Area forecast discussion 
National Weather Service San Francisco Bay area 
1029 am PDT sun may 1 2016 


Synopsis....offshore winds will continue today...resulting in 
sunny and warm conditions in most areas. Coastal fog and low 
clouds will likely return by late today or tonight. Seasonable 
and dry weather is forecast Monday and Tuesday. A weather system 
will approach California by the middle of the week...bringing a 
chance of showers from late Wednesday through the end of the 
week...along with cooler than normal temperatures. 


&& 


Discussion...as of 8:45 am PDT Sunday...clear start to the day 
with a moderate offshore flow in place. North-to-S gradient right now 
is over 2 mb while west-to-E flow is slightly from the east. As the 
previous discussion mentioned, models are indicating a southerly 
push up the coast today although current satellite does not show 
any clouds even up to slo County. 14z run of the hrrr does 
indicate southerly winds will set up over the next few hours, so 
will keep a close eye on the satellite to see if it does 
materialize. 


Current forecast on track so no updates planned at the moment. 


Previous discussion...skies are clear across our entire forecast 
area early this morning as light offshore flow continues. Current 
temperatures are generally warmer than 24 hours ago and in some 
cases several degrees warmer. Forecast guidance indicates high 
temperatures today will be about five degrees warmer than 
yesterday. However...models forecast an end to offshore flow today 
along with the development of southerly flow along the coast. This 
does not look like a classic "southerly surge" scenario...since 
low clouds do not already exist to our south near Point 
Conception. What's more likely to happen is that low clouds and 
fog will form in coastal areas from Monterey Bay south by early 
afternoon...and then move north up along the rest of our coast 
late this afternoon and evening. This makes for a difficult 
temperature forecast today for coastal areas since the timing of 
the southerly wind onset and coastal fog development will have a 
big impact on temperatures. Most likely scenario is for cooling to 
occur in locations like Big Sur and Santa Cruz while other coastal 
areas will be as warm or warmer than yesterday. 


Another item to watch today is a shortwave trough currently over 
southeast Oregon that is rotating around a longwave trough 
centered over the desert SW. This shortwave is forecast to rotate 
into northern and central California later today. The European model (ecmwf) keeps 
all precipitation associated with this shortwave to our east...mainly over 
the Sierra Nevada. However...both the 00z NAM and 00z GFS 
forecast isolated showers along the eastern fringes of our 
forecast area late this afternoon and early this evening. Have 
therefore added slight chance probability of precipitation to far eastern Alameda...Santa 
Clara...and San Benito counties for later today. 


Dry and mild weather is forecast for Monday and Tuesday. Onshore 
flow will likely maintain at least areas of night and morning low 
clouds and temperatures will be near normal. 


An upper trough currently seen on satellite imagery offshore along 
145w is forecast to gradually approach the California coast over 
the next three days and begin to generate shower chances across 
our area by late Wednesday. Both the GFS and European model (ecmwf) forecast a 
cutoff low to develop near San Francisco by Thursday...with that 
low then projected to drop southeast and track across Southern 
California by late Friday and Friday night. Thus...shower chances 
will continue through the end of the week and probably into next 
weekend as well. Given the unpredictability of cutoff low 
movement...it's difficult to pinpoint where shower chances will be 
greatest during the second half of the week. Isolated thunderstorms 
may also occur...but will wait to add thunderstorms to the 
forecast until confidence increases on the timing and track of the 
upper low. In addition to precipitation chances...this upper low 
will result in cooler than normal conditions across most of our 
area during the second half of the week. 


&& 


Aviation...as of 10:30 am PDT Sunday...dry offshore flow keeping 
VFR today. The one fly in the ointment in the forecast is a 
possible southerly surge later today. Latest NAM and WRF show a 
southerly surge impacting kmry/ksns...poss making it into sf Bay 
overnight. Conf is marginal. 


Vicinity of ksfo...VFR. 


Sfo bridge approach...similar to ksfo. 


Monterey Bay terminals...VFR becoming MVFR late this evening and 
overnight. 


&& 


Marine...as of 8:45 am PDT Sunday...high pressure over the 
eastern Pacific will keep northerly winds over the coastal waters 
today. Locally gusty winds will be possible over the outer waters 
north of Point Reyes. Southerly winds will develop late tonight 
and early Monday. A moderate swell will mix with a smaller long 
period southerly swell this week. 


&& 


Mtr watches/warnings/advisories... 
... 


$$ 


Public forecast: Bell/dykema 
aviation: Sims 
marine: Sims 




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