Area forecast discussion 
National Weather Service San Francisco Bay area 
1037 am PDT Monday Sep 22 2014 


Synopsis...two more days of near normal temperatures and coastal 
low clouds in store for the forecast area. A Pacific storm system 
will bring rain to our area by midweek. 


&& 


Discussion...as of 09:15 am PDT Monday...made a few minor changes 
to the forecast this morning with respect to cloud cover based off 
the latest visible satellite. Should continue to see the stratus 
burn-off through the morning hours and give way to mostly sunny 
skies inland by this afternoon. Otherwise...the forecast looks on 
track for today and will work on the details of the midweek 
system set to bring rainfall to the region...especially across the 
North Bay southward to the Santa Cruz Mountains. 


&& 


Previous discussion...as of 3:00 am Monday...unlike the past several 
days the overnight satellite product is a bit different early this 
morning with plenty of breaks off the coast and clouds in the bays 
and adjacent valleys. Last few frames do show some filling in from 
the waters so will be interesting to see how things look by day 
break. Could actually see sunrise near local beaches -- especially 
for parts of Monterey County south of Point Sur. Temperatures will 
be similar to yesterday with highs in the 60s to middle 70s at the 
coast with middle 70s to lower 80s in most urban spots. Tuesday looks 
to be a near repeat of today with little change in the surface 
pattern and both 500 mb heights and 850 mb temperatures virtually 
unchanged. 


All attention continues to focus on Wednesday and Thursday as a 
Pacific storm system will advance to the pacnw first on Tuesday 
then down into the northern half of California. Rain will enter 
northern California early on Wednesday and then spread to the 
south through the day. Although there remains some disagreement 
between the speed and coverage of the rain, there is overall 
fairly good agreement that the associated cold front will advance 
to the North Bay Wednesday afternoon or evening and then continue 
to progress to the south and east during the overnight hours and 
into Thursday. Due to the rain and clouds temperatures will cool 
to below normal values inland by Thursday. 


The event is still a few days out, so unfortunately we still have 
a limited number of more detailed models for quantitative precipitation forecast although general 
indications are more than half an inch could fall by Thursday 
afternoon over the North Bay with closer to .1" - .25" around sf 
Bay as well as the Santa Cruz Mountains. Other spots including 
the Santa Clara Valley and Monterey will likely pick up less 
rainfall. Possible that higher amounts could occur with precipitable water 
amounts forecast to be as high as 1.65" Wednesday night. Models 
have also continued to indicate some instability aloft, so added 
a slight chance for thunderstorms as well especially over the 
northern waters and the North Bay. With noting that the overall 
trend over the past couple of days has been for a stronger and 
wetter system. 


There had been a large discrepancy between the model solutions 
for Thursday night into the weekend which thankfully seems to be 
resolved. Latest trends are now more in line with the operational 
European model (ecmwf) which has the longwave trough overhead for a much longer 
period as a ridge builds across the central Continental U.S.. this will 
allow US to keep at least a chance of showers going across part 
of our County Warning Area into the weekend along with temperatures generally 
cooler than normal (especially for inland spots). 


Looking into next week, quiet weather returns as the main storm 
track shifts up to the north. 


&& 


Aviation...as of 10:30 am PDT Monday...the marine layer remains 
around 2000 feet this morning. Northwest flow is scouring stratus 
from the Bay area while also driving it further into the Santa 
Clara Valley and Monterey peninsula. Expect clearing at all but 
mry before morning is out. VFR this afternoon with mostly light 
winds. Some patchy stratus to stay along the coast today and 
likely to return to the terminals tonight. 


Vicinity of ksfo...becoming VFR momentarily. Onshore winds to 
around 15 knots this afternoon. Stratus to return tonight late 
evening. 


Ksfo bridge approach...similar to ksfo. 


Monterey Bay area terminals...sns to clear in the next hour as 
ceilings erode in the Salinas valley. Northwest flow to maintain ceilings at mry 
into early afternoon. Then VFR through middle to late afternoon. 


&& 


Climate...autumn officially begins (autumnal equinox) at 7:29 PM 
PDT today. 


&& 


Marine...as of 09:15 am PDT Monday...light to moderate 
northwesterly winds will continue along the central coast as high 
pressure remains over the eastern Pacific. A cold front will will 
move through the region middle week bringing a chance for showers and 
possibly thunderstorms. In addition...northwest swell will build 
and impact our area starting on Wednesday. 


&& 


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


$$ 


Public forecast: rgass 
aviation/marine: ac 


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