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Area forecast discussion 
National Weather Service Sacramento California 
200 PM PDT Friday Jul 4 2008 


Discussion... 
a nice cool Fourth of July day for the region with temperatures 
below normal for this time of year thanks to the trough of low 
pressure that moved through the region. Winds through the Delta 
should continue overnight to be fairly moderate in strength...but in 
the absence of the trough of low pressure tonight impacting the 
interior the winds will be lighter tonight. This should translate 
into some wind this evening but generally around 10 miles per hour or less by 
the time the major firework shows get started. This should help to 
disperse some of the smoke given off from the displays. 


Another low pressure area moving into the Pacific northwest on 
Saturday will help to keep decent flow through the Delta 
overnight. 850 mb temperatures warm over todays values by several 
degrees so some decent warming is expected over today...but only 
to around normal for this time of year. Continued warming is 
expected for Sunday with a few of the warmest locations topping 
out around 100 degrees. 


A big change in the weather pattern will take place by Monday and 
continue for most of next week. High pressure will build inland from 
the eastern Pacific and north and westward from the Desert 
Southwest. This will bring much warmer and hot weather to the 
interior region. Reduced mixing due to the high overhead will lead 
to more stagnant conditions as smoke from wildfires becomes trapped 
in the boundary layer below the subsidence inversion. This may 
eventually lead to localized cooling if smoke layers become thick 
enough...similar to what happened last week. Tuesday and Wednesday 
of next week some isolated thunderstorms may develop over the crest 
south of Lake Tahoe. 


The heat looks to peak either Wednesday or Thursday of this coming 
week. The models differ in the extended period with the GFS keeping 
the ridge over the region longer while a couple of other models are 
indicating a weak shortwave moving through the Pacific northwest 
that would help to knock down the temperatures a few degrees on 
Thursday. If the GFS works out as the solution besides the extended 
period of heat it is also indicating a monsoonal surge of moisture 
moving over the interior late Thursday and Friday of next week. 
Beyond next Friday the models are in agreement with cyclonic flow 
developing over the region and cooling temperatures off for next 
weekend. 


&& 


Aviation... 
general VFR conditions are currently across interior northern 
California this afternoon with scattered clouds in the mountains. 
There are areas of MVFR and local IFR in the vicinity of fires. 
Southwesterly winds gusting around 25 knots in the Sierra are directing 
smoke away from the valley toward and over the crest. A shift to 
light northeast winds will push some smoke towards the Central 
Valley tomorrow morning. Low clouds may reach the western side of 
the Sacramento Delta Saturday morning but are not expected to extend 
as far in as they did today...so should not impact the Sacramento 
area. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$