Area forecast discussion 
National Weather Service San Francisco Bay area 
858 PM PST Tuesday Dec 1 2015 

Synopsis...warming temperatures through Wednesday. Next cold 
front arrives Thursday morning in the North Bay. Breezy winds and 
precipitation will be focused over the greater San Francisco Bay 
area with lesser amounts over the Monterey Bay area on Thursday. 
Seasonal temperatures on Friday and Saturday. Weak system brushes 
the North Bay on Sunday. 

&& of 8:58 PM PST short term concerns 
with no forecast updates planned for this evening. Compared to 
previous nights readings are running fairly mild in the 40s to 
around 50 but will continue to drop overnight despite some middle and 
high clouds as a system passes to our north. 

A nice Wednesday on tap with warm southerly breezes along with 
some high cloudiness at times. 

Forecast focus remains on the Thursday system. 00z NAM is in line 
with the 18z and not overly impressive. Rain moves into the North 
Bay by Thursday morning then quickly marches southeastward 
through midday. Latest solutions of the NAM showing only light 
rain for the South Bay and Monterey Bay region. The 00z GFS 
solution is wetter and more in line with the latest Canadian and 
European model (ecmwf) runs. So for the moment the NAM is the drier outlier. 
Looking out near 40n/150w the center of the incoming circulation 
has a lot of cold air associated with it but the brunt will miss 
US to the north. Looking at modeled winds up at 300 mb shows the 
incoming jet streak quickly falling apart as it moves into 
northern California and the Sierra on Thursday. Must say that 
moisture plume shouldn't be a problem with latest AMSU scans and 
modeled tpw of both the NAM and GFS bringing a tongue of 1 inch 
tpw to our door step Thursday. Anyway thats all of the latest 
trends...will see what the Euro shows overnight. Still looks on 
track for 0... in the North Bay on Thursday with 
the biggest impacts for the midday and afternoon commutes. So far 
this year these cold core storms have in general over-delivered so 
will see if that trend continues. In fact the North Bay is 
currently showing some of the lowest year to date rain trends with 
Santa Rosa at only 23% and the city at 32%. So will see if we can 
put a little Dent in those numbers by Thursday evening. 

Looking ahead the pattern over the northern Pacific is actually 
quite active. Still a chance of some North Bay showers later 
Sunday and again Monday as system mainly impact Washington and 
Oregon. However the just received 00z GFS shows potentially 
significant system by about next Thursday which has been 
consistent and supported by the European model (ecmwf) with hints of a secondary 
system and plunge of colder air by weekend of the 11th. 

El Nino type storms still not expected until later in January or 
February. Current state of mjo looks like its about to wither 
with the pna teleconnection trending negative by later next week 
the best long term tool for supporting continued active pattern 
across the west. 


Previous of 3:00 PM PST Tuesday... satellite imagery shows 
a weak upper disturbance offshore of extreme northwestern 
California and the Pacific northwest early this afternoon. This 
disturbance is streaming middle to high level clouds into California 
from the north and will continue to result in increasing clouds 
into the evening. Rainfall from this system will remain north of 
our forecast area. 

Temperatures have warmed 4 to 10 degrees over yesterdays readings 
and temperatures will peak near normal seasonal values this afternoon. 
The warming trend will continue into tomorrow when we are forecast 
to be a few degrees above normal through the day. This warming 
trend comes as a short lived ridge develops over the state. 

Weather models show a much more progressive synoptic scale 
flow now that the Rex block that brought US several days of 
subfreezing temperatures has been ejected from the intermountain 
west. Models continue to converge on a Thursday morning arrival 
for the next storm system. This storm system is projected to be 
the strongest system of the last few that have brushed through 
the area but will not be more impressive than a typical system for 
this time of the year. The latest model runs all show that the 
bulk of this systems energy and moisture will sweep through the 
northern half of our forecast area and northward. There is some 
model uncertainty over how far southward the base of the trough 
will progress on Thursday... with the GFS slightly more energetic 
and pushing southward into the Big Sur region. The surface frontal 
band will push further south into the Monterey Bay region but 
will weaken steadily as it propagates southeastward away from the 
upper support. Amounts in the North Bay will range from 1/3" to 1" 
or more meanwhile the Monterey Bay region may see as little as a 
several hundredths to a few tenths. Latest model runs continue to 
trend drier for the southern half of the County Warning Area... especially for 
Monterey and San Benito counties. Onshore winds will become breezy 
inland by Thursday afternoon and taper off overnight. Showers 
linger into Thursday night. 

Near normal temperatures for Friday and Saturday as a weak ridge develops 
in wake of aforementioned storm system. 

For Sunday... long term models continue to show a weak trough 
approaching the coast. Models continue to trend this system 
weaker and weaker each run but light precipitation looks possible 
for the North Bay and posbl into immediate Bay area before 
fizzling as it moves onshore. 

A deeper moisture tap may be in store for late next week. Stay 

&& of 3:30 PM PST Tuesday...airmass has dried out in 
the lower levels. VFR through the period with mainly high clouds 
and light winds. 

Vicinity of ksfo...VFR. 

Ksfo bridge approach...similar to ksfo. 

Monterey Bay area terminals...VFR. 

&& of 08:39 PM PST Tuesday...winds will gradually 
increase over the coastal waters the next day or so as a storm 
system approaches the region. A storm system will swing through 
the region Wednesday night into Thursday bringing gusty 
winds...periods of rain and rougher seas. A moderate period swell 
will continue to decrease through mid-week...but a larger swell is 
still on track for late in the week. 


Mtr watches/warnings/advisories... 



Public forecast: rww 
aviation: west pi 
marine: west pi 

Visit US at www.Weather.Gov/sanfrancisco 

Follow US on facebook and twitter at: 

National Weather Service Glossary of Abbreviations
Back to forecast page
Non-Expanded Version (with abbreviations)

Units: English | Metric

Find the Weather for any City, State or Zipcode, or Country:

U.S. State List | Severe Weather | Tropical Storms | Ski Conditions
United States | Canada | Central America | South America | Asia | Europe | Australia | Africa | Islands

Weather Underground

Copyright© 2015
The Weather Channel, LLC