Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
FXUS66 KHNX 261151
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
451 AM PDT WED OCT 26 2016
Weak high pressure will remain over the region today for warm and
dry conditions before a strong Pacific weather system moves in
Thursday afternoon and Friday bringing widespread rain and high
.DISCUSSION...Another quiet night across central California with
satellite imagery showing mainly clear skies overhead. Upper ridge
over the four corners region and an East Pacific trough providing
southwest flow aloft with a rich moisture feed into the Pacific
Northwest. The pattern will amplify further today with the ridge
building over the Rockies. This will keep dry conditions across
the district with temperatures nudging upwards again. Highs today
are forecast to be several degrees above normal for late October
with lower 80s in the San Joaquin Valley and Kern County Desert.
Short wave at the base of the trough will dig down just south of
30N and begin to draw up a plume of sub-tropical moisture tonight.
In addition...moisture from Hurricane Seymour is expected to get
entrained in the southwest flow as well. This nearly 2" PWAT plume
is forecast to move towards the central CA coast on Thursday as
the s/wv begins to shift northeast. There remains some uncertainty
with the timing and QPF amounts, but it does look like a widespread
precipitation event is shaping up. Based on latest model trends,
onset of precip may hold off until Thursday afternoon, with the
bulk still expected to be from Thursday evening through Friday
morning. Current forecast calls for up to an inch of rainfall in
parts of the San Joaquin Valley north of Fresno County. While
most of the Valley can expect from a quarter to a half of an inch,
with the south Valley generally seeing the lower amounts. The
Southern Sierra may see upwards of 2 inches rainfall around
Yosemite. Amounts decrease as you go south with the Kern County
Mountains forecast to see from one half to one inch. The Kern
County Deserts may see one to two tenths of an inch. Again, model
QPF varies quite a bit so confidence in amounts is not great. This
southwest feed aloft will mean snow levels remain high. The majority
of the event will see snow levels above 10,000 feet. But as the
s/wv moves inland on Friday morning, snow levels should lower to
near 9,500 feet around Yosemite NP with accumulating snow possible
along Tioga Pass.
The s/wv quickly lifts northeast Friday aftn/night with showers
tapering off as a much drier WSW flow aloft moves in. The deep
Gulf of Alaska low is expected to drop down of the PACNW coast on
Saturday then begin to shift inland over NorCAL on Sunday. Cannot
rule out some light rain on Saturday but most areas should remain
dry. Rain chances ramp up again on Sunday but the focus will be to
the north. This northern latitude airmass will lower snow levels
down to around 8K feet on Sunday, then possibly 7K feet by Monday
morning as precip winds down. Another upstream s/wv is shown to
move in around Monday night and Tuesday for yet another shot at
precip. But there is low confidence on the track of this wave.
Southwesterly flow will ramp up winds over the mountains Thursday
night and Friday with strong gusts over ridges and through some
mountain passes. Breezy to gusty conditions will continue through
the weekend. Temperatures will lower to near normal Thursday then
a little lower Fri/Sat. A colder air mass moves in on Sunday for
temps falling to several degrees below climo.
VFR conditions can be expected for the central California interior
during the next 24 hours.
.AIR QUALITY ISSUES...
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is low.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.