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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 55 °
• Low: 39 °
• Rain Showers

• Tuesday
• 
• High: 54 °
• Low: 39 °
• Chance of Rain

• Wednesday
• 
• High: 59 °
• Low: 41 °
• Partly Cloudy

• Thursday
• 
• High: 61 °
• Low: 41 °
• Partly Cloudy

• Friday
• 
• High: 61 °
• Low: 45 °
• Partly Cloudy

Area forecast discussion 
National Weather Service San Francisco Bay area 
852 PM PST sun Feb 12 2012 


Discussion...as of 8:52 PM PST Sunday...currently the infrared 
satellite image is showing a cold front passing over the forecast 
area. Kmux is showing showers associated with the cold front 
moving over the area from the northwest to the southeast. So far 
precipitation totals have been less than a tenth of an inch with a 
few reports in the North Bay around fifteen hundredths of an inch. A 
bulk of the steady precipitation should be over with shortly after 
midnight as the cold front moves off to the east. 


Monday morning may still see a few showers as cold air moves in 
aloft. According to the 0000z nam12 500mb temperatures will drop 
to negative 20 to 24 degrees celsius which will allow lapse rates 
from 1000 to 500 mb to reach 6.75 to 7.25 degrees c per 
km...supporting shower activity through Monday afternoon. The 
airmass will dry out behind the cold front so precipitation values 
shouldn't be to great with these showers. Overnight temperatures 
for Monday night will be fairly chilly with a cool airmass in 
place. Expect lows along the coast in the upper 30s to low 40s and 
low to middle 30s inland. 


Previous discussion...model guidance is far from cut-and-dry for 
the remainder of week with some of the solutions depicting at 
least two decent shots of rain while others keep US mostly dry for 
the week. The first shot would by Tuesday/Wednesday as a system drops from 
the pacnw close to our area. Even the most bullish of solutions 
indicate less than 1/10" of rain from this. After a couple days 
dry weather due to ridging from the Pacific...the second possible 
bout of rain one would be Friday into late Saturday as another 
system drops from the pacnw. The one over the weekend has more 
moisture to use plus a more favorable trajectory...therefore probability of precipitation 
were increased a bit for that period. Rainfall totals are not 
expected to amount to much with this system. 


It is Worth noting that even if we do not receive any additional 
rainfall the hemispheric pattern will be favorable for cool 
weather and a close system will provide ample clouds. The warm 
sunny weather we had last week is not anticipated to return the 
next 7 days. 


&& 


Aviation......as of 5:00 PM PST Sunday...low clouds have 
persisted along the coast all day including the mry Bay area. 
Middle and high clouds cover the sfo Bay area. Patchy MVFR ceilings and 
drizzle are being reported in the East Bay as of 01z but this is 
expected to be short-lived. Main rain from the approaching storm 
will arrive in the sfo Bay area 04-05z and the mry Bay area 07-08z. 
Ceilings lowering but remaining in the VFR range until the front 
passes after 08-09z when ceilings will drop to MVFR range. Winds will 
shift to the south to southwest just ahead of frontal passage. 
West to northwest winds increasing after frontal passage. 


Vicinity of ksfo...ceilings lowering but remaining VFR through 08z. 
Becoming MVFR after 08z after frontal passage. Light rain 
beginning around 04-05z. Winds may switch briefly to south to 
southwest between 04z and 08z ahead of frontal passage but will 
switch to west to northwest after 08z. Winds will ramp up later 
tonight with gusts over 20 knots by Monday morning. 


Ksfo bridge approach....similar to sfo. 


Monterey Bay area terminals...MVFR ceilings. Light rain beginning 
around 07-08z continuing through 13-15z. 


&& 


Mtr watches/warnings/advisories... 
... Arena to Pigeon pt 10-60 nm from 9 PM 
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 2 am 
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm from 1 am 
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm from 3 am 
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 3 am 
Small Craft Advisory...rough bar advisory for sf bar 


&& 


$$ 


Public forecast: Larry/Bell 
aviation/marine: west pi