Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Joaquin Valley - Hanford California
455 PM PDT Friday Apr 18 2014

Update...
&&

Synopsis...
a weak storm system moving across the state will continue the
chance for showers and thunderstorms over the Sierra Nevada into
Sunday. Easter Sunday and Monday will be dry as high pressure
briefly builds over central California. Monday. However...a more
vigorous storm system will arrive Tuesday ushering in much
cooler...below normal...temperatures and the potential for light
rain and snow over the Sierra Nevada. Strong winds will
also be possible in the mountains and passes Tuesday with blowing
dust possible across eastern Kern County. Quieter and warming
weather will return later next week.

&&

Discussion...
at 2345z /1645 PDT/...thunderstorms continued to develop over the
southern Sierra Nevada...extending south from Yosemite National
Park south to the Tulare/Kern County line. National Weather
Service Doppler radar indicated that these storms could produce
hail up to half inch in diameter. Both radar and law enforcement
indicate isolated heavy rain rates although no flooding had been
reported at this time.

Lightning data showed in-cloud and cloud-to-cloud lightning
spreading westward over the Tulare County foothills...and debris
clouds likely will spread into the east side of the San Joaquin
Valley. Lightning also have developed over the piutes and along
the south flank of the Sierra Nevada near Cache creek.

Have updated the forecast to expand the thunderstorms across the
Kern County mountains and deserts this evening and increased cloud
cover over the east side and south end of the San Joaquin Valley.

&&

Aviation...
mountain obscurations over the Sierra Nevada in showers and
thunderstorms through 00z Sunday. Otherwise VFR conditions will
prevail across the central California interior during the next 24 hours.

&&

Previous disc... /issued 255 PM PDT Friday Apr 18 2014/

Discussion...
at 2150z /1450 PDT/...lightning data and National Weather Service Doppler radar detected
thunderstorms developing over the southern Sierra Nevada in Fresno
and Tulare counties...with the strongest storms over southern
Tulare County. In-cloud and cloud-to-cloud lightning was detected
over the Tulare foothills by both the lightning network and the
AWOS at the Porterville Municipal Airport /kptv/. An upper-level
low was located west of northern Baja California California and was producing a
southeasterly flow aloft over the Sierra Nevada. This flow will push
thunderstorm development northward and westward. Radar also shows a
few cells beginning developing over the southwest corner of Mono
County...moving into Mariposa County at this time.

Unstable conditions will continue over the southern Sierra Nevada
through this evening...and while thunderstorms likely will diminish
after sunset as the air cools and begins to stabilize...expect a few
showers to continue near the crest past midnight as the low moves
east and the flow aloft turns more easterly and generates orographic
lift over the eastern slopes of the Sierra Nevada.

In contrast to Thursday/S dry 18z NAM...today/S 18z run now has a
quantitative precipitation forecast of 0.13 inch for Yosemite Valley...twice the quantitative precipitation forecast of the 12z GFS
and 14z rfc guidance...and three times the quantitative precipitation forecast of the 12z WRF.

On the San Joaquin Valley floor...winds over western Merced County
have diminished as the upper-level trough moves inland and the
marine layer shrinks. At 1934z /1234 PDT/...the marine layer had
fallen to a depth of around 2500 feet at Fort Ord and marine air had
stopped spilling through Pacheco Pass.

The trough is forecast to move into the Great Basin overnight and
into Utah and Arizona Saturday. As the flow aloft turns northwest...
could see some showers and possibly a few thunderstorms develop over
the high country Saturday afternoon with lifting over the western
slopes of the Sierra Nevada.

An upper-level ridge is forecast to build into California Sunday and
persist into Monday...bringing a warming trend back to the region.
Warming will be strongest Monday ahead of the next storm system.

The global-composite water-vapor loop shows the next upper-level low
to be near 44n/145w this afternoon...west of Oregon. This storm will
reach California late Monday night...with snow showers along the
crest near Yosemite National Park by daybreak Tuesday and
precipitation spreading southward across the County warning forecast area Tuesday morning.

The medium-range models are in good agreement with a sharp drop in
850-mb temperatures over Fresno Tuesday morning...falling from
around 15 c at 00z Tuesday /1700 PDT Monday/ to around 4.5 c by 18z
/1100 PDT/ Tuesday...and to 3-4 c by 12z /0500 PDT/ Wednesday
morning. The snow level will fall from around 4500 feet near
Yosemite to around 5500 feet at Kings Canyon and to around 6500
feet in the Tehachapi Mountains. No snow is expected on the passes
between the San Joaquin Valley and the Southland through the
Tehachapi Mountains.

The cold airmass also will bring an abrupt cooling to central
California...with central and southern San Joaquin Valley highs
dropping from the middle 80s to around 90 Monday to the upper 60s to
lower 70s Tuesday and Wednesday.

The 12z European model (ecmwf) has a storm total quantitative precipitation forecast of up to a half inch over the
southern Sierra Nevada from this storm. The 12z GFS has a more
northerly storm track...with the heaviest precipitation north of the
weather forecast office Hanford County warning/forecast area. The highest quantitative precipitation forecast over the
southern Sierra Nevada from the GFS is only around a tenth of an
inch.

The main impact of this storm will be gusty winds over the west side
of the San Joaquin Valley and across the mountains and deserts of
Kern County as the cold front pushes through. Depending on how much
rain falls ahead of the front...blowing dust could be a concern.

Another ridge is forecast to build into California for next
Thursday...bringing another round of dry and warmer weather. High
temperatures next Thursday are forecast to recover to near normal.
Central and southern San Joaquin Valley highs next Friday are
forecast to warm into the upper 70s to middle 80s...a few degrees above
the normal for late April.

&&

Air quality issues...
none.

&&

Certainty...

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

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.

&&

Climate...
records
site date hi_max:year lo_max:year hi_min:year lo_min:year

Kfat 04-18 95:1910 51:1955 62:1939 36:1941
kfat 04-19 93:2009 54:1967 64:1938 35:1955
kfat 04-20 96:2009 53:1957 62:1989 36:1896

Kbfl 04-18 98:1910 55:1923 63:1954 35:1922
kbfl 04-19 98:1910 54:1967 62:1938 38:1996
kbfl 04-20 98:1906 59:2007 64:1939 36:1904

&&

Hnx watches/warnings/advisories...
none.

&&

$$

Public...Sanger
AVN/fw...Mendenhall
previous discussion...Sanger
synopsis...Mendenhall

Weather.Gov/Hanford