Area forecast discussion 
National Weather Service San Francisco Bay area 
1106 am PDT Sat Sep 24 2016 


..very warm to hot weather conditions Sunday and Monday... 


Synopsis...a strong ridge of high pressure will build over our 
region through the weekend resulting in very warm to hot 
conditions on Sunday and Monday. In addition, offshore flow will 
develop this weekend, allowing very warm conditions to develop all 
the way to the coast by Sunday. A cooling trend is forecast from 
Tuesday through Thursday. 


&& 


Discussion...as of 09:01 am PDT Saturday...clear skies prevail 
over the region this morning with low clouds staying well offshore 
as high pressure builds in over the region. Temperatures at the 9 
o'clock hour are running a few to as much as 11 degrees warmer 
compared to 24 hours ago, evidence of the region-wide warming 
trend expected through the weekend. With that said, the ongoing 
forecast remains on track for today and no updates are needed at 
this time. Please see the previous discussion below for additional 
details. 


&& 


Previous discussion...as of 3:40 am PDT Saturday...early morning 
satellite imagery shows fog and low clouds lurking a short 
distance offshore and we may see patchy fog develop up along the 
coast by sunrise. There could be local dense coastal fog as well. 
The Fort Ord profiler shows the marine layer is very shallow (500 
feet deep or less) and onshore flow is weak this morning. 
Therefore, any morning fog should remain confined to the immediate 
coast and this will be the last our area will see of fog or low 
clouds through at least Monday. 


Early morning water vapor satellite imagery shows an upper ridge 
building offshore along 135w...and shifting eastward towards the 
California coast. The impact of this ridge is already evident on 
The Fort Ord profiler which shows significant airmass warming just 
above the shallow marine layer. As a result of this airmass 
warming and lighter onshore flow today, today's high temperatures 
are expected to be about 10 degrees warmer than yesterday. 


The warming and drying trend will continue into Sunday as the 
upper ridge builds inland over California. In addition, a surface 
high is forecast to strengthen to our north and east, setting up 
offshore flow tonight into Sunday. The models have been trending 
stronger with this offshore flow, especially across the North Bay 
mountains where the latest WRF forecasts surface winds over the 
ridges as high as 25g40 knots late tonight and Sunday morning. 
These offshore winds will not only generate critical fire weather 
conditions tonight and Sunday in the North Bay mountains (see fire 
weather section below), but also result in stronger warming going 
into Sunday, especially in coastal areas. Forecast high 
temperatures have been nudged higher for Sunday, especially in the 
North Bay and near the coast. Highs by Sunday are projected to be 
in the 80s and lower 90s at the coast, and in the 90s to 105 
inland. Record highs are possible. A heat advisory remains in 
effect for our entire forecast area from 11 am to 8 PM Sunday. 


Some earlier model runs had indicated a potential for slight 
cooling on Monday, especially near the coast where light southerly 
winds are expected to develop. However, latest models indicate a 
very warm and dry airmass persisting over our area through Monday 
with little or no relief expected from the heat, even at the 
coast. It now appears that for many locations Monday may end up 
being the warmest day. A heat advisory is also in effect for our 
entire forecast area from 11 am to 8 PM Monday. This upcoming heat 
event will almost certainly be more oppressive then the event last 
Sunday and Monday, especially at the coast. 


The models agree that a cooling trend will occur from Tuesday 
through Thursday of next week as the upper ridge breaks down and 
moves off to our east and an upper trough drops in from the 
northwest. Temperatures by Thursday are forecast to be as much as 
20 degrees cooler compared to Monday. 


&& 


Aviation...as of 11:05 am PDT Saturday... high pressure will 
bring VFR conditions with clear skies and light winds today. 
Afternoon sea breeze up to around 10-20 knots along the coast. 


Vicinity of ksfo...VFR. Light winds, except this afternoon where 
winds may increase to 15-18 kt. Occasional gust to mid 20 kts 
posbl. 


Sfo bridge approach...similar to ksfo. 


Monterey Bay terminals...VFR through the period. Generally light 
winds with a weak afternoon sea breeze. 


&& 


Fire weather...as of 3:30 am PDT Saturday...latest models 
continue to trend towards stronger offshore winds tonight and 
Sunday morning, especially in the North Bay mountains. 00z WRF 
model forecasts sustained north to northeast winds of 30 mph with 
gusts as high as 45 mph across the higher ridges of northern Sonoma 
and Napa counties late tonight through Sunday morning. In 
conjunction with these winds will be very warm to hot daytime 
temperatures and little or no nighttime humidity recovery. 
Therefore, a red flag warning will be issued for the North Bay 
mountains (fire weather zone 507). The red flag warning will be in 
effect from 9 PM Saturday evening until 3 PM Sunday. Otherwise, 
expect the warming and drying trend to continue into Sunday and 
Monday across the entire district. Winds will generally be light 
after Sunday. A cooling trend will begin on Tuesday. 


In the vicinity of the soberanes fire: portable RAWS stations 
above 3000 feet are currently reporting northeast winds of 10 to 
15 mph with gusts up to 20 mph. Winds in this area are forecast to 
decrease slightly by this afternoon and then gradually turn to the 
south tonight and to the southwest by Sunday afternoon when they 
will increase slightly again. Wind speeds are not expected to 
increase much beyond their current magnitude through the 
remainder of the weekend, however temperatures will climb through 
Sunday while relative humidity values drop into the single digits. Hot and very 
dry conditions will then continue through Monday. In fact, Monday 
will probably be the warmest and driest day, with gradual 
improvement expected to begin on Tuesday. 


&& 


Climate...here are the record highs for September 25 and 
September 26. 


September 25 September 26 
record/year record/year 
Bay area 


Kentfield.............100/1964.....................99/1921 
San Rafael............100/1964.....................99/1963 
Napa..................101/1960....................105/1963 
San Francisco..........93/1954.....................94/1992 
sfo....................91/1970.....................95/1958 
Oakland museum.........95/1978.....................93/1973 
Oakland Airport........94/2010.....................97/1958 
Richmond...............95/1964.....................95/1963 
Livermore.............101/1978....................103/1952 
Mountain View..........91/1978.....................95/1999 
San Jose...............97/1952.....................98/1963 
Gilroy................106/1978....................104/1963 


Monterey Bay area 


Monterey...............95/1954.....................98/1970 
Santa Cruz............100/2010....................101/1970 
Salinas................97/1960....................100/1970 
Salinas Airport........99/1937.....................99/1970 
King City.............105/1975....................105/1963 


&& 


Marine...as of 10:54 am PDT Saturday...a gradually easing 
pressure gradient will continue to result in moderate northwest 
winds through the day today for most of our waters. The strongest 
winds will be this afternoon and this evening along the Sonoma and 
Big Sur coasts. Locally generate fresh swell may also result in 
hazardous conditions. Winds decrease Sunday. 


&& 


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


&& 


$$ 


Public forecast: rgass 
aviation: drp 
marine: drp 
climate: BAM 
fire weather: dykema 




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