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AGUS76 KRSA 071515
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PDT Mon Apr 7 2025

...SHOWERS MAINLY AROUND I-80 AND NORTH TODAY AND OVER THE SMITH
BASIN AND W SLOPE OF THE SRN OR CASCADES ON TUESDAY THEN DRY AND
WARMER WEDNESDAY INTO THURSDAY AFTERNOON...
...CHANCE OF SHOWERS OVER THE FAR NORTH LATE THURSDAY INTO
SATURDAY...

.METEOROLOGICAL CONDITIONS (SHORT TERM: MON AM - THU AM)...

A shortwave trough and associated front moved through the Pac NW/
Nrn CA overnight into this morning bringing showers down to around
the I-80 corridor this morning.  Another disturbance moves into the
Pac NW this afternoon bringing additional showers mainly along the
coast and over the higher terrain. 12Z Oakland sounding PW 1.15 i
inches this morning with a PW plume around an inch aimed around the
Bay area.  The PW plume erodes and retreats as it moves south off
the Central CA coast this afternoon.  Showers taper off overnight
tonight. Forecast precip amounts into tonight are around 0.25-0.75
inches for the Smith Basin and Shasta Basins and over the Srn OR
Cascades and the Nrn Sierra and elsewhere generally a quarter of an
inch or less and a  tenth of an inch to nothing over the Sac Valley
and far Nrn NV. Yet another shortwave moves through farther to the
north into B.C./Pac NW on Tuesday. Showers mainly confined to the
Smith Basin and Srn OR Cascades and possibly the Shasta Basin on
Tuesday with amount generally a quarter of an inch or less. Showers
diminish Tuesday night as ridge builds into the region. Ridging over
the region on Wednesday for warmer and dry conditions in between
systems.

Maximum temperatures generally below normal up to 15 degrees over
Srn OR and Nrn CA and near normal to around 12 degrees above normal
elsewhere this afternoon and near normal to around 10 degrees below
normal over Srn OR and Nrn CA and near normal up to 15 degrees above
normal elsewhere Tuesday afternoon. Max temperatures warm to around
5 to 20 degrees above normal (except near normal along the Nrn CA
coast) on Wednesday.  Low temperatures generally near normal to
around 10 degrees above normal for most of CA and around 5 to 15
degrees above normal for SE CA and NV Tuesday morning and Wednesday
morning and warm to around 5 to 20 degrees above normal Thursday
morning.

Freezing levels around 5000-9000 ft over Nrn CA and fluctuate around
9000-12,500 over Central and Srn CA and 8000-11,500 ft over NV this
morning. Freezing levels around 4000-9000 ft over Nrn CA and 9000-
12,000 ft over Central CA and 12,000-13,000 ft over Srn CA and
around 7000-12,500 ft over NV (N-S) Tuesday morning then rising to
around 9000-14,000ft over the region (N-S) Wednesday morning.

.METEOROLOGICAL CONDITIONS (LONG TERM: THU AM - SUN AM)...

An upper ridge will remain over the region Thursday as a trough
approaches the PacNW. This will keep conditions dry across the
majority of the region alongside well above normal temperatures with
anomalies of +10 to +20 deg F. The southern edge of the trough/front
to the north may bring a few showers to far nw CA around the Smith
Basin late Thursday afternoon/evening. Another shortwave will rotate
around into the PacNW on Friday potentially generating a few
additional showers along the north coast, srn OR Cascades, and
across the CA/OR border. The trough will also begin to cool
temperatures down first along the nrn CA coast while the rest of the
region remains under the influence of the back side of the ridge as
it heads further inland. Afternoon highs for Friday at +5 to +15 deg
F above normal with some areas up to +20 deg F above normal. By
early Saturday, a broader trough will set up just offshore of the
west coast before quickly splitting into two systems. The northern
most half will form an upper trough that travels through the PacNW
the rest of Saturday while the southern half closes off into an
upper low offshore of CA. Models have the low moving southeast
towards southern CA, but both the GFS/ECMWF keep the system offshore
the rest of the extended. There are already some differences in the
position of the system when it forms that will impact when it
eventually reaches land. For now, any additional precip would be
from the trough to the north on Saturday but amounts expected to be
fairly minimal. The offshore troughing will continue to lower
temperatures from west to east for Saturday as well with much of CA
closer to normal.

QPF from the troughs moving through the PacNW late this week and
into the weekend. Little to no precip south of Shasta and generally
0.10" or less for the north coast and inland along the OR border.
Possibly up to 0.25" at the crest of the Cascades. Freezing levels
10.5-13.5 kft for Thursday from the OR border to the Sierra lowering
nw to se into Friday down to 6.5-11.5 kft north of I-80 mid morning.
Freezing levels will continue to decrease into the weekend down to 5-
9.5 kft north of I-80 mid Saturday morning and 9.5-12.5 kft from I-
80 to the southern Sierra. Higher freezing levels will spread up the
coast the rest of the day sending 10 kft up into Shasta and the
foothills.

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



Osborne/AS

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