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AGUS76 KRSA 111534
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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PDT Tue Mar 11 2025

...SHOWERS OVER SRN CA INTO THIS EVENING AS A LOW MOVES THROUGH...
...A LARGER COLD SYSTEM WILL BRING MORE WIDESPREAD PRECIP TO THE
REGION LATER TONIGHT INTO THURSDAY...
...ADDITIONAL SYSTEMS WILL BRING MORE PRECIP CHANCES FRIDAY INTO
THE WEEKEND...

.METEOROLOGICAL CONDITIONS (SHORT TERM: TUE AM - FRI AM)...

A closed low off the Srn CA coast with a trough deepening over the
Eastern Pacific this morning and the low gets closer to the Srn CA
coast this afternoon as the deepening trough approaches the west
coast. This will bring showers and possibly isolated thunderstorms
to Srn CA and possibly light precip to Nrn CA coast and along the
Sierra. Scattered showers wrapping around the low through Srn CA
this morning with the low offshore.  The low tapped into some
moisture with PW around 0.75 inches along the Srn CA coast. The 12Z
NKX sounding PW was 0.79 inches. Max temperatures near normal to
around 10 degrees above normal over Nrn Ca and NV and near normal to
10 degrees below normal for Central CA and below normal to around 15
degrees for Srn CA today. The low moves onshore as an open wave near
the Ca/MX border this evening and the cold front associated with the
trough/low pressure system approaches the West coast overnight.
Showers over Srn CA will taper off overnight as the shortwave shifts
east and precip increases over Srn OR and Nrn CA with southerly
winds ahead of the approaching front.  Minimum temperatures tonight
near normal to around 10 degrees above normal. Precip amounts will
be variable to showery nature.  Precip amounts generally are
forecast to be around 0.5-1.5 inches around San Gabriel Mtn and San
Bernardino Mtns and south into the San Diego County Mtns and along
the coast and generally less than a quarter of an inch elsewhere
over Srn CA and 0.5-1 inch for the Shasta Basin and 0.25-0.5 inches
for the Nrn Sierra and over the Smith Basin and along the King Range
and Srn OR Cascades, otherwise amounts generally around a tenth of
an inch or less over Nrn CA.

The cold front moves along the Pac NW and Nrn CA coast with deep
trough along the west coast Wednesday morning.  The cold front will
progress south and east through the region into Thursday morning.
The trough will move onshore late Wednesday into Thursday. This
system taps into about an inch PW plume that aims at Nrn CA coast
(PW around 0.8 inches) Wednesday morning and drops south to the
Central CA coast in the afternoon and to the Srn CA coast Wednesday
night. Showers and isolated thunderstorms are possible Wednesday
into Thursday.   Max temperatures on Wednesday generally below
normal up to 15 degrees over CA and near normal to 10 degrees below
normal for NV. Low temperatures on Wednesday night below normal up to
10 degrees over Nrn CA and near normal for Central and Srn CA and
near normal to 10 degrees above normal over NV (W-E).  High
temperatures will be chilly on Thursday will be below normal to
around 20 degrees with some record low maxs possible (especially
over Srn CA). Low temperatures Thursday night will be below normal
up to 15 degrees.  Precip amounts will be variable due to showery
nature. Moderate to heavy precip is possible near/ahead of the front
and more showery behind it. Precipitation amounts for Wednesday into
Wednesday night are expected to generally be 1-3 inches along the Nrn
and Central CA coast and Shasta Basin and along the transverse mtns
and 2-4 inches along the Sierra and 0.5-1.5 inches for the Sac
valley and 0.25-0.75 inches for the SJ Valley and up to an inch over
San Diego County mtns and half an inch or less over NV. Precip will
taper off Thursday afternoon/night as the front exits the region and
the trough shifts east. Precip amounts for Thursday into Thursday
night will generally be around half an inch or less except up to
around an inch for Srn Sierra and 1-2 inches for the San Bernardino
Mtns and south into the San Diego Cty Mtns and 0.25-1 inch along the
coast from La County to San Diego County and 0.25-0.75 inches over
Ern and Srn NV with the front moving through Thursday morning.

Freezing levels generally around 6000-8000 ft over CA and 7500-8500
ft over NV then falling to around 4000-6000 ft over Nrn CA and 6000-
7500 ft over Central CA and 6500-8000 ft over NV and rising to
around 7500-10000 ft over Srn CA tonight. Freezing levels fall on
Wednesday into Wednesday night behind the cold front with freezing
levels dropping to around 2000-5000 ft over CA and 4000-6000 ft over
NV Thursday morning. Freezing levels drop to around 1500-4000 ft
over CA and around 2500-4000 ft over NV Thursday night.


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

West to northwest flow aloft will usher in the next s/wv trof
sitting off the Pacific Northwest and northern CA coast to start the
period. However...available moisture along the immediate coast is
not overly significant with PW values generally from 0.50-inch north
to 0.75-inch south. Given these factors...as the s/wv trof dives
southeast as it moves inland...best precip amounts will be over the
far northern CA coast (mainly the Smith and lower Klamath River
basins)...and then inland over the southern Cascades down across the
northern Sierra with 0.50- to 1.00-inch (local 1.50-inches). Look
for amounts to slowly taper off for points south...becoming near or
just less than 0.10-inch across coastal southern CA. with the
trajectory from the northwest...this system will bring freezing
levels down to approx 2500- to 3500-feet north to about 3500- to
4500-feet south.

After this system continues to dig southeast over the interior...a
fairly broad upr trof will form across the intermountain west before
pushing farther downstream over the Great Plains states on Saturday.
A positively tilted upr ridge pumping up over the eastern Pacific
will then make its way along the west coast...which is now looking
to bring drier conditions to start the weekend...less precip than
the previous forecast. Then into Sunday...a s/wv trof making its way
toward the coastal waters shows a varying spread in terms of depth
and overall timing...which lowers confidence in terms of precip to
wrap up the weekend. The 11/00Z CMC is a bit more aggressive with
precip...while the GFS and to an even more extent the EC hold precip
more offshore and north. At this point...lowered confidence with
this round of precip and followed relatively close to newest 11/13Z
NBM...which spreads over northern CA (0.75- to 2.00-inches higher
terrain) and to a lesser extent central CA (0.10- to 0.50-inch
higher terrain). Freezing levels will range from 4000-feet northwest
to 7000- to 9000-feet along I-80 and 10000- to 12500-feet for
southern CA into southern NV.

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



Osborne/Kozlowski

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