706 
fxus66 ksto 072300 
afdsto 


Area forecast discussion 
National Weather Service Sacramento California 
400 PM PDT Thursday Aug 7 2008 


Discussion... 
according to water vapor a dry slot is moving over northwest 
cal...encompassing all of our County Warning Area but the southeast corner. The more 
enhanced convection is within the moist area on the periphery of the 
dry slot...in southern Oregon and western Lassen Colorado eastward of the Burney 
Basin. There is a modest area of increased moisture moving over the 
northern half of our County Warning Area and this is what would likely fuel the slight 
chance of ts over northern Shasta Colorado this evening. The threat of showers 
and ts will diminish tonight as winds aloft will transition to a 
drier SW flow. Due to the strong Delta wind we have had gusty winds 
up to about 20 miles per hour through the Central Valley today and a steady 
sustained wind in the lower 20s at Travis AFB. As I mentioned in 
the update earlier today...typically the wind strength through the 
Strait is stronger from middle afternoon to near sunrise with the strongest 
winds during the early morning hours from midnight to just before 
sunrise. 


The next forecast concern is the strength of the Delta stratus push 
Friday and Sat mornings. The gradient is up 0.6 from yesterday to 4.3 
mb. Nam12 is showing that higher surface pressure will develop Friday 
night. So as the marine layer strengthens...the increased 
subsidence will squash down the stratus depth. Whether the 
stratus pushes into the valley depends on how strong the gradient is 
and the depth of the marine layer. Friday and Sat will see a cool down 
in the lower SAC valley and Delta with this increased flow. The 
trough finally pushes through the region late Sat into sun bringing 
a northerly flow to the northern portion of the County Warning Area at night and Sun 
night. Temperatures will rebound sun as a ridge moves over the region 
before SW flow takes over on Tuesday. 


Extended discussion (monday through thursday)...another trough of 
low pressure will dig off the coast next week...keeping dry 
southwesterly flow over northern California. There are some 
discrepancies with placement and strength of this low. At this 
time...the 12z GFS solution is slower than the European model (ecmwf) or the UKMET. 
However...think it may be trending better with keeping high pressure 
over the west a little longer. Therefore...expect a gradual warming 
trend through the middle of the week. 


&& 


Aviation...southwesterly flow aloft will strengthen over the next 
24 hours...as the upper level trough of low pressure approaches the 
coast. As a result...VFR conditions will prevail...except areas of 
MVFR in smoke near the vicinity of the fires. Cumulus build ups 
will continue to be possible over the higher terrain this 
afternoon...with an isolated shower or thunderstorm producing local 
MVFR conditions possible. Otherwise...expect a strong onshore 
gradient to develop Friday and Saturday...bringing gusty southwest 
winds up to 35 kts through the Delta and over the higher terrain. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$