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Area Forecast Discussion (AFD)

Issued by San Joaquin Valley, CA (HNX)

FXUS66 KHNX 201047

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
347 AM PDT Fri Oct 20 2017

.SYNOPSIS...A storm system moving through today will bring light 
precipitation, gusty winds and much cooler temperatures. The storm
will exit the region tonight with dry conditions and a warming 
trend this weekend into the middle of next week.


.DISCUSSION...Precipitation is finally beginning to spread into
central California at this time. Radar imagery shows the leading
edge of the frontal band just reaching Yosemite NP and stretching
southwest across Merced County. The latest hi-res models show the
front reaching Kern County by around sunrise. Mostly light precip
is expected but briefly moderate, especially in the mountains due
to orographic enhancement. QPF is up to one quarter of an inch in
the Sierra around Yosemite NP and up to one tenth of an inch south
through the Tehachapi Mountains. The SJ Valley will generally see
only a few hundredths of an inch though a few locations may see 
as much as a tenth of an inch. The snow level is currently around 
9500 feet in Yosemite NP, but will lower to around 8000 later over
the next few hours. Snow amounts of 1-3 inches will be possible 
around Yosemite NP, with a dusting to 1 inch southward. Most of 
the activity will end by Noon though some light upslope showers 
are possible from the Tehachapi mountains up to around Sequoia NP.

Windy conditions are already occurring through and below passes 
in the Kern County mountains and desert as onshore surface 
pressure gradients increase. A Wind Advisory is in effect for 
these areas through 11 PM tonight. Several gauges are measuring 
gusts around 40-50 mph over the last few hours. Gusty conditions 
will develop across the SJ Valley as well as the front moves 
through. Gusts of 20-30 mph are expected through this evening. 
Winds will diminish overnight into Saturday morning.

This system is bringing in a much cooler air mass so temperatures
will be well below normal today. Highs in the SJ Valley will be in
the upper 60s in most areas, around 10 degrees below normal. Parts
of the Sierra could see temperatures 15-20 degrees below normal.
The trough will quickly exit to the east on Saturday but a cool
northwesterly flow aloft will continue. Models agrees with strong
high pressure building in through the middle of next week for a 
warming and drying trend. Highs are forecast to be back to around 
normal on Sunday then climbing to about 10 degrees above normal on
Tuesday and Wednesday. An upper trough is projected to drop down
from Canada over the Rockies later next week and weaken the ridge
for some slight cooling.


Areas of MVFR and local IFR conditions with mountain obscurations in 
clouds and precipitation through 18Z, then local MVFR in clouds and 
showers in the mountains through 00Z Saturday. Wind gusts 40-50 KTS 
over the Sierra crest and in the Kern County mountains through 06Z 





The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is high.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.


.HNX Watches/Warnings/Advisories...
Wind Advisory until 11 PM PDT this evening CAZ095-098-099.