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Hydrometeorological Discussion
National Weather Service / California-Nevada RFC / Sacramento CA
800 AM PST Wed Nov 11 2026

...DRY CONDITIONS THROUGH THURSDAY EVENING AS THE REGION SITS UNDER 
HIGH PRESSURE...
...CHANCES FOR HEAVIER MORE WIDESPREAD PRECIP FRIDAY THROUGH EARLY 
NEXT WEEK AS A PAIR OF SYSTEMS MOVE THROUGH...

.METEOROLOGICAL CONDITIONS (WED AM - TUE AM)...

Dry conditions through most of tomorrow as an upper ridge sits 
across CA/NV and the Four Corners. A trough offshore of CA will push 
the ridge further inland tomorrow as it moves southeastward towards 
southern CA. This will clear the way for a larger upper low to 
approach from the Gulf of Alaska. The low/trough offshore of soCal 
may bring some showers to coastal soCal Thursday night and Friday 
morning ahead of the main system. The main low will send a cold 
front with about 1" or so PW of moisture wrapped around it towards 
the PacNW and northern CA. Initial showers expected to arrive along 
the north coast overnight Thursday before pushing onshore early 
Friday. The GFS is still a bit behind the ECMWF but that gap has 
narrowed since yesterday. Moderate showers moving onshore by mid 
morning heading into the Bay Area and the northern Sierra by the 
afternoon. 

With the HREF officially enjoying retirement, taking a look at the 
REFS exceedance probabilities show strong chances (40-80%) of rain 
rates of at least 0.50"/hr along the nrn CA coast tomorrow as that 
front heads inland and a 15% chance of embedded 1"/hr rates. Expect 
chances of thunderstorms as well behind the front. Troughing from 
the parent upper low will keep showers going over nrn CA after the 
front has passed with heavier precip focusing over the 
central/southern Sierra Friday evening as showers head into southern 
CA. Troughing will push inland across CA Friday night before moving 
through NV Saturday morning. Precip will diminish behind the system, 
but lingering scattered showers are expected as the next upper low 
quickly approaches. QPF totals for this first system remain 
uncertain due to ensemble spread which is about 2" along the north 
coast/northern Sierra and 1" along the central coast. QPF clusters 
show disagreement on how far heavier precip will spread along the CA 
coast stopping it around Point Reyes or spreading it all the way to 
the western Transverse. Disagreements on those exact amounts as 
well. There is good agreement, however, on the highest totals 
overall across the north coast, Shasta, and the Sierra.

Some brief ridging separates the two systems expected to impact the 
region this week the rest of Saturday. Then, the next approaching 
upper low will send another moisture wrapped cold front into the 
west coast. Previous model runs of the ECMWF had the front arriving 
and moving through Sunday while the GFS had the timing closer to 
Monday. The GFS has since sped up its timing in better agreement 
with the det ECMWF, though still lagging by a few hours at least. 
The timing spread within the ensemble members has also narrowed. 
All have the front bringing precip into nw CA before late Sunday 
afternoon. The front and precip should then move through central CA 
Monday as troughing descends into the area. At this point, there is 
some disagreement on the depth of the trough with the GFS predicting 
a deeper system and again lagging it behind the ECMWF timing wise. 
At the end of the forecast window the ECMWF has the axis of a 
shallower trough just entering NV while the GFS has the deeper 
trough axis still right along the CA coast. The difference is the 
GFS having another 0.10-0.75" of precip over central/southern CA 
overnight Monday compared to less than 0.10" from the ECMWF.

The official forecast started with either WPC guidance or the latest 
NBM and then blended in some of the west WRF over the terrain areas. 
Trimmed back the precip again on Sunday to match the timing closer 
to the ECMWF/GFS as the NBM looked a bit over spread in comparison, 
fairly similar to yesterday in that regard. Highest totals over the 
next six days over the nrn CA coast, Shasta, and across the Sierra. 
Again, expect amounts to change as we get closer to the weekend. QPF 
through 12z Tues: 2.25-4.50" Sonoma County northward along the coast 
(4-5.25" Smith Basin), 3-7.50" Shasta, 1.50-5" Sierra, 1-2" Bay 
Area, 0.50-1.50" central coast (up to 2.50" Santa Cruz mountains and 
Big Sur coast), 0.25-1.50" down the valleys (up to 2.30" closer to 
the foothills), and 0.50-1" coastal soCal.


Please Note: This product may NOT be routinely updated.
Please refer to the following product issued by the CNRFC
www.cnrfc.noaa.gov/Daily-Briefing for a graphical summary of
weather and hydrologic conditions.