Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Dec 19 2023 08:19:24

FOUS30 KWBC 190819
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
318 AM EST Tue Dec 19 2023

Day 1
Valid 12Z Tue Dec 19 2023 - 12Z Wed Dec 20 2023

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS COASTAL
CALIFORNIA...

A strong, anomalously deep closed upper low currently well
offshore the Pacific Northwest will drop southeastward toward the
central California coast by early Wednesday morning. This system
will bring an unsettled and active weather pattern to much of the
coastal areas of California through the rest of this week,
beginning today/tonight across mainly northern/central California
coast where the greatest forcing for ascent exists. A plume of
higher moisture, characterized by PWs near/exceeding 1" and IVT
values 400-500 kg/m/s (per CW3E), will brush the coastal areas and
lead to a threat of hourly totals in excess of 0.5". The 00Z HREF
neighborhood probabilities for 0.5"+ in 1-hr peak near 70 percent
along the coast north of the Bay Area, which may lead to some
isolated flooding, particularly for sensitive and urban areas.
24-hr totals approaching 2-2.5" are expected with isolated higher
amounts near 3" possible along the coast. Across the northern
Sierra, snow levels will be relatively high, so the expected 2-3"
totals may lead to some flooding concerns.

Taylor


Day 2
Valid 12Z Tue Dec 19 2023 - 12Z Wed Dec 20 2023

....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
CENTRAL AND SOUTHERN CALIFORNIA...

The strong closed mid/upper level low will slide southeastward
just offshore the California coast through Wednesday and Wednesday
night. The position of the upper low will put the coastal areas in
the favored area of upper diffluence with a steady plume of
moisture nosing into the region from the southwest. Per the CW3E
page, the latest IVT forecasts reach near 500 kg/m/s, directed
somewhat orthogonal to the terrain areas of the central California
coast. Moisture anomalies reach near the 90th percentile. In
addition to the higher moisture, some instability is expected to
develop given the steepening lapse rates shown in the forecast
soundings. The latest model guidance shows a broad area of 2-4"
24-hr totals across the central/southern California coastal areas,
particularly for the Transverse Ranges where the orientation of
the IVT plume is most perpendicular and hourly totals may reach
0.75-1" at times. This rainfall and expected rain rates may lead
to scattered instances of flash flooding, some of which may be
locally significant for the Transverse Range areas given some of
the higher sensitivities and terrain effects.

Taylor

Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!7FN16UGW0eY-njaRTPYCsB3tS0xM3KfJpKzcegVttTNZ=
DidXy04zZ1V-6ocbQ1i1ppmLqLFeoD1XmbHLYEa6j5mM4YY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!7FN16UGW0eY-njaRTPYCsB3tS0xM3KfJpKzcegVttTNZ=
DidXy04zZ1V-6ocbQ1i1ppmLqLFeoD1XmbHLYEa6WNCAN9E$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!7FN16UGW0eY-njaRTPYCsB3tS0xM3KfJpKzcegVttTNZ=
DidXy04zZ1V-6ocbQ1i1ppmLqLFeoD1XmbHLYEa6icD_46k$=20


$$



=3D =3D =3D
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