Weather

861 
fxus66 kmtr 112135 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
300 PM PDT Sat Oct 11 2008 


Discussion...as of 2:15 PM PDT Saturday...clear skies with 
cool mornings and warm afternoons through middle week. 


Skies were clear over the entire forecast area this afternoon but 
temperatures are running about 5 to 7 degrees below normal. Winds 
are still breezy in the north and East Bay mountains with gust running 
30 to 40 miles per hour. Most lower elevations are seeing north winds of 5 to 
10 miles per hour. The main forecast issue is how cold will it get in the 
valleys this evening. It is interesting that most of our local 
high res models like COAMPS and WRF run at 3 km are showing very 
warm overnight lows and corresponding very low humidities. Models 
seems to be over-mixing the air down into the valleys and not 
allowing any radiational cooling. This does not seem reasonable as 
once the sun GOES down the boundary layer will decouple and the 
winds will drop quickly. The locations with the best chance for 
frost or near freezing temperatures are the North Bay valleys and the 
Salinas...Carmel and Hollister valleys. So have kept the frost 
advisory for these locations for tonight. 


Should see some warming tomorrow to near or slightly above seasonal 
normals as heights rise to about 575 dm and 850 temperatures rise about 5c 
to near 8c. With winds continuing out of the northeast skies will 
remain clear. Humidities will thus remain low in the hills through 
Monday especially in the north and East Bay areas so the red flag 
warning has been continued in these areas through Monday. See fire 
weather discussion below. May see another morning with frost on 
Monday morning in same locations as for tomorrow morning. This 
will have to be looked at closely tonight or tomorrow. 




Monday and Tuesday will see most areas running 5 to as much as 10 
degrees above normal with lots of 70s and 80s interior valleys 
with few 90s southern Salinas valley. Skies should remain clear and 
winds should finally subside over the north and East Bay mountains 


Extended...Euro and GFS show a slight drop in 500 mb heights late Wednesday 
into Thursday as a minor shortwave moves by to the north. Looks like 
temperatures will remain near or slightly above normal until Friday 
when a baggy trough sets up just offshore. This should allow some 
marine air to begin to push inland late next week and thus have 
included some low clouds and patchy fog wording into the zones 
Friday night into Saturday morning. Temperatures will return to 
more seasonal normals Friday and Saturday with this return of 
onshore flow. Have disregarded the GFS solution for a stronger 
trough for next weekend as its track record in the extended...day 5- 
7 has been poor for the last 4 weeks or so. As mentioned this am 
the Euro has been doing a much better job of picking up on the short 
wave amplifications or lack there of. Euro is now basically 
forecasting a repeat of a trough digging into the Great Basin by 
early next week. This is substantially slower and more amplified 
than the GFS. Will trend to this solution. 






&& 


Aviation...as of 10:20 am PDT Saturday...the latest visible 
satellite image is showing clear skies across the San Francisco 
Bay area. With plenty of dry air aloft and midlevel north 
northeasterly winds dont expect stratus during this forecast 
period. The main forecast challenge for the day will be winds at 
ksfo. At the moment ksfo is reporting 34019 knots and it appears that 
the onshore pressure gradient has increased over the past few 
hours. Therefore expect afternoon winds to reach 25 knots with gusts to 
35 knots...this may change so I will be closely monitoring the winds 
at ksfo this afternoon. Otherwise VFR conditions are expected to 
prevail through the forecast period. 


Monterey Bay area terminals...a beautiful VFR day is in-store for 
the Monterey Bay area today. Winds will be a concern today although 
not nearly as strong as yesterday. Expect the sea breeze to reach 
10 to 15 knots this afternoon at kmry with 20kt expected at ksns. Winds 
are expected to go offshore around midnight therefore I don't 
expect any stratus or fog tonight into the morning hours at kmry or 
ksns. 


&& 


Fire weather...as of 6:00 am PDT Saturday...red flag warning in 
effect through the afternoon for all locations and through Sunday 
afternoon for our higher elevations. Northerly winds with gusts to 30 
miles per hour are possible in all locations through this afternoon while gusts 
to 50 miles per hour are expected to continue over the higher elevation areas. 
Surface observations this morning also confirm the higher speed with 
los Vaqueros gusting to over 50 miles per hour. Conditions in the low lying 
areas will start to improve by this evening as the surface pressure 
gradient diminishes and winds start to subside. For higher 
elevation locations...winds will take longer to subside due to a 
very strong storm system aloft still just to our east. As it moves 
closer to The Four Corners area...winds will start to decrease for 
all areas. Humidity recoveries will mostly be 40 to 60% 
over the higher elevation spots although some local areas may only 
recover into the middle 30s. Look for warmer and drier weather for 
most of next week although winds should be less. 


&& 


Mtr watches/warnings/advisories... 
... Waters through this evening. 


.Tngt through Sunday...Red flag warning for all 
higher elevations. 
... Advisory for North Bay valleys and Salinas 
Carmel and Hollister valleys 3 am to 8 am. 
$$ 


Public forecast: Reynolds 
aviation/marine: Larry 
fire weather: walbrun/dykema 


National Weather Service on the web at weather.Gov/sanfrancisco