11PM Day 1 Convective Outlook for Monday, February 16. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE CENTRAL AND SOUTHERN CALIFORNIA COASTAL COUNTIES
SUMMARY
Strong thunderstorms may impact the coastal areas of central and southern California this afternoon and evening. These storms may produce locally damaging wind gusts, and perhaps a brief tornado.
Coastal central into southern CA
A potent upper trough will move across CA during the afternoon and evening, with a 100+ kt midlevel jet nosing across southern CA. At the surface, low pressure will deepen as it moves into central CA, with a cold front affecting much of the coastline after 18Z. Strong wind convergence along the front will result in a line of shallow convection, with embedded thunderstorms possible. This line is likely to affect the central coastline by around 18Z, and through the remainder of southern CA by 00Z. Strong wind gusts will be likely, with a few locations possibly reaching over 50 kt. Weak instability and cool surface temperatures will be mitigating factors to tornado risk, however, embedded circulations within the line cannot be ruled out.
Interior Valleys
It appears substantial precipitation will hamper heating/destabilization for much of the day, with very little SBCAPE evident on various model forecast soundings. As such, despite model low-level warm advection with veering winds with height, it appears lapses rates may not quite favor severe convection, and the low probabilities have been removed.
Coastal southwest OR and northern CA Late
Overnight, an upper trough will dive southward just off the Pacific Northwest, with the left-exit region of the upper jet pushing into northern CA early Tuesday morning. While surface temperatures will be cool and in the 40s F in the wake of the earlier wave, this secondary trough will bring cold temperatures aloft with and 500 mb temperatures to around -35 C. As such, SBCAPE of a few hundred J/kg will exist as the cold front moves across the coastal counties. Low-topped convection may produce graupel, along with locally strong wind gusts.