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SPC Feb 12, 2025 2000 UTC Day 1 Convective Outlook

5 months 2 weeks ago

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0155 PM CST Wed Feb 12 2025 Valid 122000Z - 131200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF LOUISIANA MISSISSIPPI AND ALABAMA... ...SUMMARY... Severe thunderstorms are expected to continue this afternoon through late tonight from the Lower Mississippi Valley into western GA. The main potential is for damaging winds and tornadoes, a few of which could be strong (EF2+). ...20z Update... The prior forecast remain valid with only minor changes to the thunder area over parts of east TX and parts of AR. Multiple bands of convection along the surging cold front over the Sabine Valley should continue to steadily intensify as broad height falls from the advancing trough overspread the western edge of the warm sector characterized by surface dewpoints in the upper 60s to low 70s F. These storms should eventually coalesce into a broader QLCS as the front accelerates. 50-60 kt of deep-layer shear will support organization into bowing segments and embedded supercell structures. Damaging winds and a couple tornadoes appear likely. Farther east over southern LA, MS and AL, strong low-level warm advection is occurring in the vicinity of an east-west oriented warm front and weak frontal cyclone rapidly lifting north over the southern Gulf Coast. As ascent intensifies with the approach of the upper trough, strong observed pressure falls of 2-3 mb per hour will rapidly advect pristine upper 60s to low 70s F surface dewpoints (evident on the 18z LIX sounding) northward. Several bands of convection (including a few supercells) have developed and should continue to intensify through the afternoon. The rapid air mass modification/destabilization will overlap with substantial vertical shear, supporting supercells capable of all hazards, including a strong tornado. The severe threat will likely persist through the evening and overnight hours as the emerging QLCS shifts eastward in the narrowing warm sector over eastern AL and western GA. Despite waning buoyancy, continued advection of near 60 F surface dewpoints and very strong low-level shear (ESRH 300-400 m2/s2) will support the risk for a few tornadoes and damaging wind gusts where the line can stay near-surface based overnight. See the prior outlook for additional information. ..Lyons.. 02/12/2025 .PREV DISCUSSION... /ISSUED 1044 AM CST Wed Feb 12 2025/ ...Lower Mississippi Valley to Southeast States... As a longwave trough amplifies over the Great Plains, strengthening cyclonically influenced deep-layer southwesterly winds will partially overlie an increasingly moist/unstable northward-shifting warm sector today, with storms expected to steadily increase in coverage and intensity through the afternoon especially across parts of Louisiana/Mississippi into Alabama. Early morning analysis features a northward-shifting maritime warm front just inland from, and parallel to, the Gulf coast, with near-70F surface dewpoints becoming increasingly common as of 9am CST/15z from the upper Texas Coast to near the New Orleans Metro and Alabama/Florida border vicinity. Similarly, even prior to the warm front arrival, the KLIX 12z observed sounding sampled a 1.63 inch Precipitable Water and 13.3 g/kg mean mixing ratio, which are in the upper 5-10 percent of daily climo values, illustrating the quality of near-coastal low-level moisture. While multi-layer cloud cover is prevalent north of the warm front, more aggressive heating/isolation is evident in proximity to the Gulf coast with deepening cumuliform development within the warm sector. These trends in concert with short-term guidance suggest that MLCAPE will exceed 1000 J/kg especially across southeast Louisiana, the southern half of Mississippi into southwest Alabama by mid/late afternoon. Expect warm sector storm development to begin during the early afternoon once convective inhibition erodes. Given the strength of deep-layer shear and expected low-level curvature, some supercells capable of all severe hazards, including tornadoes, are possible. A few strong tornadoes are possible. In particular, short-term guidance advertises a notable increase in southwesterly 850 winds (lowest 1-2km AGL) by early evening (circa 00z) across Mississippi/Alabama, which could enhance potential for supercell sustenance and stronger tornado potential late this afternoon through evening. Another round of thunderstorms is anticipated during the evening and overnight as the cold front accelerates east-southeastward across the region. The strength of these storms could be modulated by the coverage of the preceding afternoon storms, with greater storm coverage reducing buoyancy. However, current expectation is that persistent low-level theta-e advection will allow for airmass recovery, and that strong to severe storms are likely within this convective line. Primary severe risk with the line is damaging gusts, but low-level shear will remain strong enough to also support the potential for QLCS-related tornadoes as well. Read more