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AGUS76 KRSA 072130
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
130 PM PST Thu Nov 7 2024

...DRY CONDITIONS THE REST OF THE WORK WEEK AS HIGH PRESSURE SITS
OVER THE EASTERN PACIFIC...
...POTENTIAL FOR LIGHT PRECIP OVER THE WEEKEND FOR NW CA & SRN OR
WITH MORE WIDESPREAD PRECIP POSSIBLE EARLY NEXT WEEK...

.METEOROLOGICAL CONDITIONS (SHORT TERM: THU PM - SUN AM)...

No changes to the afternoon update for the short term forecast.
Everything remains on track, still have a large upper ridge
stretched across the eastern Pacific and into the west coast
bringing dry conditions to the region. An upper low remains off to
the east over the Four Corners and will begin to move off towards TX
early tomorrow morning. The exiting of the upper low will allow the
ridge to push further inland spreading near to just above normal
temperatures across CA and NV. A weak system is still progged to
arrive over the weekend with continued model disagreement. The 12z
GFS still has a separated shortwave moving into the PacNW with
another sw/ne oriented trough heading for northern/central CA while
the ECMWF is showing a more cohesive trough without that level of
separation. The result is the 12z det ECMWF continuing to predict
more widespread light showers along the northern CA coast and srn OR
while the GFS is mainly dry. Fewer of the 12z ECMWF members are
showing precip compared to this morning and the ensemble spread has
cut in half more closely matching the 0 to 0.50" out of the GFS. The
morning forecast already leaned on the dryer side, so not much
change was needed for the afternoon. Still predicting a few
hundredths to a tenth of an inch along the north coast and srn OR
Cascades Saturday night with dry conditions elsewhere.


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

Models still vary but weaker with shortwave on Sunday with light
precip possible mainly over Srn Or Cascades and in Smith Basin into
Sunday afternoon. A system drops down from the Gulf of Alaska to the
West coast Sunday night into Monday (EC farther south than GFS) then
into the Rockies/ Great Basin on Tuesday. Precip tapers off on
Tuesday in between systems with precip mainly across the north and
along the Sierra as trough shifts to the east. General trend of
decreasing amounts and trimming southern extent. Still uncertainty
in amounts and southern extent. 40% of ensemble members (Canadian
65% GFS 20%, EC 42%) for 24hr QPF 50th Percentile clusters ending
12Z Tuesday keep precip to around the I-80 corridor and north and
precip amounts up to 2 inches for Smith basin and up to 1.5 inches
for the Sierra and 34% of members (Canadian 25% GFS 13% and EC 50%)
spreading precip south to around Point Conception and along the
Sierra with precip amounts up to 3 inches for the Smith Basin and
around Cape Mendocino and Nrn Sierra and the other 26% of members in
between with precip south to around Monterey Bay and into Central
Sierra. The forecast uses the latest nbm and wpc for QPF amounts in
current forecast 2-3.5 inches Smith Basin and 1-2 inches around Cape
Mendocino and generally 0.75-1.25 for the Shasta Basin and Nrn
Sierra and 0.25-0.75 inch for the Russian and Central Sierra and 0.2-
0.6 for Sac Valley and 0.1-0.5 inches Srn Sierra and Santa Cruz Mtns
and Big Sur Coast and a quarter of an inch or less for SJ Valley and
generally half an inch or less over NV.

Freezing levels around 7500 ft near ORCA border Sunday morning and
rise to around 9000ft Sunday afternoon then drop to around 6000 ft
Monday morning and around 5000 ft in the afternoon. Freezing levels
above 9000ft over the Sierra then drop to 6000-7000ft over the Nrn
Sierra  and 7000-8000ft over the Central Sierra Monday afternoon and
5500-6500ft for the North and 7000-8000ft for Central Sierra Monday
evening. Freezing levels around 5000ft over Nrn CA and 5000-7000ft
over Nrn and Central NV on Tuesday morning then rising to around
7000ft near the ORCA border and above 8000ft over the Sierra.


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



AS/Osborne

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