Scientific Forecaster Discussion

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

Synopsis...
lots of high clouds across central California today as a weak
weather system will passes through. There will be a chance for
showers in the Sierra and even a few thunderstorms look possible. A
few more showers are possible Saturday over the Sierra then quiet by
Sunday. Temperatures will remain warm through the weekend and into
Monday. However...a more vigorous Spring system will arrive Tuesday
ushering in much cooler...below normal...temperatures and the
potential for light rain and snow in the Sierra. 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...
temperatures remain quite mild early this morning with most of the
San Joaquin Valley and desert areas of eastern Kern County sitting
in the 60s while nearby foothills bask in the 50s. This is all
thanks to the trapping of long wave radiation by the thick shield
of cirrus clouds overhead associated with a low passing to our
south. This low...and another decaying frontal band arriving from
the north...are pushing moisture levels to 100-200 percent of
normal values...depending if you/re looking at radiosonde observation climatology or
satellite derived precipitable water data.

No significant errors in model init fields noted to cause great
concern with the forecast this morning. First concern is
convective potential over the Sierra this afternoon and early
evening. Of course elevated moisture levels coupled with above
average boundary layer temperatures raises the concern of mountain
convection. NAM bufr sounding for Sierra Point c01 shows about 400
j/kg of cape developing this afternoon. The profile is rather
tall/skinny suggesting updrafts will not be exceptionally strong
and lfcs generally hang at the -30c level...another indication
that lightning/thunderstorm activity will not be exceptionally
robust. NAM MUCAPE fields depict afternoon maximum values ranging
from 500-700 j/kg...on the order of what we saw last week. Sref
calibrated thunderstorm parameter /courtesy Storm Prediction Center/ show over a 70
percent chance of ts along the Sierra around 21z-00z today. Latest
hrrr runs are also convecting along the Sierra beginning around
18z with even some activity down into the Frazier Park area. Fwiw
Storm Prediction Center also has the Sierra in a general thunder for today. All this
adds up to a significant boost in chances of seeing a meas Ely 0.01
inches of precipitation in the mountains today. Thinking most of
the activity will be constrained to elevations 6-8kft and higher.
Corfidi vectors and winds in the cloud-bearing layer will be about
10kt from the southwest so what does form will likely drift into
the Owens Valley.

All the parameters mentioned above basically hang around into
tomorrow though all lower in intensity. Increased probability of precipitation though with
idea of more showers developing but held off on thunder for now
due to convective parameters not being as robust. Should see much
less activity...maybe just enhanced clouds...Sunday as short wave
ridging builds in. Something we/ll keep in mind is that with the
very warm temperatures the past few weeks there has been a
flourish of activity in the Sierra with more higher-elevation
roads opening...more hikers about...etc.

Next trough will approach Monday. GFS/ec ensembles are getting
fairly locked into the timing and amplitude of this one...keeping
it open as it traverses California. GFS modtrend depicts a pattern
suggestive of a slowing in forward progression. So we/ll likely
see a spike in temperatures Monday afternoon...850 mb temperatures will
reach around 16c pushing peak surface values in the valley/desert
areas into the upper 80s and into the 70s for the foothills. We/ll
start to see winds increase over the Sierra and eastern Kern
County Monday afternoon. By Tuesday the base of the trough cuts
right through our County Warning Area. Really not much moisture with
it...isentropic analysis doesn/T look really great as the front
moves through...so even though snow levels are dropping down to
near 5000ft not much precipitation is expected. More notable changes will
be strong winds over the mountains and through central/eastern
Kern County. Will likely see at least a Wind Advisory for the
Sierra and eastern Kern County with this system...highlighted by
severe weather potential statement currently...late Monday into Tuesday. We also included
blowing dust in the desert areas Tuesday afternoon. Lower level
temperatures are scheduled to drop around 10c which will put maximum
temperatures actually below normal for a change.

Ridging is anticipated Thursday and Friday for a gradual return to
more quiet and warm weather.

&&

Aviation...
mountain obscuration in snow showers after 18z Friday. Isolated
thunderstorms also possible along the Sierra. Otherwise VFR
conditions will prevail across the central California interior during the
next 24 hours.

&&

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...iniguez
AVN/fw...iniguez
synopsis...iniguez

Weather.Gov/Hanford