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SPC Mar 28, 2024 Day 4-8 Severe Weather Outlook

1 year 6 months ago

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0400 AM CDT Thu Mar 28 2024 Valid 311200Z - 051200Z ...DISCUSSION... ...Day 4/Sunday: Mid Mississippi Valley into the Central/Southern Plains... The upper trough/low over the western states should slowly advance eastward towards the Southwest and southern/central High Plains on Sunday. Upper ridging is forecast to remain over the central/ southern Plains through Sunday night, which in tandem with a low-level temperature inversion should tend to suppress most convection. One possible exception may be along a sharpening warm front across MO/IL, where some guidance suggests elevated convection may form either Sunday morning, and/or Sunday night with strong low-level warm advection/lift occurring. Steepening mid-level lapse rates are forecast to overspread the mid MS Valley from the southwest through the period. These lapse rates, along with increasing moisture/instability in the presence of strong deep-layer shear, may support a risk for isolated supercells with associated threat for large hail. Regardless, confidence remains too low in this mainly elevated convection occurring, given upper ridging persisting, to add a 15% severe area for Sunday along/near the warm front in MO/IL at this time. ...Day 5/Monday: Southern/Central Plains into the Mid Mississippi and Ohio Valleys... Even though some differences remain in medium-range guidance regarding the ejection of an upper trough over the central CONUS on Monday, confidence has increased in the general location of relevant surface features, including the primary low, position of a southward-extending dryline, and northward extent of the warm front into the OH Valley. Even though the overall upper trough orientation may remain somewhat positively tilted, most deterministic guidance shows that a mid-level speed max and associated shortwave trough will eject northeastward over the southern/central Plains through Monday evening. Low-level mass response should encourage the eastward development of a surface low to the OK/KS vicinity in a similar time frame. Favorable low-level trajectories emanating from the Gulf will act to increase low-level moisture in tandem with steepening mid-level lapse rates and daytime heating across a broad warm sector extending from the southern/central Plains into the lower/mid MS Valley and OH Valley. A favorable thermodynamic and kinematic environment for organized severe convection will exist across much of these regions, with supercells capable of producing large hail and tornadoes possible initially. With time Monday evening/night, some upscale growth seems probable across the mid MS and OH Valleys, as mid-level flow should become increasingly parallel to a surface cold front. Therefore, a 15% severe area has been introduced for Monday where confidence is greatest that robust convection will develop in a parameter space characterized by weak/moderate instability and strong deep-layer shear. A nocturnal minimum in severe convective potential may be realized Monday night into early Tuesday morning across parts of the lower MS Valley into Mid-South, given the positively tilted nature of the upper trough. ...Day 6/Tuesday: Ohio/Tennessee Valleys into the Appalachians... Some severe threat should continue Tuesday over parts of the OH/TN Valleys into the Appalachians as the upper trough continues eastward. Even though there is still some uncertainty with the exact placement of the primary surface low and evolution of the upper trough, enough confidence exists in a fairly narrow corridor across these regions to add a 15% severe area for Tuesday. Rich low-level moisture should be in place ahead of an eastward-moving cold front. Redevelopment and/or re-intensification of convection seems probable by Tuesday afternoon. Strong deep-layer shear and weak instability should be sufficient for organized severe convection posing some threat for damaging winds, and perhaps tornadoes given the forecast strength of a low-level jet focused over parts of the OH/TN Valleys. The northward extent of the severe risk across OH and vicinity remains uncertain, as the placement of the warm front varies in model guidance. Similarly, convection should eventually encounter a less unstable airmass across the Appalachians. But, an isolated severe risk may continue Tuesday evening into early Wednesday morning across the southern/central Appalachians into portions of the Southeast. ...Day 7/Wednesday and Day 8/Thursday... Predictability remains too low to include a 15% severe delineation for Wednesday across the Mid-Atlantic/Southeast along/ahead of a cold front. By this extended time frame, there are significant differences in model guidance regarding the evolution of the upper trough, including its possible interaction/merging with a northern-stream trough, and placement of relevant surface features. Still, at least an isolated severe risk may persist Wednesday along/ahead of the eastward-sweeping cold front. Once this front clears the East Coast, severe potential appears minimal across the CONUS next Thursday. Read more