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CNRFC Hydrometeorological Discussion

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PDT Fri May 29 2020

...SYSTEM TO BRING COOLING AND NORTHERN CA PRECIP SATURDAY...
...UNSETTLED PATTERN THROUGH NEXT WEEK WITH CONTINUED COOL AND 
CHANCES FOR PRECIP...

.METEOROLOGICAL CONDITIONS (FRI AM - THU AM)...

Satellite imagery this morning shows the upper ridge shifting 
eastward, with an upper low off the SoCal coast centered near 
33N/125W. Mid and Upper level clouds are starting to stream into CA 
from the south ahead of the low's progression, fed by a weak 
moisture plume. Some isolated showers and tstms may develop over 
higher terrain of the Sierra this afternoon and evening as a result. 

The brunt of the system is expected to arrive early Saturday 
morning, as the low makes quick northward progress today. Expect 
precip to spread into northern CA coastal areas during the early 
morning hours, then further into the North Coast, Shasta, and 
Northern Sierra by late morning. Heaviest periods continue to be 
focused between 12Z-00Z Saturday, from Cape Mendocino northward, and 
over the Shasta basin. Expect precip to wrap up overnight into 
Sunday as the low lifts into the Pac NW. Freezing levels should be 
around 8000-ft or above. 

An upper trough develops on Sunday, and dominates the pattern for 
the early half of next week. On Monday, expect a s/wv to pass 
through far northern areas, scattering showers near the OR/CA border 
and Nrn CA plateau, mainly during the evening hours. For Tues/Wed, 
an upper low develops, pinched off the upper trough, and the GFS 
rotates a series of s/wv's through the region as offshoots of that 
parent low. This would bring periods of showers and tstms to the 
Sierra crest and higher terrain of Northern CA and NV Tuesday, 
Wednesday, and potentially Thursday. In contrast, the EC has the low 
parked further to the west and south than the GFS indicates, which 
keeps the region dry. The current forecast reflects the possibility 
of precip during this period as the NBM and WPC trended, but there 
is still high uncertainty.