Mesoscale Precipitation Discussion 1041
NWS Weather Prediction Center College Park MD
1030 PM EST Thu Dec 06 2018

Areas affected...Coastal Southern CA

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

Valid 070330Z - 070730Z

Summary...A plume of moisture ahead of a surface low off the
southern California coast will continue to bring widespread
showers to coastal southern California. Rainfall rates as high as
0.5 to 0.75 inches per hour will be possible through late this
evening (11 PM PST) with total rainfall amounts as high as 1-1.5
inches. This rainfall over sensitive areas, including burn scars
and urban areas, could result in flash flooding.

Discussion...An analysis as of 03z showed a surface low off the
southern CA coast with an upper level low positioned off the coast
as well. This system has pumped moisture into the coast most of
today, with latest PWATs 0.9" to 1.1" per GPS data. A ribbon of
MUCAPE exists just along the coast with values as high as 500
J/kg.

Radar trends in the last hour from KNKX have shown a few clusters
of heavier rainfall pivoting into the coastline with hourly rates
as high as 1". Area mesonet observations from around the San Diego
metro area show hourly totals as high as 1" with many locations
picking up around 0.7". The hi-res models show the trends and
probabilities of exceeding 0.5"/hr rates to last through late
evening, then begin to wane with loss of instability. As the
surface low drops southeast, the onshore flow will become less
conducive for heavy rain and rainfall rates should subside.

The combination of forcing and moisture transport impinging on the
terrain areas will keep the potential for flash flooding through
late evening. 

Taylor

ATTN...WFO...SGX...

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

LAT...LON   34071696 33521637 33201635 32781633 32611649
            32561695 32551725 32951726 33301749 33381776
            33401770 33711799