Graphic for MPD #0050

Mesoscale Precipitation Discussion 0050
NWS Weather Prediction Center College Park MD
105 PM EST Mon Feb 05 2024

Areas affected...Southern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 051800Z - 060500Z

Summary...Numerous to widespread flooding impacts continue across
the Transverse and Peninsular Ranges and surroundings (including
much of the LA metro) with additional localized 1-2" expected
through evening. Locally significant to extreme impacts remain
possible across the hardest hit areas.

Discussion...Moderate to heavy rainfall continues across portions
of Southern California late this morning, as a gradually weakening
atmospheric river has progressed very little over the past 12
hours. The nearly stationary plume of deep moisture is attributed
to a longwave trough and upper low along and offshore of
Northern/Central California, and a distinct dry slot is noted
between the upper low and atmospheric river. The core of the AR
(oriented directly into the LA basin) was nearly directly sampled
this morning by the NKX sounding, which measured precipitable
water values of over 1" (well above the 90th percentile and near
the max moving average, per SPC sounding climatology). MRMS
multi-sensor hourly rainfall totals have generally ranged from
0.2-0.4" over the past 6-12 hours from the Santa Monica Mountains
eastward to the San Bernardino Mountains, with 24-hour rainfall
observations generally ranging from 4-8" in the vicinity of the
Transverse Ranges (including much of the LA metro area). These
very wet antecedent conditions are resulting in the vast majority
of the additional rainfall across the Transverse Ranges
translating directly into runoff, leading to continued numerous to
widespread instances of flooding with locally significant to
extreme impacts possible (including extremely dangerous and
life-threatening flash flooding and mudslides/landslides with
potential debris flows).

Additional localized totals of 1-2" are anticipated through 05z
across upslope areas of the San Bernardino Mountains (closer to 1"
or less in the vicinity of the LA metro), and much of that will
occur over the next 3 hours or so before the plume drifts
southeast into the Peninsular Ranges (mainly affecting areas north
of San Diego). Most of these ranges have seen much less rainfall
through this event so far (with the exception of the Santa Ana
Mountains, which have picked up 3-6"), so impacts are expected to
become more isolated to scattered (and more directly limited to
the terrain) in the vicinity of San Diego. The peak of the
rainfall rates going forward are anticipated to occur in the next
3-6 hours across the southern portions of the discussion area, and
the subsequent diminishing moisture flux transport should result
in rates of generally less than a quarter inch per hour beyond 00z
(with lingering impacts from all of the runoff a distinct concern
into the late afternoon and evening hours). 

Churchill

ATTN...WFO...HNX...LOX...SGX...VEF...

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

LAT...LON   34991861 34971797 34991748 34621689 33751644
            33301661 32891679 32801686 32361723 32371859
            32922000 34312047 34662040 34841975 34961916
           
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Last Updated: 103 PM EST Mon Feb 05 2024