133
FXUS66 KSTO 181033 AAA
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
130 AM PDT Sat May 18 2024

.SYNOPSIS...
Seasonable temperatures will continue through the weekend and into
early next week. Mostly sunny and dry conditions with periods of
breezy winds expected through the next 7 days. Isolated showers
and thunderstorms over high Sierra south of Highway 50 today.

&&

.DISCUSSION...
Synoptically, west-southwest flow will continue to keep onshore
winds through Saturday morning. Latest GOES-18 Nighttime
Microphysics RGB indicates the marine low stratus deck is pushing
inland into the Delta region. Hires guidance is not handling
current trends well. Based on current 20-30 mph Delta winds and
already apparent intrusion of stratus deck, continued eastward
push of stratus looks probable with potentially similar coverage
by sunrise to what was observed yesterday with areas around or
just west of the Greater Sacramento Metro.

Besides possible morning stratus, expect a mostly clear Saturday
with continued breezy onshore winds through Saturday night, though
not as strong as Friday night.

Only other weather of note will be the isolated shower and
thunderstorm chances along the Sierra crest mainly south of
Highway 50 this afternoon- evening where NBM has 15-30%
probabilities of thunderstorms. Best chances will be in
southeastern Tuolumne County today where hires indicates decent
instability will develop with little/minimal CIN. No significant
forcing besides the mountains themselves, so main impacts expected
with any thunderstorm will be brief heavy rain, locally gusty
winds, lightning, and small hail with the stronger updrafts. Given
west- southwesterly flow aloft and mean winds around 10 knots,
thunderstorms will drift eastward after forming.

Throughout the day today, a trough from the British Columbia will
dig into the Great Basin region, which will shift a more westerly
flow to a northwesterly flow overhead tonight-Sunday. As this
trough phases with a closed upper-low in SoCal Monday, pressure
gradients across NorCal will increase, producing another breezy
north wind day. Currently the NBM has a 50-75% probability of
gusts greater than 34 knots (~40 mph) in the usual north wind
prone area in the western Sacramento Valley along the I-5
corridor. Current forecasts continue to keep gusts only to around
25-30 knots, but given the probabilities of higher winds, winds
may increase as we get closer.

Per usual with north wind days, minimum afternoon RH`s will
decline, with widespread less than 15% RH values in the Sacramento
Valley. Temperatures will be mild, but breezy winds and low RH`s
will lead to locally elevated fire weather conditions Monday.

Northerly flow will weaken Tuesday, allowing temperatures to
increase but winds to decrease. Tuesday appears to be the warmest
day in the next 7 days, with highs in the mid 80s to low 90s
across the Valley/Delta and upper 60s to low 80s in the
Foothills/Mountains.

//Peters

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Series of upper lows progged to move through the PacNW during the
extended forecast period. Associated upper troughing will extend
into NorCal. Models differ with timing, track, and strength of
lows leading to some forecast uncertainty with precipitation
potential. NBM shows some showers chances over our northern and
eastern foothills/mountains Friday and Saturday afternoon. High
temperatures forecast to cool through the extended period,
returning to near normal Friday, and slightly below normal
Saturday.

&&

.AVIATION...
VFR conditions over interior NorCal next 24 hrs except areas
MVFR/IFR in stratus vcnty of Delta til 18z and locally in Sac Vly
til 17z. In Central Vly, sfc wind mainly at or below 12 kts til 00z
Sat, then areas sfc wind up to 20 kts. Vcnty Delta SWly sfc wind 15-
25 kts with lcl gusts to 35 kts. Isolated -shra/-tsra possible over
SierNev, S of Hwy 50 btwn 19z-02z.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$