Area forecast discussion 
National Weather Service San Francisco Bay area 
438 PM PST Friday Jan 30 2015 


Synopsis...dry conditions are expected to continue into next 
week with chances of rain only over far northern California. 
Temperatures will remain several degrees above normal for the next 
week. There are indications that rain may move back into the area 
by the end of next week. 


&& 


Discussion...as of 01:28 PM PST Friday... 
morning fog has dissipated and given way to another mostly sunny 
day with a few clouds lingering along the immediate coastline. 
Temperatures have climbed into the 60s and lower 70s in yet 
another above normal day. The upper low in Southern California 
will continue to strengthen and lift eastward overnight as a 
strong ridge over the Pacific will build back into the area. This 
will bring in some drier air and will temper the extent of 
overnight fog tonight with more favorable conditions existing 
earlier overnight. The ridge will build into the area over this 
weekend and bring dry and sunny conditions along with well above 
normal temperatures again. Readings from the middle 60s to middle 70s 
will be common on Saturday and Sunday with the ridge of high 
pressure dominating. This will be a repeating theme as there will 
be a shot of precipitation again into far northern California but unable 
to make it south due to the ridge of high pressure on Monday. The 
ridge will hang strong through the end of the week with dry 
weather and above normal temperatures. 


Finally some hope on the distant horizon...as the European model (ecmwf) and GFS 
remain with a fairly consistent solution of rainfall arriving by 
late Thursday into Friday. Both show the ridge being suppressed 
well south and then the pattern becoming more conducive for storm 
systems to push into the Bay area. Have increased probability of precipitation 
considerably in the far extended periods and if the solutions 
remain consistent this could be our first rain in quite a long 
time. The last measurable rain in downtown San Francisco was December 
24 2014. Will have to continue monitoring this as it is promising 
but there is quite a ways to go until it arrives. 


&& 


Aviation...as of 4:40 PM PST Friday...areas of low clouds are 
brushing the immediate coastline this afternoon while skies are 
clear inland. The wmc-sfo pressure gradient is 7 mb directed 
offshore while the acv-sfo and sfo-SAC gradients are 4.7 mb 
northerly and 1.1 mb onshore respectively. The northern extent of 
the coastal low clouds is just barely reaching San Francisco 
placing the cloud cover precariously close to the San Bruno gap 
but the dominant acv-sfo gradient should be sufficient to hold the 
low clouds out of ksfo this evening. Cwsu Oakland research shows 
90% probalility of "no early return" when the sfo-acv/sfo-SAC 
ratio is less than or equal to -1.1 mb...and presently it's -4.7 
mb. On a larger scale...surface high pressure will build over the 
Great Basin tonight and early Saturday morning resulting in 
surface winds in the Bay area trending more solidly over to an 
offshore direction. The 925 mb level rh's dry out appreciably on 
Saturday per the latest NAM model...supportive of a high 
confidence VFR forecast on Saturday. 


Vicinity of ksfo...westerly winds picked up at the top of the 
hour with gusts just over 20 knots...but have since settled back. 
The ocean-land afternoon temperature differential could cause a 
few more brief gusts back up to 20 knots but on the average it 
should hold below. It's a moderate to high confidence VFR forecast 
for the period. 


Ksfo bridge approach...similar to ksfo. 


Monterey Bay area terminals...northwest winds are more efficient at 
pressing low clouds back in over the southern Monterey Bay area. 
The forecast is for a continuation of MVFR ceilings at kmry and ksns 
for tonight and Saturday morning. VFR is forecast to return no 
later than late Sat morning. The locally run 3 km resolution WRF 
model hints at a possible eddy circulation developing over the 
Monterey Bay waters approx 2 am - 5 am Saturday then it dissipates. 
If it actually hangs around longer then maybe the low clouds will 
mix out a bit quicker over the northern Salinas valley while 
tending to stay longer over the southern Monterey Bay area. 


& 


Marine...as of 01:28 PM PST Friday...moderate north winds will 
continue over the coastal waters through Saturday. The strongest 
winds will be at least 10 nautical miles offshore of the coast. 
Patchy dense fog will linger across the North Bay and West Delta 
through noon today. The combination of moderate winds and swell 
may result in somewhat choppy seas as well. Wind and sea 
conditions are expected to improve by tomorrow afternoon. 


&& 


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


&& 


$$ 


Public forecast: Johnson 
aviation: canepa 
marine: Larry 


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