Weather

346 
fxus66 kmtr 280530 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
946 PM PDT Wednesday Aug 27 2008 


Discussion...as of 9:46 PM PDT Wednesday...stratus continues to 
slowly creep up the coast this evening while a few high clouds 
embedded in the upper level anti-cyclonic flow traverse the 
northern half of the region. The Fort Ord profiler is gradually 
beginning to hint at a marine layer however it remain fairly 
shallow below 1000 feet. The northerly gradient from acv-sfo continues 
to strengthen and now stands at 7.8 mb only slightly stronger than 
24 hours ago. A southerly gradient from smx-sfo of around 2.0 mb 
struggled against the stronger northerly gradient earlier today 
bringing the stratus as far north as the Monterey Bay. However latest 
satellite imagery show the southerly gradient losing and stratus 
beginning to retreat. 


Temperatures across the board rose significantly today over yesterday 
with many locations up 9 to 10 degrees. The southerly stratus surge 
caused Big Sur to remain steady at 83 degrees while Santa Cruz 
only made it to 76 degrees...2 degrees lower than yesterday as a 
result of the fog bank that moved in this afternoon. With the 
exception of Santa Cruz coastal and Bay regions saw temperatures in 
the upper 70s and 80s with inland locations reaching into the 90s to 
low 100s. San Rafael managed to tie its old record of 97 that was 
set back in 1993. 


The forecast remains on track with continued warming Thursday. Will 
not make any changes to the heat advisories that have been issued 
(please see sfonpwmtr or WMO header wwus76 kmtr for details). Models 
depict continued offshore flow as high pressure continues to build 
into the Great Basin and heights of 592 dm with 850 mb temperatures of 28 
degrees celsius. The NAM depicts winds of 20-35 knots at 925mb over the 
north and East Bay hills. This will result in very warm temperatures 
and gusty offshore flow...the combination of which has resulted in a 
red flag warning over the north and East Bay hills until 8 am 
Friday and a heat advisory for portions of the area on Thursday and 
and the Santa Clara Valley into Friday. 


High pressure over the Great Basin will weaken Friday bringing a 
return of the onshore flow. An approaching upper level trough will 
bring a cooler airmass to the region and a return of the marine layer 
and hence cooler temperatures...especially at the coast. Long range 
models have high pressure ridging over the Pacific northwest again next week 
however model need to come to a consensus as for the timing of the 
event. Nonetheless it appears we are in for another offshore wind 
event early next week. 


&& 


Fire weather...as of 2:55 PM PDT Wednesday...the red flag warnings 
for the north and East Bay hills will be extended through 8 am 
Friday. 


The nam12 is indicate northeast winds up to 20-30 knots in the north and 
East Bay hills tonight into Thursday morning...with winds decreasing 
Thursday. Winds will pick up again Thursday night into Friday morning 
with the red flag warning extended through 8 am Friday. As was 
stated in the previous discussion...the latest model solutions are 
now more in line with a typical offshore wind event for the north and 
East Bay hills although it is by no means an extreme wind event. 


Will have to watch for another potential offshore wind event with the 
gfs40 bringing 30 knot northeast winds by Labor Day morning to the 
north and East Bay hills. 


&& 


Aviation...as of 10:25 PM PDT Wednesday...VFR conditions to 
continue all night except for perhaps near the Monterey Bay where a 
shallow marine layer has pushed into from the south. The northerly 
surface pressure gradient continues to be strong from Arcata to San 
Francisco (7.2 mb) therefore the fog surge is not expected to move 
much farther north than the current location. Winds are expected to 
remain light at all terminals overnight. 


&& 


Mtr watches/warnings/advisories... 
... Arena to Pigeon pt 20-60 nm 
pt Arena to Point Reyes 0-20 nm 
San Francisco Bay until midnight. 
.Red flag warning for the North Bay and East Bay hills 
(zones 507 and 511) until 8 am Friday. 
.Heat advisory for San Francisco...San Francisco Bay 
shoreline...East Bay interior valleys...and the Santa 
Clara Valley from noon through 8 PM Thursday. 
.Heat advisory for the Santa Clara Valley from noon 
through 8 PM Friday. 


$$ 


Public forecast: c walbrun 
aviation/marine: Anderson 
fire weather: r walbrun/mhs/Larry 


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