Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Joaquin Valley - Hanford California
936 PM PST sun Dec 21 2014
Update...increase drizzle and light rain in the valley and lower
foothills this evening.
a ridge of high pressure will continue to build into central
California during the next few days. Spotty light precipitation is
still possible through tonight in the Kern County mountains.
Meanwhile...much of the San Joaquin Valley will be plagued with low
clouds through Tuesday along with patchy dense fog and drizzle each
night and morning.
Discussion...a very weak impulse passing through the area is
adding some synoptic lift and helping to squeeze out some drizzle
and very light rain across the San Joaquin Valley and lower
elevations of the foothills. A few locations...mainly in enhanced
upslope areas...are measuring up to a couple of hundredths of an
inch. A minor update to the forecast accounts for this area of
light precipitation. This scenario would seem to make the development of
dense fog less likely. The current dense fog advisory which begins
at midnight is thus being carefully evaluated. Models move the
very weak positive vorticity advection out after midnight and conditions may yet stabilize
sufficiently to see early morning dense fog development. For now
we will keep the dense fog advisory in effect.
Previous discussion... /issued 305 PM PST sun Dec 21 2014/
as the fog dissipates this afternoon from Merced to Fresno...fog
and low clouds are now piling up against the Tehachapi/Grapevine/
range as the flow moves the moisture southward. The northwest
flow aloft is expected to weaken tonight as the building high
pressure ridge moves further onshore. This weakening of the wind
flow aloft will allow the moisture piled up at the south end the
valley to flow back across the San Joaquin Valley for another
night of clouds and dense fog.
While short range mesoscale-scale models show a change is visibilities
as fog and haze decreases...the models show almost no change in
the surface relative humidities across the San Joaquin Valley in
the next 24 hours. This lack of change translates in a very high
potential for fog development over the lower elevations of the
central California interior. Therefore...will go ahead a issue
another dense fog advisory tonight from near midnight to around
1000 am PST Monday morning.
By Monday...models show a high degree of confidence in a solution
that strengthens the ridge with its axis just off the Pacific
coast. This pattern will keep the region dry with persistent
clouds and fog over the San Joaquin Valley. The stagnant pattern
may see some change by midweek as models attempt to move an inside
slider through northern California/Great Basin toward Wednesday.
While confidence is low with the midweek trough...will keep a
slight chance of possible precipitation over the Sierra Nevada and areas
north of Fresno County. Timing issues are the main concern with
the midweek system that is expected to exit out of California on
Thursday. Afterward...the ridge rebuilds until next weekend. By
next Sunday...uncertainty is too high to deviate much from climatology.
Therefore...will opt for near climatology on day seven.
in the San Joaquin Valley...widespread MVFR and areas of IFR in
mist/haze and low clouds with LIFR conditions becoming prevalent in
fog between 06z Monday and 12z Monday. In the Tehachapi Mountains....areas
of IFR and local LIFR in upslope low clouds along the valley facing
slopes. Otherwise VFR will prevail over the central California interior for
the next 24 hours.
Air quality issues...
on Monday December 22 2014... fireplace/wood stove burning status
is: no burning unless registered in Fresno County.
Further information is available at valleyair.Org
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.
This information is provided as part of a trial project conducted
by the National Weather Service San Joaquin Valley - Hanford.
Certainty levels include low...medium...and high. Please visit
www.Weather.Gov/hnx/certainty.Php /all lower case/ for additional
information and/or to provide feedback.
site date hi_max:year lo_max:year hi_min:year lo_min:year
Kfat 12-21 71:1955 34:1998 54:1964 23:1897
kfat 12-22 70:1964 35:1998 57:1955 19:1990
kfat 12-23 68:1964 37:1928 60:1964 18:1990
Kbfl 12-21 78:1919 36:1998 59:1977 23:1905
kbfl 12-22 76:2005 34:1998 56:1977 20:1990
kbfl 12-23 73:1964 36:1928 63:1955 14:1905
dense fog advisory until 10 am PST Monday caz089>092.