143 
fxus66 kmtr 201215 
afdmtr 


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


Discussion...as of 4:15 am PST Thursday...the marine layer has 
become diffuse this morning as cooler air aloft is settling into the 
area. This is in response to a frontal system that is approaching 
northern California. As a result only areas of low clouds are 
being reported around the district but these clouds will become 
more widespread during the early morning hours. Frontal system is 
forecast to arrive in the early afternoon. There is a slight 
chance of rain for the North Bay counties from late morning through 
the afternoon. Low clouds will likely stay through the morning 
then get cleared out as the front passes. It will be another cool 
day today. 


Clearing will take place tonight as surface high pressure builds 
into Oregon and northern California producing a light offshore flow. 
If there is any rainfall in the North Bay there may be a patch or 
two of fog. The weekend will be dry and a little warmer as the next 
storm system passes north of the district. Longer range models 
are still bringing in an upper low to the central and Southern 
California coast Tuesday or Wednesday. The GFS brings the low into 
central California which would bring a slight chance of showers in 
the climatologically favored areas around the district Monday and a 
better chance Tuesday and Wednesday. The European model (ecmwf) brings the low into 
Southern California and there would be less chances in the northern 
part of the district. 




&& 


Aviation...as of 4:15 am PST Thursday...most of the high clouds 
associated with the passing trough are quickly moving out of the 
area. However...there still exists areas of low clouds around the 
district. Most of the IFR ceilings from yesterday and last night have 
lifted to MVFR and have been wobbling back and forth from scattered to 
broken. This trend will continue this morning with ceilings lifting and 
scattering out. Should see skies clear out fairly well this 
afternoon as cool dry air will mix down into the boundary layer on 
the back side of the exiting trough. 




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...none. 


&& 


$$ 


Public forecast: west pi 
aviation/marine: tentinger 


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