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CNRFC Hydrometeorological Discussion

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PST Thu Feb 6 2025

...A SYSTEM MOVES THROUGH TODAY INTO FRIDAY BRINGING 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 MORE WIDESPREAD PRECIP 
POSSIBLE MID-WEEK NEXT WEEK...

.METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - SUN AM)...

An upper level low/shortwave trough positively tilted off the Pac NW 
coast and a sfc low approaching the Central CA coast this morning 
and sfc low moves onshore this afternoon/evening and the upper level 
shortwave trough moving through the region tonight into Friday. PW 
plume about 1.05 inches aimed at the Central CA coast this morning 
spreads from the Bay area around Point Conception to around LA 
County and inland in the afternoon then focused on the Srn CA coast 
tonight into Friday morning and dropping south into Mexico in the 
afternoon.  This will bring precipitation to Srn OR and most of CA 
(except SE) and much of NV today and tonight with showers tapering 
off during the day of Friday as the shortwave trough moves off to 
the east.  Precip has started over the Bay area and Central CA coast 
and spreading inland into the Nrn Sierra this morning. Slight chance 
of thunderstorms over Nrn CA and along the Sierra today. The 
forecast is generally a blend of NBM and WPC with some of the latest 
forecast and in some locations mixed with the HRRR resulting in a 
generally increase in amounts for today into tonight especially 
along the Central CA coast and the sierra and over the transverse 
mtns compared to yesterday afternoons forecast. Precipitation totals 
for today into tonight generally around 1.5-3.5 inches for the 
Sierra and Central CA coast and 1-2.5 inches for the transverse mtns 
and 0.5-2 inches along Nrn Ca coast and Shasta Basin and 0.5-1.5 
inches for the Sac Valley and generally a half an inch or less over 
Nevada and SJ valley. Precipitation amounts for Friday generally 
nothing up to a half an inch except locally up to an inch possible 
over the San Gabriel and San Bernardino Mtns and in the Srn Sierra 
on Friday. Freezing levels around 3000-4000 ft near the ORCA border 
to around 4500-6500 ft for the Nrn and Central Sierra and Nrn NV and 
6500-8500 ft for Srn Sierra and 7000-10000 ft over Srn NV this 
morning then around 2500-3500 ft near the ORCA border and 6000-
7500ft over the Nrn and Central Sierra and 7500-8500ft for the Srn 
Sierra and 7000-9500 ft over NV and 8000-12000 ft over Srn CA this 
afternoon. Freezing levels drop Friday morning 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.  

Another weak shortwave trough moves into the Pac NW and brushes Nrn 
CA on Saturday. Not much moisture with this system with PW less than 
half an inch. A chance of light precipitation to NW CA and the Srn 
OR Cascades on Saturday with amounts generally a tenth of an inch or 
less on Saturday. Freezing levels around 2000-3000 ft near the ORCA 
border on Saturday.  


.METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)...

A weak disturbance will be exiting the area from southern CA toward 
AZ to start the weekend with a west-to-east aligned s/wv trof 
dropping south from western Canada toward the Pacific Northwest on 
the downstream side of a narrow wavelength upr ridge situated along 
140W. Model spread is a bit tighter this morning as compared to 
yesterday with the general pattern of dropping the s/wv trof across 
the region on Sunday into Monday. The GFS has trended closer to what 
the EC and CMC was previously showing...which has increased 
confidence in widespread light to locally moderate precip. Best 
totals look to fall along the length of the Sierra and the coastal 
mountains of southern CA from Point Conception to the CA/MX border 
(0.50- to 1.00-inch). Also...given the trajectory of this 
system...this will usher in a cooler airmass across the region. 
Freezing levels early Saturday will start from near 2500-feet north 
and east to 9000- to 10000-feet south and west. By Monday...as the 
cold air settles in across the area...freezing levels will bottom 
out from near sea-level north to 4000-feet far south.