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AGUS76 KRSA 142112
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
130 PM PST Thu Nov 14 2024

...COOL WITH OCCASIONAL SHOWERS INTO MONDAY...

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

Little change (a tenth of an inch or less) to the afternoon forecast
except increased amounts up to a quarter of an inch for portions of
the Shasta Basin and into Nrn Sierra for this afternoon/evening.

Upper level trough digging just off the west coast today and will
move onshore this afternoon into tonight with the trough over the
western U.S. on Friday then the trough becomes positively tilted
with high pressure building into Nrn and Central CA and NV and a low
forming over Srn CA on Saturday and then the low moving into Baja
Saturday night as another system approaches the north. Scattered
showers over Srn OR and Nrn CA this afternoon will spread south and
east into Srn CA and Wrn NV tonight as the trough moves onshore.
Isolated thunderstorms possible this afternoon and evening over Srn
OR and Nrn CA. Highest precipitation totals for today into tonight
expected along the Nrn CA coast and Srn OR Cascades and Shasta basin
and along the Sierra and Tehachapis with amounts generally around
0.2-0.65 inches with local amounts up to an inch. Max temperatures
near normal to below normal up to 15 degrees over the region this
afternoon. Freezing levels around 4000-5000 ft near the ORCA border
and around 5500-7000ft over Nrn Sierra today then dropping to around
3000-4000 ft near the ORCA border and 4000-6000ft over the Sierra
and around 5000-7000ft over Srn CA tonight. Showers mainly along the
Sierra and east over Nevada and over Central and Srn CA on Friday.
Heaviest precip expected over the Central and Srn Sierra and over
Central and Ern NV and Tehachapi Mtns and San Bernardino Mtns and
south to San Diego County Mtns with amounts around 0.2-0.6 with
local amounts up to around 0.75 inches. Overnight temperatures near
normal to around 10 degrees below normal Thursday night. Max
temperatures around 5 to 20 degrees below normal on Friday. Freezing
levels generally around 3500-6000ft over the region on Friday and
dropping to 3000-5000ft Friday night. Showers taper off Friday night
into Saturday with lingering showers possible mainly over San
Bernardino and south to San Diego County and over Ern NV during the
day Saturday.  Precip ahead of the next system starts to move into
NW CA and the Srn OR Cascades Saturday night as precip diminishes
over the far South as the low moves into Baja. Lows Friday night
around 5 to 15 degrees below normal. Max temperatures on Saturday
around 5 to 20 degrees below normal with the coldest temps over Srn
CA and into NV. Freezing levels rise on Saturday as high pressure
build into the region with Freezing levels rising over srn CA around
6000 ft and above 800ft over Nrn CA coast and Srn OR Cascades
Saturday evening.

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

Minimal changes to the forecast for the afternoon update. A front is
still expected to send precip to northern CA, srn OR, and nrn NV
Sunday into early next week. The same model differences that existed
this morning remain in place. The GFS continues to show a shallower
trough following the front while the ECMWF digs the trough deeper
across CA/NV spreading precip further south than the GFS. A handful
of both model ensemble members are continuing to show precip
sneaking into nrn CA into Wednesday while the det runs remain dry
under high pressure.

The afternoon QPF was a blend of WPC guidance and the latest NBM
with changes on the order of a few hundredths to a tenth of an inch
locally from the morning forecast. Precip totals are forecast to be
highest around the Smith Basin and srn OR Cascades with showers
extending through the central coast. Majority of the precip in the
extended is expected Sunday into Monday. QPF totals: 0.75-1.50"
north coast/srn OR Cascades (locally higher Smith Basin), 0.10-0.40"
Shasta and along the OR border as well as over the nrn Sierra, and a
few hundredths to a tenth of an inch or so for the central/srn
Sierra Greater Bay Area and down the valleys.

Freezing levels will lower from nw to se into Monday from 7-10.5 kft
across CA Sunday down to 3-5.5 kft north of I-80 and 5-10 kft to the
south Monday. How long lower freezing levels stick around and how
far they spread will depend on the 500 mb height pattern which at
this point is still a subject of disagreement between the ECMWF and
the GFS.


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



Osborne/AS

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