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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.