Graphic for MPD #0051
Mesoscale Precipitation Discussion 0051
NWS Weather Prediction Center College Park MD
1130 PM EST Mon Feb 05 2024

Areas affected...Southern California...

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

Valid 060430Z - 061500Z

SUMMARY...Warm conveyor belt finally pushes through San Diego
county and the Peninsular Ranges with occasionally moderate
rainfall rates up to .33"/hr & additional 1-1.5" totals
maintaining any ongoing flooding.   Additional, scattered to
widely scattered narrow core convection may occur with rates up to
.5" and totals of .75-1.25" across saturated areas may result in
localized possible flash flooding through early morning.

DISCUSSION...CIRA LPW denotes the core of the remaining AR/Warm
conveyor belt along the cold front is currently directed at
eastern Orange county into San Diego county and points south into
Baja California.  A narrow ribbon of 1" total PWATs (generally
below 500mb) continues to be advected by southwesterly 25-40kts of
LLJ from 850-700mb, though that axis is obliquely oriented to the
Peninsular range, the depth of moisture and winds still supports
400-500 kg/ms of IVT this will support a few hours remaining of
.25-.33"/hr rates across the Peninsular Range with additional
totals reaching 1" and maybe near 1.25" at best oriented peaks
within the range.  While this area has not seen the dramatic
rainfall totals, prior bout earlier this week still depicts a
fairly well saturated upper soil ratio (55-70%) which keeps the
0-40cm layer in the 75th to 85th percentile, suggesting above
normal run-off is probable, with rapid onset/flash flooding
condition possible along some already above normal creeks/streams.

Further West...
GOES-W WV suite depicts the remaining upper-level closed low has
opened into a more SSW to NNE oriented trough axis from NW CA to
just northeast of the 30N130W benchmark.  This trof continues to
advance eastward providing modest height-falls but more
importantly, increasing cold air aloft.  This supports steepening
lapse rates.  While the low levels have been scoured a bit,
sufficient lingering moisture and some localized higher
temperatures in the mid to upper 50s through the Channel Islands
and coastal regions of Santa Barbara toward Ventura county are
starting to see an uptick in instability for some widely scattered
to scattered convective cold air showers to develop within the
weak DPVA and divergent flow along the left exit of the 150kt jet
core nosing into northern Baja California.  Given the favorable
large scale ascent, a few of areas of remaining moisture and low
level convergence within the California Bight may enhanced for
shallow convective cores capable of modest but sufficient moisture
flux to support up to .75"/hr rain rates.  Low level flow has
weakened and so, steering flow for the shallow cells may be a bit
more chaotic and slow moving especially along the Santa Barbara to
Los Angeles County coastal area including some convergence near
some of the Channel Islands, so duration is likely to be less than
an hour, but some may linger enough for localized totals of
.75-1.25" through early morning.  Given the area has hydrophobic
soil or still ongoing flooding...even these narrow core convective
cells will have the potential to induce localized flash flooding.

While there is already ongoing/remaining flooding across the Los
Angeles Basin, the Flash Flooding tag for this MPD is considered
Possible for potential for new incidents through 15z on Tuesday
morning, both with the AR/Warm Conveyor Belt as well as the
shallow scattered convective cores nearer the approaching
mid-level trough axis. 

Gallina

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

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

LAT...LON   35022040 34721991 34551914 34331832 34251747
            34001702 33471658 32681650 32511716 32761783
            32741853 32961908 33291966 33992046 34602074
            34902070
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Last Updated: 1130 PM EST Mon Feb 05 2024