Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 141029
AFDHNX

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
229 AM PST Thu Dec 14 2017

.SYNOPSIS...High pressure will remain over the region today
and Friday. A weak weather disturbance will drop into the Great
Basin on Friday night and Saturday bringing a small threat of
precipitation to the Sierra crest near Yosemite.

&&

.DISCUSSION...North winds aloft are generating some clouds over
Sierra as they interact with the mountains otherwise skies are
clear for potential viewing of the meteor shower. Dry air
continues to be locked in place over the region in the lower
levels with lots of single digit humidity values over the Sierra
and Kern County mountains and desert areas. The Red Flag Warning
for low humidity and dry fuels will remain in place.

In the bigger picture satellite imagery shows the big ridge
firmly in place along the West Coast with the axis stretching from
Seattle to San Francisco. Over the next couple of days, forecast
models try to change the low wave pattern over the CONUS with the
ridge axis shifting a little to the east, allowing an incoming
Gulf of Alaska trough to ride southeast into the region on Friday
night and Saturday. Latest GFS model brings the trough axis into
Central California on Friday night however little to no
precipitation is projected at this time outside the Yosemite area.
What this trough will likely be much better at then generating
precipitation will be to bring enough colder air in the mid levels
to finally break down the very persistent and strong inversion
which has been locked into place for the past week or longer.

Model soundings indicate about 20 degrees of cooling in the
4000-6000 foot above sea level layer from Friday through Saturday
night and this just may be change in temperature to fully break
the "capping inversion" and allow some northerly winds aloft to
mix to the surface and clear out the tremendous haze and pollution
layer which has been plaguing the San Joaquin Valley and lower
foothills for some time. Precipitation would be nice...but a
change of airmass may have to suffice.

Beyond this weekend, models again rebuild the Pacific Northwest
ridge and keep a rather chilly northerly flow aloft going into
Tuesday. GFS model then drops an area of low pressure and
assoicated cold airmass from Western Canada into the Pacific
Northwest Tuesday night and Wednesday while pushing a weakening
cold front southward into Northern California. This is all
occuring as the cold low pressure system begins to head east
across the Northern Rockies...leaving a dry but cold trough over
Central and Southern California into next weekend. Based on the
pattern thus far this fall, this solution seems to be the most
consistent and reasonable.

 ***It should be noted for those looking (or possibly even
  wishing) for a much more substantial weather event with very
  cold temperatures and some snow, the ECMWF again sends a very
  deep and cold low into Southern California on Christmas Eve.
  Thus far the ECMWF has a very poor track record of consistently
  projecting closed lows into the region with little of no model
  to model continuity. Confidence in this outlier is very minimal
  at this time. ***

&&

.AVIATION...
Widespread MVFR visibility in haze and mist will persist in the San
Joaquin Valley, with areas of IFR and local LIFR/VLIFR in fog
developing until 18Z. Otherwise, VFR conditions will prevail over
the central CA interior during the next 24 hours.

&&

.AIR QUALITY ISSUES...
On Thursday December 14 2017... Unhealthy for sensitive groups in
Fresno... Kern... Kings and Tulare Counties. Fireplace/Wood Stove
Burning Status is: No Burning Unless Registered in Fresno...
Kern... Kings... Madera... Merced and Tulare Counties. Further
information is available at Valleyair.org

&&

.CERTAINTY...

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

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...
Red Flag Warning until 8 PM PST Friday CAZ295>297.

&&

$$

public...Dudley
avn/fw...BSO
synopsis...Dudley

weather.gov/hanford



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