Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
FXUS66 KHNX 192201
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
301 PM PDT Sun Mar 19 2017
.SYNOPSIS...An upper low pressure system will spread moisture
into the area by Monday night with increased precipitation chances
on Monday Night and Tuesday. Unsettled conditions and cooler
temperatures will then prevail for the remainder of the week.
.DISCUSSION...The large area of high pressure that provided for
dry conditions and an unseasonably warm airmass over our area for
the past several days has broken down as a large Pacific low
pressure system is approaching CA. Temperatures across our area
are trending downward by 4-8 DEG F from yday as high clouds are
streaming across central CA in a southwest flow aloft.
12Z WRF indicating the low will push inland across Norcal and the
PAC NW Monday night and Tuesday which will spread increasing deep
moisture and dynamics into central CA resulting in precipitation
spreading southward across our area Monday night through Tuesday
morning. With a warm airmass prevailing through early Tuesday
afternoon snow levels will be high (between 8000 and 9000 feet
over the Southern Sierra Nevada). The precipitation will become
more showery in nature late Tuesday as a cold front pushes
southward. Thunderstorms will be also be possible across our area
on Tuesday afternoon in the colder post-frontal airmass most
noticeably in the central San Joaquin Valley where LI/s of -7 to
-4 DEG C and CAPES of 1000 to 1500 J/KG are progged. The showery
regime will continue across our area through Wednesday as the
upper trough axis pushes east across CA. The WRF is still
indicating 500 mb temperatures of -26 to -24 DEG C over our area
Wednesday afternoon along with increased instability and CAPES. As
a result will mention the potential for thunderstorms for our
area on Wednesday as well. The main threats from these
thunderstorms on Tuesday and Wednesday will be locally heavy
rainfall, street flooding, hail and frequent lightning. Snow
levels will plummet to 5000 to 6000 feet in the colder post-
frontal airmass on Wednesday.
The medium range models are in fairly good agreement with
shortwave ridging prevailing over our area Thursday and Thursday
Night which will provide our area with a short respite from the
active weather. A cold and moist upper trough is progged to push
into the western CONUS on Friday and cross the region on Saturday
which will result in a period of precipitation and cooler than
normal daytime temperatures. This late week system has the
potential to produce significant precipitation across our area
with with models continuing to advertise 1-3 inches of liquid
precipitation over the Southern Sierra Nevada. A shortwave ridge
will follow on Sunday, but the longer term models are indicating
the potential for additional storms impacting our area the
.AVIATION...Increasing areas of MVFR and local mountain obscuring
IFR in low clouds over the higher elevations of the Southern
Sierra Nevada after 18Z Mon. Otherwise, VFR conditions can be
expected across the Central CA Interior during the next 24 hours.
.AIR QUALITY ISSUES...None.
The level of certainty for days 1 and 2 is medium.
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.