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AGUS76 KRSA 281343
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
650 AM PDT Wed May 28 2025

...SLIGHT CHANCE OF SHOWERS/T-STORMS THIS AFTN/EVE OVER THE SIERRA
AND SHASTA WITH OTHERWISE DRY CONDITIONS THROUGH THE WEEKEND...
...WELL ABOVE NORMAL TEMPERATURES FRIDAY/SATURDAY, SOME COOLING
STARTING SUNDAY...
...POSSIBLE SHOWERS INTO TUESDAY AS A LOW DROPS IN FROM THE NORTH...

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

CA sits between two upper lows this morning, one over the Pacific
southwest of soCal and a larger low traversing the Gulf of Alaska.
The gulf low also drags a large frontal system with 1" PW of
moisture across the eastern Pacific. This system will lift northward
as it approaches the west coast likely entirely missing CA in favor
of the PacNW and BC later today into tomorrow. The smaller low to
the southwest will head towards Baja arriving some time Thursday.
The combination of these systems will keep some troughing overhead
for today along with instability. This means the slight chance of
thunderstorms over parts of the Sierra and the Shasta Drainage.

In between these lows offshore, high pressure will build and shift
towards the coast the rest of the work week as the southwest low
hovers near Baja. By Friday afternoon, the ridge will be firmly
overhead with 500 mb heights exceeding 590 dm. This will keep dry
conditions over the region and bring well above normal (+10 to +20
deg F) afternoon temperatures. Overnight lows will also be well
above normal by similar amounts through Saturday. Many locations
across CA are already under heat related products (please see local
WFO pages for heat risk/alert information). Into Sunday, a trough
will move through the PacNW as the ridge shifts further inland.
Troughing will dig into nrn CA/NV as well while the low offshore of
Baja finally begins to move inland. This will provide some relief
across the region with coastal areas back to near/below normal and
afternoon temperature anomalies inland down to about +5 to +15 deg F.

Next week, models have a trough digging into the PacnW from western
Canada and closing off into an upper low before potentially heading
into CA/NV into Tuesday. There`s some disagreement between the
models and ensembles on the timing of this as well as the strength
of the system, but all four of the 500 mb height ensemble clusters
show at least some decent degree of troughing over the area by
Tuesday afternoon. A good number of the GFS/ECMWF ensemble members
even have precipitation over the Sierra, se CA, and parts of NV. The
official forecast has 0.10-0.50" over the mountains of ne NV for
Monday with showers more broadly over ne NV as well. CPC 6-10 day
outlooks predict below normal temperatures and above normal
precipitation for much of the region for early June. Given this time
of year, above normal precipitation is not a whole lot but still
worth mentioning.

Please Note: This product may NOT be routinely updated this
summer. 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



AS

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