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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
130 PM PDT Wed Apr 8 2026

...A PAIR OF UPPER LOWS WILL BRING WIDESPREAD PRECIP TO THE REGION 
LATER TODAY THROUGH THE WEEKEND...
...T-STORMS POSSIBLE OVER NRN/CNTRL CA/NV IN THE AFT/EVE THE NEXT 
FEW DAYS...

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

Overall, forecast remains on track for a pair of upper lows to bring 
widespread precip and cooler temperatures to the region later today 
through the weekend. Det models have come a little closer together 
on the 500 mb height pattern differences on Sunday, but disagreement 
remains. Ensemble spreads have not changed much from this morning 
either. 24 hr QPF at Blue Canyon in the northern Sierra shows 
spreads roughly between 0.50" to 2.50" for Saturday and Sunday with 
spreads at Arcata 0.50" to 1.50". Variations on the exact 
positioning of the system, even slight ones, make a difference as 
precip is expected to be terrain driven. Focus is still across the 
Sierra and the higher terrain areas of nrn CA. Where the higher 
amounts will focus remains a source of uncertainty in spite of the 
12z det models getting a little closer together than this morning. 
Where this particularly helps is with regard to freezing levels. The 
positioning of the low on Sunday were different enough to result in 
nearly 1000 ft of differences in freezing level forecasts over parts 
of the Sierra between the GFS and the ECMWF. That difference is now 
more on the order of 500 ft or so. How much precip will spill over 
into the valleys is also uncertain, often with these offshore 
systems models may initially over predict that spillover and then 
dial in and reduce QPF over the valleys as we get closer to arrival 
time. Thunderstorms remain possible as well, over nrn CA today and 
nrn/cntrl CA/NV tomorrow/Friday.

The afternoon update was mainly a blend of WPC guidance and the 
latest NBM that just came in. This continues to shift precip a bit 
northward with increase of 0.25-1" north of the Monterey Bay and 
decreases of 0.10-0.50" to the south. Total QPF for the next 6 days: 
2-5.75" Sierra, 2-5.50" Shasta, 1.50-3.75" nrn CA coast, 0.50-1.50" 
greater Bay Area (over 2" possible Santa Cruz mountains), 0.25-0.75" 
coastal srn CA (up to or just over 1" Transverse), and 0.30-1.75" 
down the valleys.