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AGUS76 KRSA 041554
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PST Tue Nov 4 2025

...UNSETTLED PATTERN BRINGING PERIODS OF WET WEATHER TO NORTHERN
PORTIONS OF FORECAST REGION OVER NEXT FEW DAYS...
...PRECIPITATION WILL INTENSIFY OVERNIGHT TONIGHT AND INTO TOMORROW
AS A BROADER TROF AND STRONGER ATMOSPHERIC RIVER MOVES ONSHORE...

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

Light to moderate showers continue to spread across the northern
portions of the forecast area as a frontal system and relatively
modest moisture plume continues moving onshore. Precipitation is
forecast to continue across the North Coast, Shasta Drainaige, and
S. OR throughout the day and overnight in association with this
system with 1 to 3 inches forecast over the next 18 hours. The
highest accumulations are forecast for the southern portions of Cape
Mendocino where integrated moisture transport will likley be most
favorable for orographic ascent.

Precipitation is forecast to re-intensify overnight tonight and into
Wednesday morning across the north as a broader and negatively
tilted trough swings into the region, phasing with the remnant
moisture of the current plume and intensifying atmospheric river
conditions. Precipitation is forecast to spread southward throughout
the day tomorrow with relatively high model-to-model disagreement on
exact amounts, especially across the Northern Sierra (Feather
Basin).

The heaviest precipitation accumulations (4+ inches) over the next
72 hours is focused over Cape Mendocino, the Smith Basin, and Shasta
Drainage/Trinity Alps. Strong southerly winds within the northern
Sacramento Valley may favor enahnced upslope flux over the Shasta
Drainage.

Morning forecasts generally followed guidance from the NBM and WPC.
The EC and GFS show large disagreement in total accumulations with
the EC higher across the North Coast and the GFS higher (nearly
double the EC) along the Norhtern Sierra. NBM guidance falls more in
line with the wetter scenario in both locations. Forecasts will
continue to adjust as guidance updates.

Additional atmospheric river activity is forecast to bring lighter
precipitation to locations across the north with relatively modest
precipitation accumulations and shower activity throughout the rest
of the week beginning on Thursday. Most of this shower activity is
confined to the North Coast though a few hundredths to a couple
tenths could spread as far south as Sonoma County along the Coast
and Donner Pass along the Sierra on Friday into Saturday morning.

Freezing levels will remain between 9k and 12k feet across the north
today before lowering to 7k and 10k feet by Thursday morning under
the digging trough.

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.

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



CH

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