Graphic for MPD #0052

Mesoscale Precipitation Discussion 0052
NWS Weather Prediction Center College Park MD
1102 AM EST Tue Feb 06 2024

Areas affected...Southern California

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

Valid 061600Z - 062130Z

SUMMARY...A flash flood threat will continue for southern CA
through the early afternoon. While the coverage and magnitude of
heavy rain will be reduced compared to the previous couple of
days, sensitive grounds will maintain the risk for runoff from an
additional 1 to 2 inches of rain.

DISCUSSION...GOES West water vapor imagery showed an elongated mid
to upper level low/trough centered west of the central CA coast
with a number of smaller scale vorticity maxima embedded within
the base of the trough off of southern CA. Two of the vorticity
maxima were located ~125 miles SSW of Point Conception and along
120W at 1530Z, tracking toward the east. 12Z soundings from VBG
and NKX indicated PWATs of 0.6 to 0.9 inches, as the core of the
moisture plume has shifted east into the lower CO River Valley but
700-500 mb lapse rates of 7.4 C/km at NKX were an indicator of the
upstream environment, closer to the core of the mid-level low.
Radar and infrared imagery showers ongoing showers into Ventura
and Orange counties with moderate to heavy rain.

As the mid-level low/trough axis continues to translate
southeastward through the afternoon, 850-700 mb winds are expected
to vary in magnitude (<10 kt for the Transverse Ranges up to ~30
kt for San Diego County) but veer from their present S and SW
orientation. PWATs are expected to remain similar to their 12Z
values with only slight lowering through 21Z but the steeper
upstream lapse rates will be shifting southeastward with time and
supporting up to 250-750 J/kg MUCAPE across southern CA. Forcing
ahead of the vorticity maxima off of the southern CA coast should
continue to shift east through 21Z with an increase in showers and
shallow convective cells beneath the cold core aloft. Brief
training should support isolated 0.5 to 0.75 in/hr rates but the
majority of rain rates should remain in the 0.1 to 0.3 in/hr
range. Given the extreme rainfall observed over the past 48 hours
and areas of ongoing flooding throughout southern CA, the addition
of 1 to perhaps 2 more inches of rain will continue the threat for
flash flooding and debris flows.

Otto

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

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

LAT...LON   34361830 34291782 34231757 34171708 33931676
            33291656 32791636 32471639 32341697 32321728
            32571758 33051779 33411812 33831916 34071937
            34321904
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Last Updated: 1102 AM EST Tue Feb 06 2024