Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
FXUS66 KHNX 221302
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
502 AM PST Wed Feb 22 2017
.SYNOPSIS...A much cooler air mass will move into the central
California during the next few days. Isolated showers can be
expected in the San Joaquin Valley today with more numerous rain
and snow showers over the mountains. Dry weather will prevail
Thursday through Friday night. Another storm will bring a
return of rain and mountain snow to the region this weekend.
.DISCUSSION...An upper level trough is poised just offshore
this morning. Its presence has cooled the atmosphere considerably
across the CWA since yesterday morning as temperatures are
trending a good 5 to 15 degrees lower than 24 hours ago. A
strong southwesterly flow aloft is still generating orographic
lift and quite a bit of shower activity along the west slopes
of the Sierra with snow levels in the Sierra averaging close to
4500 feet. A weak deformation zone currently exists across Fresno
County and is helping to produce a few light showers in the
central portion of the San Joaquin Valley.
The models bring the upper level trough inland today which in
turn will generate additional showers over the mountainous
terrain. Although isolated showers are still possible in the
San Joaquin Valley today, it finally looks like the trend to
drier weather will finally take place, especially across the
western third of the valley. The south end of the valley will
take a little longer to dry out where a few residual showers
could linger into this evening. Otherwise, northwesterly breezes
will bring a cooler air mass into the region during the next 24
hours. Winds will gust to advisory levels in the Kern County
desert by this afternoon and remain gusty through tonight as the
upper level trough exits into the Great Basin. Meanwhile, upslope
precipitation will occur in the Kern County mountains, falling as
snow showers above 5,000 feet today. The arrival of colder air
this evening will bring snow levels down to pass level in Kern
County where a small accumulation of snow is possible before
daybreak Thursday. A Winter Weather Advisory was issued
accordingly for the Kern County mountains. Motorists planning
travel over the Grapevine from this evening through Thursday
morning should be prepared for slick driving conditions. I-5 over
Tejon Pass and Highway 58 through Tehachapi Pass could become icy
and/or snow covered tonight.
A brisk northwesterly flow aloft will continue over central
California Thursday with clouds lingering along the west slopes
of the Sierra and north facing slopes of the Tehachapi mountains
for much of the day. The west side of the San Joaquin Valley as
well as the Kern County desert will remain breezy through Thursday
afternoon. As winds tame in the valley Thursday night, temps
will drop off pretty rapidly. Frost is possible in the coldest
locations of the valley early Friday morning in addition to patchy
dense fog. No doubt it will be our chilliest morning since late
January. Otherwise, weak upper level ridging will bring a
continuation of dry weather to the central California interior
Friday through Friday night.
Another storm system will threaten central California with another
round of wet weather this weekend. The models position this storm
near the northern California coast Saturday. An undercutting jet
will transport the brunt of this moisture into the cwa from Sat
evening into Sunday evening. Like past storms, the heaviest precip
will fall perpendicular to the upper level jet, so the west slopes
of the Sierra could get slammed again with significant rain and
higher elevation snow. The good news is that snow levels will be
in the respectable 5,000 to 6,000 foot range this weekend. Below
that elevation, a recurrence of flooding is possible and water
levels will have to be monitored closely on area rivers and
The weekend storm and its associated upper level trough are
forecast to move inland over California early next week. So
Monday and Tuesday will be cooler but remain unsettled with the
best chance of showers over the foothills and mountains. Snow
levels should lower to between 4,000 feet and 5,000 feet by then.
The longer range models forecast an EPAC ridge to gradually build
into California during the middle of next week with at last a
return of dry weather. This ridge should dominate the pattern
during the 7 to 10 day period.
.AVIATION...MVFR conditions can be expected along west facing slopes
of the Sierra and west and north facing slopes of the Tehachapis
through 00z Friday, with local IFR and mountain obscurations in
heavier precipitation over the higher elevations through 06z
Thursday. Winds will gust over 40 KT across the mountain and desert
areas of Kern County through 09z Thursday. VFR conditions will
otherwise prevail across the central California interior during the
next 24 hours.
.AIR QUALITY ISSUES...
The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.
Winter Weather Advisory from 8 AM this morning to 11 AM PST