Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 12 2023 20:01:14 ACUS01 KWNS 122001 SWODY1 SPC AC 121959 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Sat Aug 12 2023 Valid 122000Z - 131200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST OHIO INTO PENNSYLVANIA AND WESTERN/SOUTHERN NEW YORK... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE GREAT PLAINS... ....SUMMARY... The most concentrated area of severe-thunderstorm threats into evening extends from northeast Ohio across parts of Pennsylvania and into central New York, with damaging to severe wind expected, along with large hail and a few tornadoes. Other severe storms capable of large hail and/or damaging gusts are possible across parts of the Great Plains into this evening. ....Great Lakes/Northeast area... The main changes for this area were to expand the Slight (level 2 of 5) and Marginal (level 1 of 5) risk areas southward a small amount across the New Jersey vicinity. This is to account for latest trends in observations and CAMs guidance. Otherwise, scattered severe storms continue across Tornado Watch 634 from northern OH into PA and western/central NY. Reference forthcoming MCD 1969 for short term severe potential. ....Mid-South and OH/TN Valley vicinity... Risk probabilities have been trimmed from portions of southeast MO/northeast AR into western/Middle TN and western/central KY where airmass modification by earlier convection has resulted in widespread MLCINH. Severe potential is expected to remain low across these areas the remainder of the period. ....Southern Appalachians/Carolinas... The Slight (level 2 of 5) risk has been trimmed across parts of TN/AL behind ongoing convective clusters. However, severe potential is expected to persist eastward into western/west-central NC/SC through this evening. Damaging gusts will be the main hazard expected with forward-propagating clusters. As a result, severe probabilities have been expanded eastward, with a gradual weakening trend expected as storms move into central NC/SC. ....SD/NE... A Slight risk (level 2 of 5) has been added to portions of southwest SD into north-central NE. Latest CAMs guidance suggest isolated supercells capable of large hail will develop and move east/southeast off the Black Hills late this afternoon/evening. Boundary-layer moisture will remain somewhat modest but will continue to increase through the evening, aiding in continued destabilization. With time, convection may grow upscale into a small bow as it tracks near the SD/NE border. This process should be aided by an increasing southerly low-level jet this evening. A few damaging/severe gusts may accompany this activity. Reference MCD 1968 for short term severe information. ....Southern Plains... The Marginal (level 1 of 2) risk has been expanded southward a small amount across OK. A differential heating zone and outflow from prior convection is oriented across the region and visible satellite and current radar indicate a band of developing storms from the southern TX Panhandle into southwest and central OK. Damaging gusts will be the main concern with this activity given generally weak vertical shear and a deeply mixed boundary-layer across the hot side of the differential heating zone. See MCD 1967 for more details in short term severe potential across the southern High Plains. ...Leitman.. 08/12/2023 ..PREV DISCUSSION... /ISSUED 1123 AM CDT Sat Aug 12 2023/ ....Southern Great Lakes into the Northeast... Water-vapor imagery this morning shows a mid-level shortwave trough moving across the northern Great Lakes with a belt of stronger flow moving through the southern Great Lakes. Scattered thunderstorms will likely continue to develop through midday into the afternoon with the stronger storms becoming capable of a hail/wind threat. Forecast soundings show some low-level hodograph curvature, especially with northeast extent from northeast OH into PA and NY. Supercells will likely evolve from the stronger updrafts and pose a large to very large hail threat. It is with the supercells from the northern half of PA/northeast OH into southern NY where a tornado risk will seemingly focus this afternoon. As a surface cold front pushes east, additional storms are possible along the front and some of these will probably have an attendant hail/wind risk before weakening this evening. ....South-central Great Plains... In agreement with the previously issued forecast, expected widely scattered to scattered thunderstorms to initially develop over the eastern slopes of the Sangre de Cristos into the Raton Mesa region, and perhaps over intensely heated Plains areas of the northwestern TX Panhandle and northeastern NM. Activity then should move eastward and coalesce into one or more complexes, with severe wind the main concern, and isolated large hail possible. Upscale growth will probably occur during the evening with the severe wind risk spreading from southeastern CO and the OK/ northern TX Panhandles across southern KS and northern OK as it moves into richer moisture and large CAPE. In KS/OK, severe-gust potential should decrease with eastward extent tonight as activity encounters a gradually stabilizing boundary layer, but uncertainty exists over cold-pool strength vs. CINH and how fast the threat will diminish. ....TN Valley/Southeast... An ongoing thunderstorm cluster over KY/TN will continue to move east-southeast with scattered to numerous thunderstorms expected in the area centered over the TN Valley. Widespread 3000-4000 J/kg MLCAPE in areas slightly removed from ongoing midday storms will favor the potential for clusters to be capable of strongly water-loaded downdrafts. Damaging to locally severe gusts will be the main concern. ....North-central Plains... Isolated to scattered thunderstorms should develop this afternoon near the Black Hills vicinity. Supercells are possible given the strength of deep-layer shear. Isolated severe gusts and hail will be possible. This activity will diminish overnight and with southeastward extent, as the inflow layer stabilizes and becomes more elevated. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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