Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
448 am PDT Wednesday Apr 1 2015
Synopsis...cool and breezy conditions will persist through late
Wednesday night. Overnight lows tonight and Thursday night will be
colder than normal especially in sheltered locations. Daytime
temperatures will warm slightly by the end of the week as high
pressure builds over the area. Rain may be a possibility beginning
Sunday lasting into early next week.
Discussion...as of 3:00 am PDT Wednesday...temperatures have
finally started to cool off compared to 24 hours ago with many
locations now running 4 to 8 degrees lower. After a very breezy
day on Tuesday into Tuesday evening winds have slowly diminished
overnight although with a shortwave forecast to move through this
evening plus a tighter surface gradient northwesterly winds
should increase with gusts along local peaks expected to be 30 to
40 miles per hour. Will likely see a few locations approaching 50 miles per hour. Urban
spots will generally see 10 to 20 miles per hour speeds with gusts up to 30
miles per hour in wind- prone locations.
Big forecast question for tonight involves lows as the reinforcing
colder air will help to drop temperatures while wind speeds should help
to keep them elevated enough to mitigate frost concerns. Latest
guidance continues to show isolated North Bay spots getting close
to 35 degrees but generally staying in the upper 30s to lower 40s.
Thursday night is a bigger concern as clear skies plus lighter
winds will help to bring temperatures down into the 30s for the North Bay
plus portions of Monterey and San Benito counties. A frost
advisory may need to be issued for that period especially since
the potential impact on agriculture.
Temperatures will slightly warm for Thursday and Friday as a weak ridge
of high pressure builds back to our County Warning Area. Daytime readings will
generally be 60s at the coast with 70s inland. The ridge will
flatten out by Saturday as a longwave trough approaches the coast.
That trough will play a key role in the weather next week. Various
computer models are finally in better agreement that moisture
associated with the trough will move to our area as early as Sunday.
The big change from yesterday is evident on the GFS which now has
the main low moving south to the Washington coast. That compares
to previous runs that had the low off the British Columbia coast. Bigger
question is what will happens by next work week. Various models
generally show at least 2 good shots of picking up at least some
rain although there is less agreement on the timing. Probability of precipitation were
mostly put in the chance category. Wpc 7 day quantitative precipitation forecast product shows 1/4
to 1/2 inch for most of sf Bay with up to 3/4 of an inch for the
North Bay. For locations to the south less than 1/4 of an inch is
depicted. Worth noting that the dgex...GFS operational...GFS
ensemble mean...and Gem all have higher precipitation values over the
next 7 days. European model (ecmwf) numbers are the lowest and are the closest to
the wpc numbers.
Aviation...as of 04:45 am PDT Wednesday... widespread VFR today.
Main issue will be another round of gusty winds... however peak
gusts should top out somewhat lower than values reached yesterday.
Ksfo likely to be windiest spot today.
Vicinity of ksfo...VFR. West winds. Afternoon peak gusts up to 30
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. West winds. Afternoon peak
gusts around 20 knots.
Marine...as of 04:43 am PDT Wednesday...moderate to strong north
to northwest winds will persist through the forecast period. Local
gale force gusts will be possible. Building northwest swell in
conjunction with building fresh swell and mixed seas will lead to
hazardous maritime conditions along the central coast.
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt 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
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...Monterey Bay from 2 PM
Public forecast: Bell
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