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AGUS76 KRSA 222126
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
125 PM PST Fri Nov 22 2024

...FOCUS OF HEAVY PRECIP OVER I-80 CORRIDOR THIS AFTERNOON/EVENING...
...COLD FRONT CONTINUES PRESSING ACROSS CENTRAL CA TOMORROW...
...NEXT ROUND OF PRECIP MONDAY INTO TUESDAY...

.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI PM - MON AM)...

The cold front is making its way across northern CA this
afternoon...finally. Radar imagery and automated gauge data
indicates the best amounts falling from the Feather River basin
over the Sierra back to the southwest across the Sacramento area and
then down I-80 to the SF Bay area. Several gauges in this swath of
precip have easily surpassed 0.75-inch with localized amounts to
1.00-inch within the first 3 hours since 22/18Z. Behind the main
frontal band...precip has tapered off considerably across the north
cost down through the upper portions of the Russian River basin and
then inland over the Shasta Lake drainage and northern Sacramento
Valley.

Through this evening...precip will be slow to sag south of the I-80
corridor...waiting on an offshore s/wv trof and associated upr jet
streak to reach the coast...which will nudge the boundary and
moisture plume south toward central CA. For the 00-06Z
period...moderate to heavy precip will fall from the Feather through
the American River basins in the Sierra...and then back through the
Sacramento area and much of the SF Bay Area south of the Golden
Gate. These areas...which have been void of much precip so
far...will see a 6 to 12 hour period of rather heavy precip with
anywhere from 1.00- to 3.00-inches. Then overnight and into
tomorrow...the frontal boundary and associated moisture plume will
move south across the central part of the state before reaching
southern CA and dissipating.

Freezing levels are still elevated ahead of the cold
front...generally 8000- to 10000-feet along I-80. Behind the frontal
boundary...freezing levels are already dropping in the range of 4500-
to 5500-feet. This cooler air will filter in across northern CA
tomorrow with 3500- to 5500-feet over northern and central CA along
with northern NV...and higher from 6000- to 11500-feet across
southern CA and southern NV.


.METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)...

Expect an upper low off the Pac NW coast with a moisture plume off
the central CA coast at the beginning of the period.  As moisture
transport increases on Mon, expect precip rates to increase central
CA.  An uptick in precip rates is expected in far NW CA as well
closer to mid-level forcing combined with onshore (but not as moist
as further south) flow.  Model spread is fairly high in terms of
placement and intensity of precipitation associated with this
system.  Some ensemble members show some heavy amounts still, and a
couple show heavy precip lingering in nearly the same location in
the southern Sierra for an extended period of time.  Models show the
plume exiting the region by midweek for the most part, with lots of
spread in this time frame too.  Followed NBM through Mon evening to
try to match the latest guidance, especially with WPC being wetter
on the north coast.  Followed WPC beyond Mon evening.  Overall
changes were slightly drier in the northern Sierra by generally 0.3"
or less and wetter on the central coast and San Joaquin Valley (up
to 0.2") and southern Sierra (0.6-1.0").  Freezing levels are
forecast to range from 4000-6000 ft in far northern CA/NV, 6000-9000
ft central (area of highest precip amounts), and over 10,000 ft
further south.  Little change in freezing level was noted.


QPF graphics are available at www.cnrfc.noaa.gov/qpf.php



Kozlowski/Lerman

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