Version:  Current  |  Back 1  |  Back 2  |  Back 3  |  Back 4  |  Back 5  |
Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
730 AM PDT Tue May 6 2025

...SHOWERS AND T-STORMS TODAY OVER SE CA & S/E NV FOLLOWED BY DRY 
CONDITIONS THE REST OF THE WEEK WITH RISING TEMPERATURES, 10 TO 20 
DEG F ABOVE NORMAL BY FRI...
...PRECIP CHANCES RETURN SUNDAY...

.METEOROLOGICAL CONDITIONS (TUE AM - MON AM)...

Troughing from the back edge of an upper low exiting into AZ 
yesterday dropped showers and thunderstorms over se CA and srn NV. 
Observations since yesterday reporting as much as 0.50-1" for some 
areas. This morning, the low continues to head east through the Four 
Corners as 0.75" to just under an inch PW lingers over srn CA. 12z 
sounding out of San Diego remains well above normal at 0.93". 
Elsewhere, another low is attempting to form off the northwestern 
edge of the main low near ID as an upper ridge builds into the 
eastern Pacific and the PacNW. Another large upper low behind the 
ridge is also making its way across the Gulf of Alaska. 

For today, a low will drop into NV from ID traveling south across 
the state into srn CA by this evening. This will generate additional 
showers and thunderstorms over se CA and e/srn NV as the low moves 
through. The low will also mitigate some warming from the offshore 
ridge allowing much of srn CA and NV to remain below normal for 
today while high pressure keeps much of nrn/cntrl CA at +5 to +10 or 
so deg F above normal. The low will exit CA on Wednesday as the 
ridge moves in behind it overhead. High pressure will strengthen 
over the region the rest of the work week keeping conditions dry and 
gradually raising temperatures. Expecting anomalies of +5 to +15 deg 
F and up to +20 deg F or so above normal by Friday continuing for 
Saturday as well.

Over the weekend, the upper low over the Gulf of Alaska will 
continue to move eastward towards BC and the PacNW. This may result 
in some showers over nrn CA on Sunday into Monday. There is some 
disagreement between the models and amongst the ensembles on the 
positioning and arrival timing of this system making for uncertainty 
in the QPF. The GFS is quicker at bringing the upper low offshore of 
the PacNW and therefore sending showers into the northern CA coast 
compared to the ECMWF (Sunday am vs Sunday pm). Ensemble spread at 
Arcata for the 24 hrs ending Monday morning is anywhere from 0" to 
an inch.

QPF is a combination of showers/thunderstorms over se/srn CA/NV 
today and showers along the north coast from a larger upper low on 
Sunday. No precip expected Wednesday through Saturday. Some 
uncertainty for the QPF in both cases due to thunderstorms today and 
model differences/ensemble spread for Sunday. Official forecast for 
Sunday was a blend of morning WPC guidance and the 13z NBM. This 
shows about 0.10" along the north coast and just under 0.25" over 
the Smith Basin with less than a tenth into Shasta. Freezing levels 
to lower into Sunday down to 7-11 kft north of Shasta in the morning 
spreading to I-80 by the late afternoon. Early Monday morning 
expecting levels 4-8.5 kft north of I-80.


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.