042 
fxus66 kmtr 210555 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
955 PM PST Thursday Nov 20 2008 


Discussion...as of 8:30 PST PM Thursday...zonal flow resides over 
northern California at this time as a baggy trough exists southwest 
of Southern California. The flow through these two features has 
brought a few high clouds to the area today and will continue to 
keep high clouds in the sky over the next several days. A low 
pressure system in the Gulf of Alaska is producing multiple 
short wave troughs and sending them across the northern states. 
Eventually the baggy trough to our southwest will combine with one 
of these short waves from the northwest and help to dig the system 
south into central California. At the beginning of next week both the 
GFS and the European model (ecmwf) forecast a portion of this short wave energy to cut 
off from the main flow and strengthen offshore of central California. 
As with any cut-off low its movement is very difficult to forecast 
since by definition weak flow surrounds it. Therefore...the forecast 
will contain sight chance probability of precipitation from Monday afternoon through at least 
middle week. The timing of the precipitation will be refined once the 
disturbance develops and the amount of moisture it engulfs can be 
determined. 


&& 


Aviation...as of 9:55 PM PST Thursday...a few patches of low clouds 
remain at this hour none of which are affecting area terminals. 
Mainly clear skies will persist through Friday with a few high clouds 
streaming in from the west. West wind persist over the district as 
high pressure builds off the California coast and ridges across 
Oregon. Winds will shift offshore Friday as the high builds over the 
Great Basin and reverses the flow. Patchy fog may developing 
during the early morning hours Friday over inland valleys and along 
the coast as a result of lingering low level moisture. Clearing is 
expected between 14z-17z. 




Terminal Aerodrome forecast (tafs) format change... 


As of 0000z (november 5 2008) the National Weather Service in agreement with the FAA has 
changed the taf format to conform to international standards outlined 
in icao annex 3. The change includes the initiating of 30-hour tafs 
for high impact U.S. Airports. To accommodate the extended taf 
period...the format of all tafs have changed. The change involves 
identifying the data associated with each time group. 


Ksfo and koak are now 30-hour tafs. 


For additional information regarding the change please visit the 
aviation weather centers website: 


Http://aviationweather.NOAA.Gov/notice/taf30.Php 


&& 


Mtr watches/warnings/advisories... 
tonight...Small Craft Advisory all coastal waters out to 60 nm...except bays. 


&& 


$$ 


Public forecast: Evans 
aviation/marine: CW 


National Weather Service on the web at weather.Gov/sanfrancisco