SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0640 AM CST Tue Mar 02 2021 Valid 021300Z - 031200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are possible today through tonight across parts of the central/northeastern Gulf Coastal Plain eastward to coastal Georgia, southern South Carolina and northern Florida. ...Synopsis... A split-flow pattern in mid/upper levels exists over the central CONUS, related to a strong shortwave trough, and accompanying compact cyclone centered over eastern OK. The cyclone should open up at 500 mb, but remain a strong shortwave trough, while moving eastward across the Mid-South and Delta regions around 00Z, then to portions of GA/western SC by 12Z. Another, greater split-flow regime is evident offshore from CA, with a large synoptic cyclone centered near 35N131W in latest moisture-channel imagery. Potential convective influences from that feature along the southern CA Coast should be delayed until the day-2 period. At the surface, 11Z analysis showed a wavy, quasistationary frontal zone across central FL and the north-central Gulf, to a low roughly south of LCH and east of CRP. The front is expected to drift northward across central/northern FL through 00Z while the low migrates to shelf waters south of the western FL Panhandle. Between 00-12Z, the Gulf low will move east-northeastward across the AAF area and weaken, engaging in an effective cross-peninsular "handoff" process as a new low forms over the Atlantic near the GA shoreline or extreme northeastern FL East Coast during the last few hours of the period. ...Northern/northwestern FL late overnight... Scattered thunderstorms are forecast to move across the southern GA/eastern FL Panhandle/northern FL area tonight, in a regime of low-level warm advection and strengthening flow ahead of the mid/upper trough. Activity over GA should be rooted atop a stable layer north of the front. Deep/speed shear will become favorable (45-55-kt effective-shear magnitudes) across the region, ahead of the mid/upper trough. Some of the more aggressively destabilizing forecast soundings from deterministic progs suggest that the air mass along and south of the front, over northern FL, may support a severe threat late tonight. Sufficient low-level destabilization to yield nearly surface-based inflow parcels is possible after 06Z, along parts of the FL coastal bend and perhaps inland across the CTY/GNV/JAX vicinity. Near-surface flow should veer across northern FL during the weakening of the Gulf low and formation of the Atlantic cyclone. Because of the antecedent, relatively small/stable boundary-layer theta-e values inland, that veering is needed to advect better- modified Gulf air inland over this region -- but also, would reduce low-level hodograph size, shear vectors, storm-relative surface flow, and convergence. Most (but not all) in the SREF, MREF and GEFS suites also appear weak on instability/lift, with modest lapse rates both in and above the boundary layer. Given these counterbalancing influences, especially involving uncertainty of enough inland destabilization and warm-sector lift, the severe potential still appears too conditional/isolated to introduce an outlook area at this time. However, prognostic and mesoscale trends will be monitored through the period for stronger and more- consistent evidence. ..Edwards/Jewell.. 03/02/2021
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