Administrators NorthGeorgiaWX Posted August 2 Administrators Posted August 2 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Fri Aug 02 2024 Valid 021300Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE OHIO VALLEY AND SOUTHERN APPALACHIANS EASTWARD TO THE ATLANTIC SEABOARD...AND IN PARTS OF THE CENTRAL HIGH PLAINS AND SOUTHEAST ARIZONA... ...SUMMARY... Strong to isolated severe thunderstorm gusts are possible today from the Ohio Valley and southern Appalachians eastward to the Atlantic Seaboard, and in parts of the central High Plains and southeast Arizona. ...Synopsis... In mid/upper levels, the pattern over the CONUS will be dominated by a large anticyclone in the West, centered over the Four Corners region, and troughing in the Great Lakes region. A well-developed, compact cyclone was centered over northwestern IN, along a trough extending from Lake Huron to northeastern AR. The cyclone should pivot eastward today and weaken somewhat, probably devolving back to a vorticity lobe within a strong open-wave trough at or soon after 00Z. At 00Z, that trough should extend from southern ON through the remnant low across northern/western OH, to the Tennessee Valley region. By 12Z, the trough should reach an axis near BUF-ZZV-LOZ-BHM. Well to the southwest and past the mid/upper-level high, the northern part of a trough extending to the tropical Pacific near T.S. Carlotta was noted in moisture-channel imagery over portions of southern CA and the Channel Islands. That portion of the longer trough should break off north-northwestward along the southern/ central CA Coast through the period. At the surface, 11Z analysis showed a cold front extending from a low near TOL southwestward across western IN, southern IL, southeastern MO, northern AR, central OK, the TX Panhandle, and east-central NM. By 00Z, the front should extend from a diffuse low over eastern OH across eastern parts of KY/TN to northern MS, southern AR, and parts of north-central/northwest TX, with a prefrontal trough from eastern PA to west-central NC. By 12Z, the front should reach eastern parts of NY/PA, to northern AL, becoming quasistationary from there across northern MS and north TX. ...Eastern CONUS... Height falls and difluent flow aloft will spread across a large part of the East from the Appalachians eastward, ahead of the progressive mid/upper trough and associated surface cold front. Isolated to scattered thunderstorms should form through the afternoon along/ ahead of the front, along the prefrontal trough, over favored higher elevations, and along outflow/differential-heating boundaries, all in rich low-level moisture and diurnally weakening ambient MLCINH. Where the combination of diurnal heating and boundary-layer moisture is greatest -- over portions of the Piedmont and coastal plain of the Carolinas (18-19 g/kg mean mixing ratio in the 12Z CHS sounding) and separately over northern parts of MS/AL -- 3000-3500 J/kg MLCAPE may be generated. Around 1500-2500 J/kg values are expected over most of the rest of the outlook area. Large-scale ascent aloft also will increase ahead of the mid/upper trough, though stronger winds aloft and deep shear should lag the cold front. The lack of greater shear should keep activity multicellular, with strong to isolated severe pulse-type gust potential being the main concern. ...Central High Plains... Isolated to scattered thunderstorms are expected to form during mid/late afternoon over the Laramie Range, Cheyenne Ridge and nearby portions of southeastern WY, northeastern CO and the NE Panhandle. Activity should move southeastward toward a meridionally aligned moist axis over western parts of KS/NE and atop strong boundary- layer heating/mixing, with enough remaining moisture west of the axis to support 500-1000 J/kg MLCAPE, atop DCAPE values about twice that. Though deep-layer flow will be modest, strong veering with height will yield 30-35 kt effective-shear magnitudes, supporting some multicellular organization and potential for upscale growth for a few hours. Thunderstorms should move generally southeastward and remain high-based, offering isolated severe gusts and marginal hail until convection weakens in stabilizing air this evening. ...Portions of southern AZ... Isolated to scattered thunderstorms are expected to form this afternoon, mainly over higher elevations of the various mountain ranges on either side of the international border, and Mogollon Rim. The greatest potential for damaging to isolated severe gusts should be over portions of southeastern AZ, and south-central areas near the border, where mature cells can move over deep boundary layers characterized by hot antecedent surface temperatures, sufficient moisture to maintain 500-1500 J/kg MLCAPE (locally/briefly higher), and steep, nearly dry-adiabatic lapse rates. As the southern CA trough moves away from the area, midlevel winds around the anticyclone should be predominantly southeasterly across this region, encouraging cell motions toward the west through northwest. Coverage and potential for wind-enhancing clustering will be limited by a lack of robust mid/upper-level support behind the trough aloft, but the most vigorous cells should pose a local risk of severe gusts. ..Edwards/Grams.. 08/02/2024 Read more View the full article Quote
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