Storm Prediction Center Day 4-8 Severe Weather Outlook Page (2024)

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 ZCZC SPCSWOD48 ALL ACUS48 KWNS 210904 SPC AC 210904 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0404 AM CDT Tue May 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Day 4/Fri - Mid MS Valley/Upper Great Lakes vicinity... An upper shortwave trough over the northern Plains will pivot northeast across the Upper Midwest on Friday. At the surface, low pressure will develop northward across MN/WI and a trailing cold front will push east, becoming positioned from WI to central OK/MO by Saturday morning. Some severe potential is possible ahead of the front from the Mid-MS Valley into the Great Lakes vicinity. However, ongoing convection early Friday and large-scale ascent lifting northeast of the region with time is resulting in uncertainty. Severe probabilities will likely be needed in subsequent outlooks as mesoscale details become better resolved, but confidence is too low to delineate an unconditional 15 percent probability at this time. ...Day 5/Sat - Southern Plains to the Ozarks vicinity... Low-amplitude west/southwest mid/upper flow is forecast across the southern Plains to the Mid-South vicinity for much of the diurnal period on Saturday. By 00z, forecast guidance suggests a shortwave trough will eject from the southern Rockies into the southern Plains, and eventually impinging on the Ozarks/Mid-South area by Sunday morning. A very moist and unstable airmass is forecast over the southern Plains vicinity ahead of this feature as a surface warm front lifts northward through the day. Increasing ascent may not arrive until after 00-03z, limiting convective initiation until the nighttime hours. If storms can develop during the day across portions of OK/TX, all hazards severe potential will exist. Otherwise, thunderstorm potential may be more likely during the evening/overnight from north TX into southeast OK and AR as large-scale ascent increases and a 65-75 kt 500 mb jet overspreads the region. The north and west bounds of severe potential are a bit uncertain, so this area may shift in subsequent outlooks. ...Day 6/Sun - Ozarks to the Lower OH and TN Valleys... An upper shortwave trough will progress across the region on Sunday. Forecast guidance depicts a 50-60 kt southwesterly 700 mb jet overspreading the region during the day. Meanwhile, a surface low will intensify over MO/IL, shifting northeast along the OH River through the period. A very moist and unstable airmass is depicted ahead of the low and attendant south/southeastward-progressing cold front. Intense severe thunderstorms will likely accompany this system. Consistency among deterministic guidance, favorable synoptic pattern, as well as CSU/NSSL ML output, support introduction of 15 percent probabilities for Sunday. ...Days 7-8/Mon-Tue... Spread among forecast guidance increases substantially by the end of the forecast period. However, a pattern shift by Day 8/Tue appears possible, with an amplified upper ridge potentially building over the western half of the CONUS. Overall, predictability is too low to delineate areas of severe potential across the eastern half of the CONUS. ..Leitman.. 05/21/2024 CLICK TO GET WUUS48 PTSD48 PRODUCT