SPC Dec 6, 2023 Day 4-8 Severe Weather Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CST Wed Dec 06 2023 Valid 091200Z - 141200Z ...DISCUSSION... ...East TX to the Lower OH Valley and Deep South... A moderately unstable air mass should become established during the day on D4/Sat from southeast TX to the Ark-La-Tex and Ark-La-Miss ahead of a cold front pushing southeastward. With increasing mid-level height falls across the warm sector downstream of a highly amplified/positive-tilt upper trough over the central states, thunderstorm development will become widespread both along and ahead of the front by afternoon. Stronger low-level flow will be coincident with correspondingly weaker instability in the northeast portion of the warm sector. Low-level southwesterlies will be more moderate and subsiding with southwest extent where instability should be larger. As such, below-average confidence exists regarding the distribution of severe hazards, but signal remains sufficient to maintain a highlighted 15 percent area embedded within a broad low severe probability. Primary change with this outlook is to expand the areal delineation farther northeast in the Mid-South. ...Southeast to Mid-Atlantic States... Guidance has trended towards increased agreement with a highly amplified upper trough centered across much of the MS Valley at 12Z Sun to rapidly progress towards the Northeast and Mid-Atlantic during the D5 period. This will result in a deepening surface cyclone tracking roughly from the OH Valley to the St. Lawrence Valley. This type of evolution should result in very strong to extreme southerly low-level winds largely paralleling the meridional orientation of the surface cold front sweeping east. Unlike on D4 where the 00Z deterministic ECMWF and its ensemble probabilities had less instability forecast with northern extent than the 00Z deterministic GFS and its GEFS probabilities, the opposite is progged for D5. Still, a thermodynamically limited warm sector is likely given weak mid-level lapse rates and meager buoyancy at most. But with conditional potential for this to overlap the strengthening low-level southerlies, low severe probabilities remain apparent over at least the central/eastern Carolinas to the Delmarva. Read more