SPC AC 311956 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Wed Oct 31 2018 Valid 312000Z - 011200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST TEXAS TO SOUTHWEST MISSISSIPPI... ...SUMMARY... The greatest risk for severe thunderstorms, capable of producing damaging winds, hail, and tornadoes, exists from southeast Texas to the lower Mississippi Valley through tonight. ...Discussion... Have removed severe probabilities from portions of the Big Country into north Texas, where the south/southeastward progression of a cold front and an expansive trailing precipitation shield are likely minimizing any severe threat. Additionally, Marginal probabilities have been extended westward towards El Paso, where forcing for ascent with the primary shortwave impulse may continue to support a localized hail/wind threat. Otherwise, a greater tornado/damaging wind potential is still expected to materialize late this evening into tonight from southeast Texas to the lower Mississippi Valley, and no changes have been made to the ongoing probabilities here. For more information on this threat, see the previous discussion below. ..Picca.. 10/31/2018 .PREV DISCUSSION... /ISSUED 1129 AM CDT Wed Oct 31 2018/ ...TX today to LA/MS overnight... A midlevel shortwave trough now near El Paso will continue eastward across TX through tonight. Weak cyclogenesis is expected by this evening and continuing through tonight, along a pre-existing front from central TX to the Mid South. A moist low-level air mass is already present south of the front, with low 70s boundary-layer dewpoints spreading across the northwest Gulf coast. Gradual mass response to the cyclogenesis will result in strengthening low-level flow/shear, especially tonight across LA/MS. Ongoing convection in TX has largely remained elevated atop the frontal surface, but may gradually transition to surface-based storms along the front later this afternoon. Isolated strong-severe storms will also be possible this afternoon/evening into southwest TX, along the west edge of the richer low-level moisture and in the zone of stronger low-midlevel ascent preceding the shortwave trough. Farther east, the ongoing warm sector convection across the upper TX coast should persist through the afternoon and spread slowly eastward/northeastward. Additional warm sector storm development is also expected tonight along the moist axis into southern LA. Wind profiles are only marginally favorable for organized/supercell storms at present across TX, with slow strengthening of vertical shear expected later this afternoon through tonight farther east toward the lower MS Valley. A few supercells could evolve from the ongoing upper TX coast convection, as well as embedded supercells/bowing segments along the front from central into east TX. This frontal convection will likely evolve into a line that will move eastward overnight, with an accompanying threat for damaging winds and a couple of tornadoes with embedded circulations. The more substantial supercell/tornado threat is expected overnight into parts of LA (and possibly MS) within the moist sector, and where low-level shear becomes the strongest. A strong tornado or two will be possible, especially with any pre-frontal supercell clusters, where effective SRH increases to greater than 400 m2/s2 in a moist environment with sufficient surface-based buoyancy.
Tornado Outlook
Strong Wind Outlook
Hail Outlook
Severe Thunderstorm Outlook
