SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0240 PM CDT Mon May 03 2021 Valid 032000Z - 041200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST TX AND SOUTHEAST OK INTO THE MID-MS VALLEY... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHEAST... ...SUMMARY... The greatest severe-thunderstorm threat appears to be from late afternoon through tonight in a corridor from northeast Texas and southeast Oklahoma to the Lower Ohio Valley. Very large hail, tornadoes (a couple of which may be significant), and intense damaging winds are expected. ...20z Update... Only minor adjustments have been made to the convective outlook with the 20z update. The main change is to trim the Marginal and Slight risk areas across parts of IA/MO based on the current location of the surface cold front and ongoing/developing convection. Other minor adjustments have been made to the Slight risk area across parts of upstate SC into central NC based on current observations and radar trends. Otherwise, the forecast philosophy remains unchanged from the previous outlook. See below for the previous discussion, and reference MCDs 494, 495, 496, and 497 for near-term details/expectations. ..Leitman.. 05/03/2021 .PREV DISCUSSION... /ISSUED 1123 AM CDT Mon May 03 2021/ ...Southern Great Plains to Mid-South... Two primary corridors of severe thunderstorms are expected to develop by late afternoon. The first within a post-frontal regime off the higher terrain of NM spreading east across the TX South Plains towards the Big Country and western north TX. Very steep mid-level lapse rates in conjunction with robust speed shear in the mid-upper portion of the thermodynamic profile should prove favorable for a long-track supercell or two with a primary hazard of large to significant severe hail. The second area of severe thunderstorms will rapidly develop along the dryline to surface front intersection across central TX before spreading into southeast OK. Large buoyancy given the very steep mid-level lapse rates will support intense supercells capable of all hazards, some of which will be significant. Guidance still differs on the degree of low-level flow response this evening rendering uncertainty over how long discrete supercells will be maintained. Given rich boundary-layer moisture coupled with the large MLCAPE, there is concern for at least conditional significant tornado potential across a portion of north TX into southeast OK. If upscale growth occurs too quickly, this may not be realized, but have highlighted a corridor of enhanced tornado potential in this region. Otherwise, upscale growth will occur at some point this evening rendering a predominant severe wind threat spreading east-northeast towards the Mid-South through tonight. ...Southeast... Scattered thunderstorms will persist across a broad swath of the southeast states through this evening. A shortwave trough over the OH Valley will move east with the belt of stronger low/mid-level flow to its southeast focused across the Carolinas and VA. Along the periphery of moderate buoyancy, the threat for a few tornadoes and scattered damaging winds should develop from GA to southeast VA. Farther west, low-level flow will become increasingly veered and slowly subside through the afternoon. However, larger buoyancy along the eastern periphery of the EML emanating east from the south-central states will maintain a threat for scattered damaging winds and large hail. ...Midwest... An MCV over northeast MO will be the primary mechanism for scattered thunderstorm development across the Mid-MS Valley into IL late today. Abundant cloud coverage downstream should delay the severe storm threat until at least late afternoon. An additional swath of severe storm development is anticipated along the cold front in MO where more robust boundary-layer heating is underway. This activity will likely grow upscale into an east-southeast moving MCS towards the Lower OH Valley region this evening with damaging winds becoming the primary hazard.
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