Area forecast discussion
National Weather Service San Francisco Bay area
1019 am PDT Wednesday may 22 2013
Discussion...as of 9:40 am PDT Wednesday...sunny start to the day
today for our entire County Warning Area plus waters so issued a minor forecast
update. Temperatures are running 5 to 10 degrees cooler compared
to yesterday in spots as the cold air advection expected to impact our area has
moved across. Although the sun will help today, still look for
cooler than normal temperatures -- 55 to 65 at the beach with 60s
and 70s inland.
The models also seem to be verifying nicely with the winds as the
number of stations over 30 miles per hour has dropped off quite a bit
compared to Tuesday. 925 mb speeds were expected to be lower today
and so far that does look like it's playing out. There will still
be a few breezy pockets over the afternoon, but nothing like what
we saw yesterday.
Storm system over the pacnw will remain fairly stationary through
Friday keeping US in a cooler than normal flow. Over the weekend a
piece of energy from the Gulf of Alaska will become entrained in
the flow and keep the system still over the pacnw/British Columbia area.
Although temperatures will remain on the cool side...right now
looks like most spots will see sunshine during the day. Possible
that coastal areas could see overnight clouds with some patchy fog starting
Friday night.
Will take a closer look at the middle of next week when the models
indicate a longwave trough moving to the coast and possibly
spreading rain into our County Warning Area.
Previous discussion...cool dry air continues to filter into the
region overnight...as an upper level low pressure system remains
stalled over the Pacific northwest coast. Temperatures cooled into
the middle 40s to low 50s so far...and are forecast to fall another 5
degrees in the next few hours...with readings mainly in the 40s.
Otherwise...moderate northwest winds continued across the region
well into the overnight hours...as surface high pressure dominated
the eastern Pacific...with a surface low over southern Nevada.
Wind gusts over 20 miles per hour were common through the area and are
forecast to slowly subside into the early morning hours.
The upper low over the Pacific northwest will dominate the weather
pattern through the end of the work week...with daytime high
temperatures reaching the 60s along the coast...and near 70
inland. These temperatures are around 5 degrees below normal for
the middle of may. Gusty north to northwest winds will also be
present across the region each afternoon into the evening hours.
One of the more difficult parts of the forecast into the weekend
will be the possibility of low clouds along the coast. The short
term models indicate that boundary layer relative humidity values increase along
the coast over the next 24 hours...however...numerical guidance
indicates the coast will remain clear. With the lack of a marine
layer...decided to keep out any mention of low clouds along the
coast. If low clouds do form...they will likely be very patchy in
nature.
No major changes in the weather pattern until the first part of
next week. The upper low off the Pacific northwest coast is forced
east into the Great Basin Monday into Tuesday as a more powerful
storm in the Gulf of Alaska moves slowly southeast toward the
region. Both the GFS and European model (ecmwf) are in good agreement about chances
of precipitation and timing of rain adding confidence to the
forecast. The medium range models indicate the rain will quickly
spread from north to south along the coast Monday into Tuesday.
The greatest chance for rain will remain over the North Bay. We
will continue to monitor the chances for rain closely into the
weekend and provide more specific information regarding timing and
amount of rain as the event nears.
Otherwise...the climate prediction centers 8 to 14 day outlook
(valid from may 29th through June 4th) call for below normal
temperatures!
&&
Aviation...as of 10:15 PM PDT Wednesday...VFR conditions through
the forecast period with mainly high clouds. The bigger story
will be the gusty winds. Breezy conditions exist now...but winds
should ramp up this afternoon.
Vicinity of ksfo...VFR. No real change from previous forecast.
Winds are expected strengthen to around 30 knots with gusts to 40 knots after
20z. An Airport weather warning for winds remains in effect from 20z
(1 PM pdt) this afternoon to 04z (9 PM pdt) this evening.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. Moderate and locally gusty
west winds will continue through the forecast period. Strongest
winds expected this afternoon.
&&
Mtr watches/warnings/advisories...
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
glw...pt pinos to pt Piedras Blancas 0-10 nm
glw...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...rough bar advisory for sf bar
Small Craft Advisory...sf Bay from noon
Small Craft Advisory...mry Bay from noon
&&
$$
Public forecast: Bell/Riley
aviation/marine: mm
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