Area forecast discussion 
National Weather Service San Francisco Bay area 
636 PM PST Tuesday Mar 3 2015 


Synopsis...a building ridge of high pressure along the West 
Coast will result in dry weather conditions and a slight warming 
trend through the upcoming weekend. 


&& 


Discussion...as of 02:24 PM PST Tuesday...a middle/upper level ridge 
off of the West Coast will slowly strengthen and build inland 
through late week as the long-wave trough axis over Southern 
California shifts eastward. As a result...850 mb temperatures are 
forecast to warm above 10 degrees c and bring surface temperatures 
into the 70s for most locations by Thursday. These warm and dry 
conditions are then forecast to persist through the upcoming 
weekend and likely into early next week as the ridge remains 
parked over much of the region. With weak offshore flow possible 
over inland areas this weekend...a few spots may even reach or 
exceed the 80 degree mark. With limited moisture in the boundary 
layer...do not expect much in the way of stratus during the late 
night/early morning hours through early next week. 


The medium/long range models continue to show the middle/upper level 
ridge shifting eastward and weakening by the middle of next week. 
This pattern change would allow for an upper level trough to impact 
the Pacific northwest and bring widespread rainfall to the San 
Francisco/Monterey Bay region Wednesday into Thursday of next week. 
Temperatures will also cool over the region during the latter half 
of next week as a result. Will continue to monitor this possible 
pattern change for next week...stay tuned. 


&& 


Aviation...as of 6:20 PM PST Tuesday...the California coastal trough will 
very likely shift just offshore by early Wednesday morning. Local 
onshore winds this evening will trend to neutral or briefly weak 
offshore during this time. The larger scale wmc-sfo gradient 
increases modestly to approx 8 mb by Wednesday morning per today's 
and last evening's NAM model runs. This favors VFR for the Bay 
area terminals for the period. 


Am less certain about the low cloud cover in the Monterey Bay area 
for tonight as partial low cloud cover is converging on this area 
as of this writing. The WRF model run shows an eddy circulation 
developing over the Bay waters by midnight with a trend toward southeast 
winds developing over the northern Salinas valley very early 
Wednesday morning. As a result of this southeast wind the low clouds will 
likely move out over the waters Wednesday morning. Also a southeast wind 
flow is consistent with what we usually see in offshore patterns 
even if they are only brief...and it is expected to be brief. 


Weak to locally moderate onshore winds return all areas by Wednesday 
afternoon as the NAM shows the trough moving back inland...but we 
could see a similar pattern of brief offshore wind developing once 
again very late Wednesday night into Thursday morning. 


On a side note: coastal buoy water temperatures have cooled off a little 
more in the last 1 to 2 weeks presently ranging in the middle to upper 
50s north to south...still a little above normal but cooler. We may 
be seeing more in the way of coastal low clouds and/or fog through 
this week with possible weather related implications for area terminals 
due to this cooling and further strengthening of the upper level 
ridge. 


Vicinity of ksfo...VFR. Onshore winds less than 20 knots will 
continue to subside by later this evening. Light and variable wind 
trends toward light NE wind Wednesday morning. Westerly winds return 
by middle to late Wednesday afternoon. Moderate to high confidence. 


Ksfo bridge approach...similar to ksfo. 


Monterey Bay area terminals...may need to amend the 00z kmry and 
ksns tafs to include more low cloud cover tonight/Wednesday morning. 
Low confidence forecast overall especially with clearing times 
Wednesday morning. Cloud cover as well as clearing will be highly 
dependent upon strength of the eddy circulation if it even develops 
overnight. Much improved chances for VFR during the day Wednesday 
but low clouds may not be that far away from the terminals this 
time tomorrow evening. 


&& 


Marine...as of 02:24 PM PST Tuesday...high pressure situated off 
the West Coast will maintain northerly winds along the central 
coast. Locally gusty winds will be possible north of Point 
Reyes...especially the outer waters. Seas are expected to be 
moderate and gradually decrease through the week. 


&& 


Mtr watches/warnings/advisories... 
... Arena to pt Reyes 10-60 nm until 3 am 


&& 


$$ 


Public forecast: rgass 
aviation: canepa 
marine: mm 


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