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fxus66 khnx 180855 
afdhnx 


Area forecast discussion 
National Weather Service San Joaquin Valley - Hanford California 
155 am PDT Thursday Mar 18 2010 


Synopsis... 
a ridge of high pressure along with above normal temperatures and 
dry conditions will prevail through the week...except there is a 
slight chance of thunderstorms and snow showers this afternoon and 
evening over the Sierra Nevada. 


&& 


Discussion... 
a weak upper-level trough is moving into the Pacific northwest this 
morning. This trough brought some high clouds to the region Wednesday 
and will bring slightly cooler temperatures to the region. Although 
the trough is not expected to bring any precipitation to the central 
and southern San Joaquin Valley...it may bring some afternoon showers 
and thunderstorms to the southern Sierra Nevada. 


The 00z NAM-12 forecasts surface-computed convective available potential energy of up to 1600 j/kg 
over the southern Sierra Nevada at 21z this afternoon...increasing to 
2000 j/kg over Kings Canyon by 00z Friday. At 21z...surface-computed 
lifted indexes over the southern Sierra Nevada are negative...with a 
-6 over northern Tulare County. Three hours later...areas of -6 are 
forecast from Kings Canyon north to Yosemite National Park. The peak 
850-mb Theta-E over the southern Sierra Nevada this afternoon is 
about 333 k...and 500-mb temperatures over the central California 
interior are forecast to be -16 to -18 c...so severe thunderstorms 
are not expected. The 300-mb jet is forecast to move over northern 
California this afternoon...and stay well north of the Hanford 
warning/forecast area. Storm Prediction Center has the southern Sierra Nevada under a 
general risk of thunderstorms today...so have increased probability of precipitation over 
the southern Sierra Nevada slightly. Based on the 00z NAM-12 
convective parameters...could see a heavy thunderstorm or two... 
but most thunderstorms will be in the moderate range. 


The upper-level trough axis drops south of the Hanford warning/ 
forecast area tonight...as the next upper-level ridge builds along 
the coast. Meanwhile...the next trough is digging roughly along 
147 west. This trough will push the ridge onshore Friday and 
Saturday...with the ridge axis over the central California interior 
Saturday afternoon. 


The upper-level trough moves into the Pacific northwest Sunday 
afternoon/evening. The trough flattens the ridge...the a low in the 
base of the trough begins to close off. The main trough drops into 
the northern Great Basin by 12z Monday...while the low in base of 
the trough drops south and into Baja California California by 18z Tuesday. As 
the trough drops south...it may bring enough dynamics to trigger a 
few showers over the high country of the southern Sierra Nevada 
Monday night and Tuesday. The trough will also bring a push of cold 
air into the central California interior...with the medium-range 
models forecasting 850-mb temperatures to fall as much as 4 c over 
parts of the Hanford warning/forecast area. This will cool 
temperatures to near normal after a string of above-normal 
temperatures that will run through the weekend into next Monday. 


The models are in some disagreement for next Wednesday. The 00z GFS 
has another ridge over the coast...while the European model (ecmwf) brings a 
short-wave into the Pacific northwest for a more zonal flow over 
California. Have opted for persistence temperatures for day 7 at 
this time...but have gone dry for all areas. 


Note...Spring begins at 1732z /1032 PDT/ on March 20th. 
Although Spring does not begin until the 20th...both Fresno 
and Bakersfield already have had their days with approximately 
12 hours of daylight and night...on the 16th and 17th. This is 
due to the fact that the Earth is not exactly spherical and to 
atmospheric refraction at sunrise and sunset. 


&& 


Aviation... 
local MVFR visibilities in mist over the San Joaquin Valley through 
18z Thursday. Areas of MVFR and local IFR conditions in showers and 
thunderstorms over the southern Sierra Nevada between 18z Thursday 
and 06z Friday. Otherwise...VFR conditions will prevail across the 
central California interior through 12z Friday. 


&& 


Air quality issues... 
none. 


&& 


Hnx watches/warnings/advisories... 
none. 


&& 


$$ 


Public...Sanger 
AVN/fw...dch 
synopsis...tlm 


Weather.Gov/Hanford