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AGUS76 KRSA 121448
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PDT Wed Mar 12 2025

...COOL SYSTEM WILL BRING PRECIP AND COOLER TEMPERATURES INTO
THURSDAY ACROSS THE REGION...
...ADDITIONAL SYSTEMS WILL BRING MORE PERIODS OF PRECIP FRIDAY INTO
MONDAY ESPECIALLY OVER THE NORTH...


.METEOROLOGICAL CONDITIONS (SHORT TERM: WED AM - SAT AM)...

A trough off the west coast with an associated cold front along the
Pac NW and Nrn CA coast this morning. Scattered showers over Srn OR
and Nrn CA this morning ahead of the front. This system taps into
about an inch PW plume that aims at Nrn CA coast (PW around 0.8
inches) this morning (12Z Oakland sounding PW 0.83 inches and 09Z
sounding at Marysville from CW3E has Integrated Water Vapor of 0.81
inches). The Pw plume drops south to the Central CA coast in the
afternoon and to the Srn CA coast Wednesday night. The cold front
will progress south and east through the region into Thursday
morning bringing periods of moderate to heavy precip near and ahead
of the front and more showery precip behind the front. The trough
will move onshore late Wednesday into Thursday bringing more
scattered showers. Isolated thunderstorms are possible today into
Thursday. Max temperatures today will be generally below normal up
to 15 degrees over CA and near normal to 10 degrees below normal for
NV. Low temperatures tonight will be near normal to 10 degrees below
normal over CA and near normal to 10 degrees above normal over NV (W-
E). High temperatures will be chilly on Thursday with temperatures
below normal up 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. Precipitation amounts into tonight
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.

The trough moves east out of the region Thursday night as a
shortwave trough approaches the Pac NW/Nrn CA coast. The shortwave
trough and associated front move SE through the region on Friday
into Friday night bringing more showers to the region, especially
over the north. Max temperatures Friday will be below normal to
around 20 degrees. Friday night lows will be near normal to around
10 degrees below normal. PW plume about an inch off the Central CA
coast and around Point Conception Friday morning shifts south off
the Srn CA coast in the afternoon.  Precip amounts for Friday into
Friday night are generally forecast to be 0.5-1.5 inches along the
NW Ca coast and into the Shasta Basin and along the Srn OR Cascades
and around 0.5-1 inch along the Nrn Sierra and Eel Basin and up to
half an inch for the Sac Valley and 0.25-0.75 inches for the Russian
Basin and Central CA coast and into Santa Barbara/Ventura County and
the Central and Srn Sierra and generally less than a quarter of an
inch for the rest of Srn CA and over Nrn and Central NV (except a
couple hundredths to none over SE CA and Srn NV).

Freezing levels generally around 4000-6000 ft over Nrn CA and 6000-
7500 ft over Central CA and 6500-7500 ft over NV and around 7000-
10000 ft over Srn CA this morning. Snow level radar at Happy Camp is
around 4700 ft this morning.  Freezing levels will fall during the
day today into tonight 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. Freezing levels
rise to around 3000-4000ft over Nrn CA and 4000-6000 ft for Central
CA and 6000-8000 ft over Srn CA and 3500-5500 ft over NV on Friday
night.


.METEOROLOGICAL CONDITIONS (LONG TERM: SAT AM - TUE AM)...

An upr ridge will be nudging toward the west coast...aligned
generally along 135W to start the period....while at the same
time...the s/wv trof moving southeast across the area on Friday will
be exiting the Great Basin toward the Desert Southwest...leaving
northwest flow aloft across the region. With the next area of
moisture advecting northeast from west of Hawaii reaching an area
near the CA/OR border and WAA/isentropic lift increasing on
Saturday...look for continued light precip under the dirty ridge for
portions of northern CA. Freezing levels will rebound with the
warmer airmass moving in and reaching 5000- to 7500-feet for the
northern third of the area...8000- to 10000-feet for the central
section...and from 10500- to 12500-feet for the southern third.

Then for the latter half of the weekend a s/wv trof will move out of
the northeast Pacific toward the west coast. Still enough variation
amongst the 12/00Z models to lower confidence in this feature...but
as was the case yesterday...the GFS and CMC are consolidating on one
scenario of being a bit more shallow and faster...while the EC has
kept with its elongating of the feature and being slow with its
approach toward the region. Latest WPC QPF and 12/13Z NBM follows a
bit closer to the shallow/faster solution...which will bring the
best precip to the higher terrain of northern CA with anywhere from
1.00- to 3.00-inches or so...slightly higher across the Smith River
basin. Lower elevations will generally be in the range of 0.25- to
0.75-inch. Amounts will then taper off across central CA with the
highest totals for this portion of the state over the southern
Sierra (0.75- to 1.50-inches)...and next over the Santa Cruz
Mountains and Big Sur coast (0.25- to 0.75-inch). Lower elevations
will remain from 0.10- to 0.33-inch. Freezing levels will drop with
the passage of the s/wv trof...down to about 2500- to 4500-feet for
areas near and north of I-80...and then for central CA into southern
NV from 4000- to 6500-feet...and for southern CA 7500- to 9000-feet.


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



Osborne/Kozlowski

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