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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
700 AM PDT Fri Apr 25 2025

...PRECIP CHANCES INCREASE WITH UPR LOW TODAY THROUGH SUNDAY...
...LIGHT PRECIP POSSIBLE FAR NORTH/EAST WITH WEAK SYSTEM TUE-WED...

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

The elongated and negatively tilted upr trof along and just off the 
west coast is beginning to form a cutoff low west of Cape Mendocino 
along 130W this morning...while at the base of this feature a vort 
max is rotating north-northeast from near Point Conception and will 
reach NV late this afternoon and evening. Radar imagery already 
shows scattered returns moving northward across the region with the 
best concentration in the vicinity of the CA/NV border near Mammoth 
Lakes and points northward.

Through today...look for the upr low to drop to the southeast and 
reach just west of the central CA coast by this time tomorrow. 
Scattered showers will be most numerous in an area of deformation 
across southern OR...and an area of diffluence aloft across portions 
of central CA. For Saturday...this will be the best day for precip 
production as the upr low slow moves east across central CA toward 
southern NV. The best precip totals will fall from northeast CA 
southward along much of the Sierra and along coastal areas between 
Big Sur and Los Angeles. With precip being scattered...overall 
amounts could vary where heaviest cells track...but areal averages 
will be in the range of 0.25- to 0.75-inch in these locations. 
Elsewhere...scattered precip will be possible. SPC is also showing 
the potential for t-storms in their Day 1 and Day 2 outlooks over 
portions of northern/central CA into much of NV except the far 
southern and eastern locations. This is when the coolest air moves 
overhead with freezing levels dipping to 4500- to 7000-feet...all 
depending on proximity to the upr low.

Sunday sees the upr low track toward northeast NV before exiting 
east of the area late in the period...leaving an elongated upr trof 
back to the southwest with northerly flow aloft developing across 
much of the region. Best precip will be in the vicinity of the upr 
low...across the Humboldt River basin...with amounts ranging from 
0.25- to 0.75-inch (heaviest across the Ruby Mountains). Scattered 
showers may be possible all the way back to the Sierra. 

Into next week...a weak will tack across northern/eastern areas on 
Tuesday into Wednesday...which may generate some scattered precip.