SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0652 AM CST Tue Jan 26 2021 Valid 261300Z - 271200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF SOUTHERN ALABAMA...THE FLORIDA PANHANDLE...CENTRAL/SOUTHERN GEORGIA...AND A BIT OF ADJACENT SOUTH CAROLINA... ...SUMMARY... A few strong to marginally severe thunderstorm gusts are possible today through tonight over parts of the Southeast, and a tornado cannot be ruled out. ...Synopsis... Mid/upper-level split flow will continue over western/central North America, now directed largely by a strong trough and embedded/ compact cyclone centered over the Grand Canyon area. The 500-mb low will move/redevelop eastward across the southern Rockies to southeastern CO by 00Z, with trough across southern NM to western Chihuahua. By 12Z, the trough (which may still contain a modest closed low over KS) will extend across southwestern IA, eastern KS, south-central OK and central TX. Downstream, a weakening trough was apparent in moisture-channel imagery over IA to the KS/MO border area. This perturbation should accelerate eastward across the Northeast through the end of the period, while continuing to deamplify. At the surface, the 11Z analysis showed a decelerating cold front arching across eastern TN, central AL, southeastern MS, and southeastern LA, becoming quasistationary from there southwestward across the TC shelf waters of the northwestern Gulf. The rest of the frontal zone should become quasistationary today -- under nearly parallel flow aloft -- from the Carolinas across GA and southern AL to southeastern LA. A frontal-wave low is expected to develop tonight over LA and ripple along the front toward southwestern AL by about 12Z tomorrow. ...Southeast... Isolated to scattered thunderstorms are possible in multiple episodes throughout the period, beginning with a band of convection now along the northern rim of the outlook area of GA/AL. The main concern will be isolated damaging gusts, though a tornado could occur with some mesoscale to storm-scale augmentation of an only weakly supportive ambient environment. Direct upper support will be lacking, with the weakening northern trough and stronger/progressive southwestern low/trough each far-removed from this area. However, two indirectly related factors will help to maintain a conditional and marginal severe threat: 1. A tight height gradient of southwesterly to west-southwesterly flow will persist, and 2. An increase in the LLJ is progged late in the period (after about 06Z) in the early-stage mass-response/warm-advection field preceding the approaching southwestern system. A favorably rich and deep layer of low-level moisture will remain in place along and south of the front, with surface dew points generally in the mid 60s F to isolated low 70s. This will offset modest low/middle-level lapse rates to yield fairly persistent MLCAPE in the 500-1200 J/kg range away from active convection. Somewhat veered surface flow will limit convergence and vertical shear (especially low-level shear). However, speed shear will remain favorable (contributing to 45-55-kt effective-shear magnitudes), given the gradient flow aloft, and some hodograph enlargement is possible under the LLJ late. ..Edwards/Gleason.. 01/26/2021
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