Area forecast discussion 
National Weather Service San Francisco Bay area 
1032 PM PDT Tuesday Jul 29 2014 

Update as of 8:55 PM PDT Tuesday...based on combination of 
recently developing altocumulus castellanus over the North Bay evident in area 
webcams and latest visible and infrared satellite imagery...approaching tail 
end of weak upper level disturbance moving to the north-northeast approx 170 
miles west of the Golden Gate...and analysis of elevated 
convective parameters and model output soundings from just rec'd 
new 00z run of the updating the forecasts to add in a 
slight chance of dry thunderstorms north of the Golden Gate for 
the 9-hour period 06z tonight through 15z Wednesday. Everything from 
details of timing to exact boundaries of area at potential risk 
are intrinsically fuzzy given that the models have been doing a 
poor job lately with both initialization and forecasts of 
evolution of subtropical moisture plumes moving through our 
district. But want to get the message out that believe there is 
some risk and this is best current estimate of timing and area of 

Will also need to keep an eye on far southeast portion of our County Warning 
primary stream of moisture detraining from the remnant low of 
former Tropical Storm Hernan is now clipping through southeast Monterey 
County...and has thus shifted a bit farther northward than models 
were predicting. 


Synopsis...monsoon/subtropical moisture will continue to filter 
in over the forecast area tonight and tomorrow. This will result 
in partly cloudy skies and a relatively warm night due to extra 
humidity in the air. The airmass will begin to dry tomorrow 
evening so expect slightly cooler less humid nights. Otherwise...dry 
conditions and near normal temperatures can be expected through 
the remainder of the week. 


Previous of 2:26 PM PDT Tuesday...mostly clear skies are 
present over the forecast area this afternoon with stratus 
apparent over the coastal waters. The current satellite water 
vapour image is showing moisture streaming into Southern 
California and portions of our forecast area. Satellite blended 
total precipitable water is showing values 1.0 to 1.25 inches 
around the central California which is about 110 to 120 percent of 
normal. This moisture will primarily result partly cloudy skies 
and a warm humid night tonight. 

The 1200z European model (ecmwf) and gfs40 have initialized well with the current 
synoptic pattern. Both forecast models begin to move the 
monsoon/subtropical moisture out of the forecast area Wednesday. 
This will result in clearing skies and lower humidity 
values...slightly cooler evening temperatures. Otherwise looks 
like relatively mild weather through the beginning of next week 
with near normal temperatures expected. 

&& of 10:30 PM PDT Tuesday...the marine layer remains 
compressed at around 1000 feet and the onshore gradient mild. 
Stratus has begun to work its way into the bays this evening 
however the inland push will be limited by the shallow marine 
layer depth. 

Vicinity of ksfo...VFR through tomorrow afternoon. Stratus not 
expected to impact the terminal overnight. 

Ksfo bridge approach...patchy ceilings tomorrow morning could briefly 
impact approach early. Otherwise similar to ksfo. 

Monterey Bay area terminals...stratus now in mry and forecast to 
reach sns within the next couple of hours. Ceilings to burn off early 
tomorrow due to shallow marine layer. 

&& of 02:14 PM PDT Tuesday...northerly winds will 
prevail over the coastal waters. Moderate to locally strong 
northerly winds will be possible north of Point Reyes tonight and 
Wednesday. Seas will generally be gentle through the remainder of 
the week. 


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



Public forecast: blier/Larry 
aviation: ac 
marine: Johnson 

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