Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1251 AM CDT Tue May 02 2017 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST TEXAS TO SOUTHERN MISSISSIPPI... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS TO THE FLORIDA PANHANDLE... ...SUMMARY... Strong to severe thunderstorms will be possible from central/eastern Texas to the central Gulf Coast Wednesday into Wednesday night. A few of these storms will be capable of damaging winds, large hail, and a couple tornadoes. ...Synopsis... The mid/upper-level pattern will amplify through Wednesday night, as a shortwave trough advancing southeast from the northern Rockies phases with another impulse over the southern/central Plains. In turn, a larger-scale trough will deepen over the central US as it approaches the Mississippi Valley. Meanwhile, upstream ridging will build over the Inter-Mountain West. ...Central Texas eastward to the central Gulf Coast... On Wednesday morning, a warm front will likely stretch from south-central Texas eastward to the Louisiana coast and then southeast into the Gulf. Along and to the south of this boundary, rich boundary-layer moisture (characterized by surface dew points in the upper 60s/lower 70s) will be returning northward. Concurrently, a weak southern-stream impulse will advance east/northeast across southern/central Texas and the Sabine Valley, with a low-level jet developing northward along the Texas Coast. Near the exit region of this jet, convection will likely be ongoing Wednesday morning. Steep mid-level lapse rates (with related MUCAPE around 1000-2000 J/kg) and sufficient deep-layer shear will encourage a threat of large hail in stronger cells. Additionally, if sufficient moistening/warming of the boundary layer occurs, a localized tornado threat may exist in the vicinity of the warm front, as it pivots northeast through the day. A more organized severe threat will materialize across the region during the afternoon hours, as a surface low deepens across the Ark-La-Tex and a trailing cold front advances southeast. Over eastern Texas and western Louisiana, moderate/strong buoyancy and ample forcing along the front will encourage the development of a squall line that rapidly accelerates southeast through the evening. Additionally, ongoing convection over the lower Mississippi Valley (related to the southern-stream impulse) may enhance forward propagation of this line via cold-pool mergers. Damaging winds will be the primary threat, with perhaps a few instances of severe hail as well. Rich low-level moisture and favorable veering of winds with height will support some tornado threat, but it will likely be sensitive to the orientation of the squall line. Along much of the line, a general west/southwest-east/northeast orientation will result in relatively line-parallel shear vectors, unfavorable for embedded circulations. However, a few portions of the line may evolve to slightly more meridional orientation during the evening (as the mid-level trough becomes less positively tilted), supporting the potential for a few line-embedded circulations. The squall line should push southeast towards the central Gulf Coast through the evening and overnight, with the severe threat shifting towards southeastern Louisiana and southern Mississippi. ...Ark-La-Tex and vicinity... Convection will likely expand across the Ark-La-Tex during the morning and afternoon hours, initially from warm advection related to a southwesterly low-level jet across the region. Additionally, storms are expected to expand in coverage along the cold front over portions of north-central Texas by afternoon. Steep mid-level lapse rates and modest deep-layer shear may encourage a few instances of severe hail with any of these storms. Additionally, upscale growth/cell mergers could locally enhance the threat of damaging winds before the strongest convection shifts east/southeast. ..Picca.. 05/02/2017Read more
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