Administrators NorthGeorgiaWX Posted March 8 Administrators Posted March 8 SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0655 AM CST Fri Mar 08 2024 Valid 081300Z - 091200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TEXAS TO SOUTHERN ALABAMA... ...SUMMARY... A tornado threat exists today into tonight from parts of Louisiana to southern/eastern Alabama. Large hail or strong-severe gusts are possible over the same areas and westward into parts of north and east Texas and southeastern Oklahoma. ...Synopsis... Broadly cyclonic flow, astride increasingly phased northern- and southern-stream troughing -- will shift eastward across the central CONUS through day-1. Through this period, the southern-stream component -- with a series of vorticity maxima initially extending from the Desert Southwest to the southern Plains -- will remain more influential. The associated trough should reach central KS, the TX South Plains, and northern Chihuahua by 00Z. By 12Z, the northern part of the trough will reach the Ozarks and begin phasing with a northern-stream shortwave trough digging southeastward across the upper Mississippi Valley. The southern trough will extend from the Ozarks southwestward over central/southwest TX to the Big Bend region. Several meso-alpha- and smaller-scale vorticity lobes (some convectively generated/augmented) should traverse the foregoing southwesterly flow aloft. At the surface, 11Z analysis showed weak lows near ACT and ABI, which should consolidate toward the eastern low in the next few hours. A cold front extended south-southwestward to just downstream from DRT on the Rio Grande. A diffuse warm-frontal zone was drawn east-southeastward across east TX, central/southeastern LA, and the Gulf offshore from AL and the FL Panhandle. The cold front should reach to near a JAN-GLS-MFE line by 00Z, then from central AL southwestward across southeastern LA to the northwestern Gulf by 12Z tomorrow. The warm front will remain diffuse while shifting northeastward over southern parts of MS/AL and the western FL Panhandle, ahead of a convective plume discussed below. ...TX/OK to Gulf Coast States... Multiple episodes of thunderstorms are expected across the outlook corridor today, with the greatest potential for well-organized, surface-based convection from parts of east TX eastward to near the GA/AL line, in and near the "slight risk" area. Severe gusts, isolated large hail and a few tornadoes are all possible. Potential appears to be tied primarily to three regimes, with isolated warm-sector supercell(s) possible south and southeast of them: 1. An initially elevated corridor of precip and embedded thunderstorms -- now apparent in composited radar imagery over portions of western/central MS and northern LA. This activity should persist and expand lengthwise somewhat as the foregoing airmass destabilizes today -- with sustained low-level warm advection in its inflow layer lowering the elevation of effective- inflow parcels to surface-based with time over the Gulf Coastal Plain. Modest lapse rates aloft will be offset to some extent by increasing low-level theta-e with time and with southwestward extent, as mid/upper 60s F surface dewpoints spread east- northeastward through the day to meet the convective plume. Diabatic heating will be steady and modest, owing to persistent cloud cover, but MLCINH should decrease with time across much of the area south of about I-20. Favorable deep shear is expected (effective-shear magnitudes around 45-60 kt) along with variably large hodographs and 150-300 J/kg SRH in the lowest km. This will yield a favorable supercell/tornado environment, but dominant messy/training convective modes may limit overall organization of severe potential somewhat. 2. Thunderstorms initially in a band from north-central to south- central/southwest TX, near the I-35 corridor and the low/cold front, may increase severe potential as they shift eastward into the western fringes of the environment discussed above, through the remainder of the morning. Some of this activity may merge with the southwestern part of the initially separate first regime to create a very long swath of strong-severe thunderstorms by mid/late afternoon from southern AL to southeast TX. The combined swath of convection should shift slowly eastward/southeastward over the remainder of the outlook area into tonight, maintaining potential for damaging gusts and a few embedded tornadic mesocirculations. 3. An afternoon area of thunderstorms rooted in or just above the boundary layer poleward of the low and frontal zone, across parts of OK and north TX, and spreading southeastward with mainly large-hail/ isolated-gust potential before weakening this evening. Despite the cool surface conditions, some convection may be rooted at or near the surface, with cold midlevel temperatures nearest the trough aloft contributing to steep low/middle-level lapse rates and MUCAPE potentially reaching the 1000-1500 J/kg range. Strong mid/upper flow will contribute to effective-shear magnitudes of 40-50 kt, supporting organized convective potential. ..Edwards/Jewell.. 03/08/2024 Read more View the full article Quote
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