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SPC Aug 17, 2024 2000 UTC Day 1 Convective Outlook

1 year 1 month ago

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Sat Aug 17 2024 Valid 172000Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CASCADES AND COLUMBIA BASIN...PARTS OF UTAH...AND IN THE OHIO/TENNESSEE VALLEYS... ...SUMMARY... Scattered severe thunderstorms are possible through tonight in vicinity of the Ohio Valley, Utah and the Cascades of Oregon and Washington. Wind and isolated hail are the primary threats. ...20z Update... The forecast remains largely on track with on minor changes. Strong to severe storms ongoing over the OH Valley and eastern US will remain capable of isolated damaging gusts through this evening. Scattered severe storms are also expected to develop over the Cascades and Columbia Basin later this afternoon and into the overnight hours with a risk for danging winds and hail. ...Tennessee Valley and southern Appalachians.... Multiple bands and clusters of strong to occasional severe storms are ongoing this afternoon ahead of the broad upper trough and slow moving cold front. Recent VAD observations from HTX and MRX show a belt of stronger mid-level flow has extend over parts of the eastern TN Valley and Southern Appalachians supporting greater deep-layer shear of 25-30 kt. Colocated with a hot and seasonably moist/unstable air mass, a cluster of more organized/robust convection being observed over part of northern AL and southern TN may continue east/southeast into parts of northern GA and the western Carolinas this afternoon/evening. A mix of persistent multi-cell clusters and transient supercell structures would support a risk for damaging winds and isolated hail. Have upgraded to level 2 categorical Slight to better account for the risk of damaging winds with this cluster of stronger storms. ...Utah... Ahead of a convective enhanced shortwave trough, scattered strong to severe thunderstorms should continue this afternoon and into the evening hours with a risk for damaging winds and occasional hail. Confidence in the highest threat corridor remains across parts of central UT where greater diurnal heating has allowed for moderate destabilization. The exact eastern extent of organized convective potential is somewhat nebulous given the limited buoyancy and expected degree of storm coverage. However, at least some risk for damaging gusts will be possible with high-based showers and storms over eastern UT. Have modified the eastern edge of the level-2 Slight Risk to better reflect the potential for organized storms with wind gust and hail potential later this afternoon. Otherwise, see the prior discussion for additional information. ..Lyons.. 08/17/2024 .PREV DISCUSSION... /ISSUED 1121 AM CDT Sat Aug 17 2024/ ...CA/OR/WA... Morning water vapor loop shows a strong and fast-moving shortwave trough approaching the coast of northern CA. This feature will rotate inland, affecting the Cascades region this afternoon and evening. Steep mid level lapse rates and pockets of MLCAPE of 500-1000 J/kg will aid in the development of scattered thunderstorms by early afternoon over the mountains and coastal ranges of northern CA, building quickly northward into southern/central OR. Winds aloft will be strenghtening during this period, allowing a few supercell storm structures to likely develop. These storms may pose a threat of large hail and locally damaging wind gusts through the afternoon as they track northward into WA. Other high-based storms capable of gusty/damaging winds may affect parts of the Columbia Basin of northern OR/central WA as well. ...UT... A compact shortwave trough over central NV will continue to rotate around the Four-Corners upper ridge into UT today. Considerable coverage of afternoon thunderstorms will likely accompany this system. Winds aloft will be relatively strong, favoring faster-moving organized multicell or occasional supercell structures capable of damaging winds and hail. One forecast uncertainty is the extent of morning cloudiness and its impact on afternoon destabilization. Regardless, at least isolated severe storms are expected, with some threat spreading into southwest WY by evening. ...Eastern US... A broad upper trough will affect much of the eastern US today, with clusters of thunderstorms from NY/PA across the Appalachians into the Mid South. Any of these clusters may occasionally pose a risk of locally gusty/damaging wind gusts or hail. However, perhaps a more focused area of concern will extend from northern TN into southern OH. The axis of the mid level speed max (~40 knots) will spread across this area during the afternoon. CAM guidance has been consistent on suggesting a higher confidence in a few intense cells in this region. Read more