Mesoscale Precipitation Discussion 0118
NWS Weather Prediction Center College Park MD
1144 PM EDT Sat Mar 30 2024

Areas affected...coastal areas of southern/southwestern California

Concerning...Heavy rainfall...Flash flooding possible

Valid 310343Z - 310943Z

Summary...A few heavier downpours along coastal areas were
producing 0.5+ inch/hr rain rates in spots near land areas.  A
conditional, yet locally significant flash flood risk will exist
with this activity for the next several hours.

Discussion...A very slow-moving mid/upper low continues across
offshore waters (centered approximately 125 mi west of Vandenburg
AFB, CA currently).  Very cold temperatures aloft has enabled
areas of 500+ J/kg MUCAPE to develop over open waters and near
immediate coastal areas per SPC mesoanalyses.  Additionally, weak
onshore wind fields (both at the surface and aloft) were promoting
upright, yet slow-moving convection to affect mainly offshore
areas.  One cell in particular, however, has made landfall near
Santa Barbara, CA over the past hour or so and produced impressive
rain rates (locally exceeding 1.5 inch/hr), potentially
contributing to a locally significant flash flood threat in that
area.

The ongoing scenario should continue for at least a few more hours
- and perhaps beyond 09Z tonight.  Mostly cellular convection will
continue to move slowly northeastward and approach coastal areas,
potentially resulting in a few spots of very heavy rain rates and
excessive runoff at times over land/coastal areas.  Instability
profiles may not support development of these cells very far
inland, although sensitive/urbanized coastal areas (and burn
scars) could experience flash flooding as weak onshore flow
maintains ~500 J/kg SBCAPE near the coast through the nighttime
hours.  Flash flood potential should stay isolated, however, and
remain dependent on cells that can make it onshore and persist for
any length of time.

Cook

ATTN...WFO...LOX...MTR...SGX...

ATTN...RFC...CNRFC...NWC...

LAT...LON   36172120 35752073 35082016 34701953 34311861
            33831785 33451736 32731702 32601718 33161803
            33761898 34061977 34472056 34912097 36112175