Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
826 PM PDT sun Mar 9 2014
Synopsis...a cold front associated with a Pacific storm system
will slowly spread rain south overnight with the main focus
remaining over the North Bay. Generally light rain is expected as
this cold front passes over the area. Dry weather is forecast
from Monday afternoon through the remainder of the week into next
weekend. Daytime temperatures will be above normal from Tuesday
Discussion...as of 8:26 PM PDT Sunday...the latest infrared satellite
image continues to show a cold front slowly advancing through
northern California. The 0000z koak upper air sounding is showing
quite a bit of dry air below 10000 feet. Before any precipitation
hits the ground this dry layer will have to become saturated.
Therefore expect generally light precipitation if any out of the
approaching front. Satellite and GPS derived blended total precipitation
water is showing around 1.2 inches just off of the Sonoma coast so
it is not out of the question that the atmosphere will moisten up
enough for some light rain. Kmux Doppler radar is also showing a
few weak echos of precipitation approaching the coast as well.
Time height analysis utilizing the 0000z NAM bufr run is showing
frontal passage in the San Francisco Bay area to occur between 4
am and 7 am so there may be some wet roadways around for the early
morning commute. Slightly later frontal passage is expected in the
Monterey area with arrival between 7am and 10am...even less rain
is expected in Monterey than in San Francisco. Gusty north winds
are expected behind the cold front Monday afternoon...so expected
a breezy afternoon around the forecast area.
The 1200z European model (ecmwf) and 1800z gfs40 have initialized well with the
current synoptic pattern and remain in good agreement with a ridge
of high pressure building over the eastern Pacific Tuesday. This
ridge will promote dry warm conditions through at least next
weekend. The current forecast package depicts this scenario well
so no updates are necessary at this time.
Previous discussion...as of 3:00 PM PDT Sunday...kmux radar
continues to pick up a few showers streaming across the far North
Bay this afternoon, although virtually all of the recorded rain is
still to our north. Models are in good agreement that as a
shortwave trough advances to the West Coast tonight, rain will be on
the increase for our area -- especially over the North Bay. Precipitable water
amounts are plentiful -- over an inch -- so the storm would have
the potential to drop decent rainfall if the dynamics lined up
with it. Current forecast is only slight changed from the previous
shift with locally an inch possible for the North Bay mountains, a
quarter to half for most North Bay communities, 5 to 15 hundredths
around sf Bay, and lesser amounts to the south. Would not be
surprised if almost all of Monterey and San Benito counties came
away without any rainfall.
Cooler temperatures (4-8 degrees) can be expected on Monday as
the trough passes through. That should be the coolest day of the
week for almost all spots. Offshore winds will start to crank up
Monday night into Tuesday as a ridge of high pressure at the
surface builds to our north. This will help to produce locally
gusty winds in the hills for that period.
Starting on Tuesday temperatures will begin to warm as an offshore
flow at the surface combines with a ridge of high pressure aloft
and warming at 850 mb. The warming will generally increase into
the weekend with possible record breaking highs for Sunday. Would not
be surprised if we see a few 90s on that day in Monterey County.
Longer range guidance shows dry weather continuing through at
least to the 21st of the March.
Aviation...as of 5:50 PM PDT Sunday...a cold front off the coast
will bring some MVFR ceilings to the area late tonight. Occasional
light rain will reach the sfo Bay area early Monday morning.
Vicinity of ksfo...VFR through the Airport evening rush. MVFR late
tonight after 10z. Some light rain possible 12z-16z.
Ksfo bridge approach...same as sfo.
Monterey Bay area terminals...MVFR ceilings after 12z.
Public forecast: Larry
aviation: west pi
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