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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
1240 PM PST Mon Nov 17 2025

...WIDESPREAD PRECIP AND POSSIBLE T-STORMS THE REST OF TODAY ACROSS 
CA AS AN UPPER LOW MOVES THROUGH...
...LINGERING SHOWERS AND T-STORMS OVER SRN CA TUES, THEN A SECOND 
UPPER LOW TO RETURN PRECIP CHANCES TO THE REGION MID TO LATE WEEK...

.METEOROLOGICAL CONDITIONS (MON PM - SUN AM)...

A low continues to travel along the coast rotating precipitation 
into CA this afternoon. Lightning detection is picking up some 
flashes in the SJ Valley as radar shows scattered areas of 
precipitation across much of the state. Heaviest areas right now are 
focused over coastal srn CA, specifically Santa Barbara/Ventura 
counties right around the cold front and a narrow plume 1"+ PW of 
moisture. HREF exceedance probabilities show a 40-75% chance of 
0.50+"/hr rain rates over that area the rest of the afternoon and 
isolated areas across the state at a 10-30% chance. Rain rates 
should then begin to diminish later this afternoon into this 
evening. Models have the low continuing to move south along the 
coast the rest of today and tomorrow resulting in additional 
scattered showers and thunderstorms before moving inland around srn 
CA/Baja on Wednesday. Relatively minimal changes in QPF from this 
morning around 0.10-0.50" up or down from 18z today to 00z Thurs for 
the current system. Expecting another 0.50-1.50" or so for coastal 
srn CA, 0.75-2" for the southern Sierra, 0.25-0.75" for the central 
coast mountains, and generally 0.10-0.50" elsewhere. Locally higher 
under thunderstorms. It is also possible that precip will exceed the 
forecast again over the western Transverse.

For the rest of the forecast period, another upper low is still set 
to approach from the nw on Wednesday traveling south offshore of 
the CA coast the rest of the week then heading inland late this 
weekend through srn CA/Baja. The same points of disagreement remain 
on timing and the trajectory of the system, but the models have come 
a little closer together in the 12z runs. Still a good deal of 
uncertainty due to that disagreement and ensemble spread. 48 hr QPF 
clusters ending Saturday morning show anywhere from less than 0.25" 
to 2" over coastal srn CA and over 5" across the Transverse on the 
higher end. Ensemble members from each det parent are pretty well 
spread out across the 4 clusters so this is more than just basic det 
model disagreement. The amount of precip will largely depend on how 
close the low is to the coast as it moves south and when it decides 
to take a turn and head inland. Bottom line, a wet pattern looks to 
continue for the rest of the week and into the weekend. Changes from 
this morning's forecast include an increase of 0.10-0.50" or so 
along the srn CA coast and generally 0.10-0.25" changes elsewhere 
along the coast. QPF 00z Thurs to 12z Sun: 0.75-1.50" coastal srn 
CA, 0.25-0.75" rest of the CA coast, and 0.10-0.50" for most of the 
rest of CA.