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AGUS76 KRSA 061428
HMDRSA

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.

QPF graphics are available at www.cnrfc.noaa.gov/qpf.php



AS

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