Area forecast discussion 
National Weather Service San Francisco Bay area 
1020 PM PDT Friday may 22 2015 


Synopsis...low pressure will gradually exit the area to the east 
over the next few days...resulting in a slight warming trend this 
weekend. Patchy drizzle is possible in coastal areas late tonight 
and Sunday morning...especially south of San Francisco. 
Otherwise...dry weather is forecast through the weekend and well 
into next week. 


&& 


Discussion...as of 8:50 PM PDT Friday...an upper trough moving to 
the east of California produced considerable thunderstorm 
activity over Nevada and eastern California today. The low was too 
far east to generate anything more than a few afternoon cumulus 
build-ups over our area. 


The longwave trough position will continue to shift eastward over 
the next few days. However...a shortwave trough is forecast to 
traverse California from northwest to southeast on Saturday...triggering another round 
of convection over the Sierra Nevada...and perhaps as close to our 
forecast area as Lake County. Considerable low level moisture 
remains across our area...and as the shortwave approaches from the 
northwest later tonight...it may enhance onshore flow enough to 
produce areas of drizzle in coastal areas late tonight and 
Saturday morning...particularly in coastal areas south of the 
Golden Gate. 


The general trend over the weekend will be for gradual warming and 
more widespread clearing as the longwave trough continues to move 
to the east and an upper ridge over the eastern Pacific edges closer 
to the West Coast. Temperatures should climb to near normal by Sunday. 


The warming trend will probably stall on Monday and Tuesday as an 
upper low settles into the Pacific northwest and temporarily weakens the 
ridge. Warming is then likely to resume during the second half of 
next week when the models agree that the upper ridge will re-build 
along the West Coast. But temperatures are not expected to warm 
more than a few degrees above normal...and relatively cool 
conditions will persist near the coast due to continued onshore 
flow. 


&& 


Aviation...as of 10:07 PM PDT Friday...not much change from the 
previous discussion. VFR/MVFR ceilings continue this evening with a 
mix of cloud layers around the region. Low level moisture will 
linger into tonight with a few patches of drizzle becoming 
possible very late at night. An upper level high over the epac 
will slowly edge in from the west during the period. Subsidence 
associated with the high will result in a gradual warming within 
the lower levels causing the marine layer inversion to become re- 
established over the Holiday weekend. By late Sunday night into 
Monday 850 mb level temperatures are predicted to reach near 15c. 


Vicinity of ksfo...MVFR ceilings. Gusty westerly winds are likely to 
return on Saturday. 


Ksfo bridge approach...similar to ksfo. 


Monterey Bay area terminals...VFR/MVFR gradually decreasing to IFR 
very late. Patchy drizzle possible late. Clearing returns by late 
Sat morning. 


&& 


Marine...as of 10:02 PM PDT Friday...high pressure is strengthening 
over the coastal waters in the wake of a sluggish upper low. This 
pattern is leading to generally deteriorating conditions from 
increasing northwest winds and building seas. Unfavorable winds 
and seas are forecast persist through the weekend before beginning 
to taper off early next week. 


Overall forecast looks good. Minor adjustments made to the forecast 
winds for the San Francisco Bay waters north of the Bay Bridge 
Saturday afternoon and evening....decided to add a Small Craft 
Advisory. Bumped up forecast winds a little for Sunday...but may 
not be enough. Later shifts may need to consider adding a Small 
Craft Advisory in for later Sunday. 


&& 


Mtr watches/warnings/advisories... 
... Arena to pt Reyes 10-60 nm 
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm 
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm 
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm 


&& 


$$ 


Public forecast: dykema 
aviation: canepa 
marine: drp 


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