front moves eastward across New England and southeastward across the central Appalachians. A corridor of boundary-layer dewpoints in the low 70s and surface heating in cloud breaks will support diurnal destabilization ahead of the cold front/pre-frontal trough which will focus thunderstorm development by early-mid afternoon. Though midlevel lapse rates will not be particularly steep, MLCAPE is expected to increase to 1500-2000 J/kg as midlevel flow also increases with largely straight, but sufficiently long hodographs. The net result will be a favorable environment favorable for organized storm clusters/line segments, as well as a few supercells, capable of producing damaging winds, isolated large hail and perhaps a tornado into the evening across southern and eastern New England. Deep-layer vertical shear will weaken with southwestward extent into VA/NC, where the storm mode is expected be predominately multicell clusters. Still, thermodynamic profiles will support the potential for occasional wind damage with downbursts. ...Northern/central High Plains this evening into tonight... A midlevel shortwave trough over WA/OR will move eastward over the northern Rockies by tonight, with downstream lee cyclogenesis expected across WY/MT. Though the richer low-level moisture will be confined to KS southward along a baroclinic zone, there will be a modest increase in low-level moisture across the central/northern High Plains on southeasterly low-level flow. The somewhat larger buoyancy and weaker convective inhibition are expected closer to the high terrain, with the more likely area for storm-cluster development over the mountains of southern MT in the zone of ascent preceding the midlevel trough. The storms will subsequently spread east-northeastward toward eastern MT with an accompanying threat for severe outflow winds of 60-70 mph. Large hail (mainly 1-1.75 inches in diameter) will also be possible with any embedded supercell structures. Farther south, isolated thunderstorm development will be possible immediately east of the higher terrain from WY into CO. Forecast wind profiles will be at least marginally favorable for supercells, though storm coverage is in question. The southern fringe of the stronger midlevel flow and the northwest edge of the monsoonal moisture plume may support an isolated wind-damage threat into western CO. ...Southern AZ this afternoon/evening... Around the southwestern periphery of a midlevel high over the southern Plains, low-midlevel moisture has been gradually increasing from southern NM into AZ. In the wake of scattered overnight storms, cloud breaks will allow surface heating/destabilization across southeast/south central AZ into the afternoon, which will drive moderate buoyancy (MLCAPE up to 1000 J/kg). Convection will form over the high terrain of southeast AZ and spread westward through late afternoon/evening in response to east-southeasterly midlevel flow of 20-25 kt. A typical/deep mixed boundary layer coupled with the moderate buoyancy will support a few strong outflow gusts (50-60 mph) with precipitation-loaded downdrafts. ..Thompson/Squitieri.. 06/30/2024 $$