12AM Day 2 Convective Outlook for Saturday, January 3. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN THE SOUTHEAST AND PARTS OF CA/OR
SUMMARY
Isolated severe storms are possible across parts of the Southeast on Saturday, and the Sacramento/northern San Joaquin Valleys to coastal northern California-southwest Oregon in the afternoon/early evening.
Southeast
A positive-tilt shortwave trough will progress east across the Lower MS Valley to off the South Atlantic Coast by Saturday evening. An attendant weak surface cyclone should track from central AL to offshore of SC by 00Z, with a cold front trailing west-southwest to the central Gulf Coast. Low-level warm conveyor convection should increase during the mid to late morning, with a separate round of thunderstorms developing near the surface low to along the front by midday into the afternoon. Low-level hodograph curvature will be modestly enlarged within the warm conveyor as it shifts east through the day, but surface-based instability should remain weak with low-probability tornado/wind threats.
It appears probable that a corridor of moderate buoyancy with MLCAPE of 1000-1500 J/kg should extend from around the mouth of the MS River towards the western FL Panhandle by midday. However, low-level flow will be increasingly veered in this portion of the warm sector ahead of the front. Sufficient deep-layer speed shear should exist for a few supercells with mid-level rotation, which may produce isolated severe hail and eventually isolated damaging winds as storms cluster during the afternoon.
Central Valley to coastal northern CA/southwest OR
Most guidance depicts multiple shortwave impulses ejecting northeastward from a deep upper trough off the Pacific Coast. The southern impulse should move across central CA during the afternoon, while a more vigorous northern impulse impinges on coastal OR during the afternoon to early evening.
The southern shortwave will be favorably timed for diurnal convective development across the Sacramento and northern San Joaquin Valleys. Meager buoyancy should develop amid an elongated hodograph. This should be sufficient for transient rotating cells, which could pose a low-probability threat of a brief tornado. Sub-severe hail and locally gusty winds may also occur.
The northern shortwave will be accompanied by a renewed strengthening of low-level flow, likely reaching 50-65 kts along the northern CA/southwest OR coast. Buoyancy will remain scant, but cold mid-level temperatures aloft should support low-topped convection that could contribute to localized severe gusts. Transient rotating cells may also develop offshore and approach the northern CA coast with a waterspout/low-probability brief tornado risk.