Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Joaquin Valley - Hanford California
325 am PDT sun Apr 19 2015
an upper level area of high pressure is producing dry conditions and
above average temperatures through the weekend for the valley and
foothills. A threat of thunderstorms does exist along the crest of
the Sierra Nevada through Tuesday. An upper level area of low
pressure moves south along the coast Wednesday through Friday. This
will bring a threat of showers and thunderstorms to the entire
central California interior beginning Wednesday and ending Saturday.
Saturday afternoon saw the start of mountain thunderstorms that
will continue for several more days. While the convection ended
before midnight...thunderstorms will resume just after noon this
Sunday. The thunderstorm activity resulted from a piece of energy
that broke off from a trough moving over the West Coast ridge
pattern and through western Canada on Friday/Saturday. Satellite
imagery is starting to show the circulation system off the
northwest California coast that will be dropping due south for the
next few days. As it moves south...a vorticity lobe extending toward
Nevada will provide enough dynamic lift to support convection over
the Sierra Nevada. Therefore...will keep the mention of
thunderstorms over the Sierra with a wider coverage area then
that seen on Saturday. In addition...will only expect the bulk of
the cloud cover over the mountains...with the San Joaquin Valley
remaining mostly clear today.
The piece of energy will continue moving south and is prognosticated to
form a Rex blocking pattern by Monday. This Rex block will then
slowly progress east with the upper low moving into Southern
California. The main affect to the forecast from this trajectory
is the coverage of the precipitation over central California during the
middle-week period. While the flow will allow for some moisture to
advect into the region along with weak difluent flow...mountain
and desert convection will still be supported. Convection over the
San Joaquin Valley may be a bit more difficult to obtain...but
will keep a mention for now.
On the other hand...models then introduce a deeper trough behind the
Rex block while increases the confidence of wide area showers and
thunderstorms on Wednesday. While uncertainty is starting to
increase by midweek...models still have a good handle on also
dropping the second low toward Southern California by Thursday. At
that point...convection and precipitation will begin diminishing with
precipitation now confined to the mountains. Friday shows yet another
trough passage that may occur by the end of the week. Will keep a
mention of precipitation for Friday and Saturday...but confine it to the
mountains based on the level of uncertainty.
thunderstorms possible over the Sierra Nevada north of Kern County
after 19z Sunday with areas of MVFR and isolated IFR in heavier
showers. Otherwise...VFR conditions can be expected throughout the
central California interior during the next 24 hours.
Air quality issues...
on Sunday April 19 2015...unhealthy for sensitive groups in
Fresno County. 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 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 04-19 93:2009 54:1967 64:1938 35:1955
kfat 04-20 96:2009 53:1957 62:1989 36:1896
kfat 04-21 98:2009 50:1900 64:2012 36:1968
Kbfl 04-19 98:1910 54:1967 62:1938 38:1996
kbfl 04-20 98:1906 59:2007 64:1939 36:1904
kbfl 04-21 99:2009 57:2010 64:2009 33:1904