Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Joaquin Valley - Hanford California
300 PM PST Thursday Nov 27 2014
high pressure will weaken allowing a weather disturbance to pass
across mainly northern California Friday night through early Sunday.
High pressure will then rebuild over the region Monday before a
potentially much stronger storm system moves in on Tuesday.
Discussion...a quiet weather regime will continue over the
central California interior through Friday as an upper level ridge of
high pressure centered off the Baja California coast remains in control.
During this time...skies will be mostly clear (nothing more than
some cirrus) and the weather will remain dry. Folks heading out
to do some shopping on black Friday can expect mild afternoon
temperatures and if they are out and about in the early morning
hours...they will have to deal with patchy dense fog in the sj valley.
The remainder of the Holiday weekend will trend cloudier...especially
across the northern half of our County Warning Area as the high pressure ridge
flattens and a zonal flow aloft becomes established over central
California. A couple of weak disturbances embedded in the the westerly
flow will brush the northern half of our County Warning Area with light precipitation
this weekend. The first one will move through Saturday afternoon
and the second one will be right on its heels Sunday. Once the
second disturbance exits into the Great Basin Sunday evening...
the upper level ridge will build northward again. Although the
ridge may be dirtied by middle and high clouds...it will keep our
weather dry Monday through at least Monday evening.
Afterward...our attention will turn to a developing storm system
over the eastern Pacific. The models are still having difficulty
handling the evolution of this storm and the eastward movement of
its precipitation next week. Although these discrepancies lower our
overall confidence in the 4 to 7 day period...we still believe
the storm will bring significantly wet weather into the central California
interior by the middle of next week. The ecm is slowest of all the
operational runs and holds the upper level ridge over the County Warning Area through
Tuesday while the GFS shifts it into the Great Basin. Whatever the
case...a southwesterly flow aloft will inevitably develop over
central and Southern California with the potential to transport a rich
supply of moisture...possibly tropical in origin...into our County Warning Area.
The south facing slopes of the Tehachapi Mountains and west facing
slopes of the Sierra will likely receive the heaviest precipitation
thanks to orographic lift but not without the risk of flooding...
particularly over the burn scars. Snow levels will remain high
during the storm...generally above 7500 feet...with upwards of
2 feet or more possible near the Sierra crest. On the other
hand...a strong SW flow aloft will also cause some rain shadowing
on the west side and south end of the sj valley. Right now it appears
the most favorable window of high quantitative precipitation forecast will be from late Tuesday
through Wednesday but this could change if the models continue to
slow the eastward progress of the storm. There was a concern that
if this trend with the models continues...the storm would stall so
far offshore that it would not be able to bring its precipitation
into the central California interior. Today that is just a remote
possibility. We hope we can abolish that idea by tomorrow. The
changes that were made to our forecast today were to slow down the
arrival of precipitation next week. Quantitative precipitation forecast was lowered a bit and blended
with model quantitative precipitation forecast and weighed input from wpc and the cnrfc. The
slower timing also means that preciitation may linger through
next Thursday. By then...the models forecast this storm to exit
into the Great Basin.
The latest ensemble forecast also favors a slower but more
southerly track of this storm and actually dampens this system
over Southern California by Tuesday evening as it becomes absorbed in the
southern branch of the jet stream. By midweek...the ensembles
forecast a split flow pattern to develop along the West Coast with
central California right in the middle of it. Historically...split flow
patterns rarely offer Promise of wet weather in central California...so
we will just have to wait and see. Hence the reason for low
forecaster confidence in the extended periods.
Aviation... in the San Joaquin Valley...widespread MVFR
visibilities in haze. Areas of IFR visibilities in mist and local
LIFR in fog from 09z Friday to 17z Friday. Otherwise...VFR conditions
will prevail across the central California interior during the next 24
Air quality issues...
on Friday November 28 2014... 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
The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is low.
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 11-27 78:1959 47:1972 54:1985 27:1948
kfat 11-28 76:1891 46:1972 52:1966 28:1969
kfat 11-29 76:1947 47:1905 58:1901 26:1975
Kbfl 11-27 85:1901 46:1972 54:1904 28:1905
kbfl 11-28 82:1993 46:2000 55:1904 28:1905
kbfl 11-29 80:1924 51:2006 57:1938 28:1919