Weather

526 
fxus66 kmtr 071118 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
418 am PDT sun Sep 7 2008 


Discussion...as of 3:10 am PDT Sunday...fog product imagery is indicate 
fog developing along the coast...especially during the last hour or 
so. The feet Ord profiler is indicate a weak marine layer of 400 feet. 


Temperatures this morning are several degrees cooler than yesterday... 
mainly in the 50s and 60s...with 70s and even a few lower 80s in the 
mountains. The gradient picture indicate a weak northerly gradient of 2.4 
mb between Arcata-sfo and a 1.9 mb onshore gradient between sfo-SAC. 
The onshore flow has helped increase dew points across the district... 
leading to the fog seen developing along the coast. With the shallow 
marine layer the fog could be locally dense this morning. 


Models are in agreement in dropping a weak trough south along the 
coast today and Monday. The flow will become more onshore...allowing 
significantly cooler air to move onto the coast and into the Bay. 
The GFS and nam12 bring cooler air through the Bay and into the North 
Bay valleys...which should be the first inland locale to experience 
significant cooling. The coast and bays should be much cooler today 
as well. As the trough deepens along the coast Monday and Tuesday all 
areas should be significantly cooler...with temperatures actually below 
normal with the cooler air aloft and onshore flow. Fog and low 
clouds will be widespread along the coast and into the coastal 
valleys during the night and morning hours. 


The flow looks to become more offshore the middle of next week as 
ridging builds into the Pacific northwest. This should bring warmer temperatures 
and less low clouds and fog. By the end of next week...and into 
next weekend medium range models are hinting at a cutoff low off the 
coast with a south flow aloft...however medium range models keep the 
airmass over central California dry. The 00z GFS ensembles indicate 
dry weather right through the middle of September. 


&& 


Aviation...as of 4:20 am PDT Saturday...current satellite fog 
product showing mostly clear skies around the San Francisco Bay 
area. A trough of low pressure is forecast to slide by the area 
today resulting in increased dewpoints and slightly cooler 
temperatures. This translates into a few low clouds around the San 
Francisco Bay area this morning. Expect VFR to prevail today with 
stratus finally returning late tonight. 


Monterey Bay area terminals...dew points are increasing around the 
area this morning as a precursor to the return of stratus to the 
Monterey Bay area...but at this point the satellite fog product is 
indicating mostly clear skies across the region. A trough of low 
pressure is forecast to skirt across northern California this will 
restore onshore flow and usher in stratus this evening. At this 
point anticipate patchy fog otherwise VFR through this afternoon and 
LIFR conditions late tonight. 


&& 




Mtr watches/warnings/advisories... 
... Bay. 


$$ 


Public forecast: mhs 
aviation/marine: Larry 




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