Dense Fog in California, December 18, 2018

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
427 AM PST Tue Dec 18 2018

.SYNOPSIS...High pressure will move into the the region today and
keep dry weather across our area through Thursday. Areas of night
and morning fog will be possible in the San Joaquin Valley. The
high will weaken on Friday as a low pressure system moves north
of our area.

&&

.DISCUSSION...The low pressure system that was responsible for
Monday's rain and higher elevation snow has moved well to the east
of our area and is now centered over New Mexico. High pressure is
now building into central CA although some upslope low clouds
remain over the south end and east side of the San Joaquin Valley
and along the valley facing slopes in the Kern County Mountains.
Some of these upslope clouds formed fog banks Monday evening over
the Kern County Mountains and impacted travel on Interstate 5
which prompted the issuance of a Dense Fog Advisory during the
evening. However, the fog has since dissipated and the Dense Fog
Advisory has been cancelled.

WV imagery is showing a strong upper jet taking aim at the PAC NW.
IR showing high clouds from this jet spilling into central CA as a
potent shortwave pushed through the PAC NW. The main impact that
this shortwave will have for our area is that it will provide for
enough mixing to inhibit the formation of widespread dense fog
over the San Joaquin Valley this morning although some patchy fog
is still possible in areas which clear out.

The fog will likely be more prevalent over the San Joaquin
Valley on Wednesday and Thursday as high pressure builds inland
and strengthens over our area. The remainder of our area will be
dry with above normal temperatures. The high will weaken and break
down on Thursday Night as an elongated shortwave trough pushes
through CA. RH progs are showing the deeper moisture sufficient
for precipitation remaining north of our area as this system
pushes through.

The medium range models are in fairly good agreement with a zonal
flow pattern prevailing over the western CONUS Friday through
Sunday. The individual impulses will be difficult to time, but
thye operational GFS and ECMWF keep the main storm track north of
our area during this period although some light precipitation
will be possible from Fresno County northward on Sunday. A
potentially stronger system may impact our area next Monday Night
and Christmas Day and provide our area with some significant
precipitation.

&&

.AVIATION...In the San Joaquin Valley, expect areas of MVFR
visibilities due to haze and mist along with local IFR/LIFR in fog
through 18Z Tuesday and again after 06Z Wednesday. Local terrain
obscuration in low clouds is also possible along adjacent north
and west facing slopes. Otherwise VFR conditions will prevail over
central California through the next 24 hours.

&&

.AIR QUALITY ISSUES...None.

&&

.CERTAINTY...

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.html for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...NONE.

&&

public...DS
avn/fw...JEB
synopsis...DS

weather.gov/hanford