SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1222 PM CDT Mon May 03 2021 Valid 041200Z - 051200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR SOUTHEAST ARKANSAS...LOUISIANA...MISSISSIPPI...TENNESSEE...ALABAMA AND NORTHWEST GEORGIA... ...SUMMARY... Widespread strong to severe thunderstorm development is possible Tuesday from the lower Mississippi and Ohio Valleys into the Allegheny and Cumberland Plateau regions. This will include a risk for large hail, damaging wind gusts and a few tornadoes. ...Synopsis... The severe weather forecast for Tuesday remains complex with lingering uncertainty. Most of the forecast changes for this cycle are peripheral/modest for the Slight and Enhanced risk areas. The Marginal risk area has been expanded quite a bit to the east, from the South Carolina to Delmarva coast. On a broader scale, an upper trough extending from the Upper Midwest to southwest TX/northeast Mexico will migrate eastward, becoming oriented from the upper Great Lakes to GA by Wednesday morning. Several smaller shortwave perturbations are forecast to eject northeastward across parts of the lower MS Valley to the lower Great Lakes vicinity as well as portions of the central Appalachians/Mid-Atlantic vicinity. At the surface, a seasonally moist airmass will be in place, with mid 60s to low 70s dewpoints as far north as the TN Valley and into the Carolinas/Chesapeake Bay vicinity. Low to mid 60s dewpoints will spread further north into the lower Great Lakes eastward toward the I-95 corridor from Philadelphia into southern NJ. Meanwhile, an EML characterized by steep 700-500 mb lapse rates around 7-8 C/km will advect eastward across the lower MS Valley into the TN Valley, aiding in strong destabilization with MLCAPE values forecast around 2000-3000 J/kg. Weaker, but still sufficient lapse rates will exist across parts of the Ohio Valley eastward to the mid-Atlantic coast. A belt of increasing southwesterly midlevel flow will overspread much of the lower MS Valley into the Mid-Atlantic ahead of the main upper trough, providing further support for organized convection. As a result, a broad area of strong to severe thunderstorms are expected across a large part of the southeastern US into the Mid-Atlantic. ...Lower MS Valley/Southeast... The greatest/most concentrated severe threat on Tuesday appears to extend parts of AR/LA eastward into TN/AL/GA. Some uncertainty continues across this region as ongoing convection is expected over parts of the area during the morning hours as an MCS spreads eastward across the Ohio Valley and perhaps parts of the TN Valley. How this system from the Day 1/Monday period evolves will have some impact on how further convection develops later in the morning/afternoon as the airmass recovers ahead of the main surface cold front spreading southeast through the afternoon. Little capping is expected across the area and pockets of stronger heating will likely result in early development of thunderstorm clusters across parts of MS/AL/GA. While effective shear will initially be modest, this should rapidly increase through the morning. This initial activity will pose a threat for all severe hazards, including hail, damaging gusts and a couple of tornadoes. By late morning/early afternoon, convection is expected to develop along the surface cold front from parts of AR into far east TX. Some of this activity will likely remain cellular initially amid supercell wind profiles. With midlevel lapse rates around 7.5-8 C/km this activity could produce significant hail, in addition to damaging gusts and a couple of tornadoes. With time, stronger forcing and boundary-parallel deep layer flow should result in upscale growth into bowing/linear segments as convection shifts eastward across MS/LA and into AL during the afternoon/evening. This will increase the potential for more widespread damaging gusts, and favorable low level speed shear should continue to support mesovortex tornado potential along the line. ...Ohio Valley to the Mid-Atlantic... A moist boundary layer (low to mid 60s F dewpoints) beneath modest midlevel lapse rates will be in place on Tuesday amid 35-50 kt 850-700 mb west/southeasterly flow. MLCAPE values around 1500-2500 J/kg are forecast as pockets of strong heating result in steepening low level lapse rates. Low level flow will remain weak, but marginal supercell wind profiles should support isolated to scattered organized thunderstorm development during the afternoon. A well-mixed boundary layer, with inverted-v low level thermodynamic profiles indicate potential for locally damaging gusts. Some of the stronger cells also could produce marginally sever hail. Some guidance suggests that the morning MCS over parts of OH/TN Valley may continue eastward and spread into parts of VA/NC/SC. If an organized convective system can be maintained, this could increase damaging wind potential during the afternoon/evening and an upgrade to Slight risk could be needed in later outlooks. ..Leitman.. 05/03/2021
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