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AGUS76 KRSA 052115
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
130 PM PST Wed Feb 5 2025

...LINGERING SHOWERS MAINLY OVER NW CA COAST INTO SHASTA BASIN AND
OVER PORTIONS OF SRN CA AND SRN SIERRA TODAY...

...ANOTHER SYSTEM MOVES THROUGH THURSDAY INTO FRIDAY BRINGING MORE
PRECIP TO MOST OF THE REGION....

...MAINLY DRY OVER THE WEEKEND INTO MONDAY EXCEPT LIGHT PRECIP
POSSIBLE OVER NW CA AND SRN OR CASCADES THEN A SYSTEM BRINGING MORE
PRECIP MID-WEEK NEXT WEEK...

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



An upper low off the Pac NW coast and and another low around 140W
33N and a nearly stationary front draped around Santa Barbara and
into Central NV this afternoon. PW around 0.8 inches off Srn CA
coast today. Scattered showers continue over the NW CA coast and
into the Srn Cascades and Shasta Basin and along Srn CA coast (Santa
Barbara Cty dry behind the front) and into the mountains this
afternoon.  Little change in the forecast into tonight with increase
around a tenth of an inch for the Smith Basin and a few hundredths or
less Srn CA coast into mtns.

The srn sfc low moves to the CA coast and inland on Thursday as the
northern low digs behind it with the shortwave trough moving through
the region Thursday night into Friday. This will bring more
widespread precipitation to most of the region Thursday into Friday.
PW plume around 1.05 inches aimed at the Central CA coast Thursday
morning and drops south around Point Conception in the afternoon and
along the Srn Ca coast Thursday night into Friday morning then south
into Mexico in the afternoon.  Increased amount thursday into Friday
especially along the Central CA coast and Srn Sierra and transverse
mtns (about a quarter of an inch to over an inch).  The heaviest
amounts Thursday into Thursday night are expected along the coast
from Cape Mendocino to around Point Conception  and along the Sierra
with generally 1-3 inches and 0.5-1.5 inches for the transverse mtns
and over the Shasta Basin  and 0.3-1 inch along coast in Ventura and
LA counties and less than a quarter of an inch Orange county and
south. Precip amounts for Friday (mainly during the day) generally a
tenth of an inch or less except 0.1-0.6 over the Sierra and over Srn
CA coast and into the mtns. Precip will taper off Friday
afternoon/night as the shortwave moves east through the region.

Freezing levels generally around 2000-5000 ft (N-S) over Nrn CA and
around 6000-9000 ft along Srn Sierra and NV and 8000-12,000 ft over
Srn CA will generally rise (with warm air advection) to around 2500-
4000 ft near the ORCA border to around 5000-7000 ft for the Nrn and
Central Sierra and Nrn NV and 7000-9000 ft for Srn Sierra and Srn NV
Tuesday afternoon then drop Friday morning (behind the system) to
around 2000-4000 ft over Nrn CA and around 4000-7000 ft over Srn
Sierra and around 7000-12000 ft over Srn CA and around 5000-9000ft
(NW-SE) over NV.

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

Continued confidence in a dry/cold period through the weekend once
the system moves into the Intermountain West late Friday. No change
to the afternoon forecast of minimal shower activity associated with
the departing system early Saturday and and the potential change to
another wet pattern Tuesday.

The long term window will remain generally dry and cold as the
forecast area remains situated under the upstream portions of a
broad upper-level trough. Shortwave activity on Saturday increases
the potential for very light precipitation over the North-Coast on
Saturday, though chances are low. Daily high temperatures are
forecast to remain 5 to 15 degrees below normal throughout the long
term window.

Guidance has trended towards a shift back to wet weather mid-next
week with a few scenarios beginning to spread precipitation across
northern California early Tuesday morning. Uncertainty on exact
timing of this regime shift is still very high and will be adjusted
with new guidance.

Freezing levels are forecast to remain around 2.5-5k feet across the
north and 6-11k feet across the south. A slight lowering to 9k feet
across the south through the weekend.


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



Osborne/CWH

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