Scientific Forecaster Discussion
Return to Local Conditions & Forecast
Area forecast discussion
National Weather Service San Francisco Bay area
453 am PDT sun Apr 20 2014
Synopsis...dry weather and mild temperatures will persist through
Monday afternoon as high pressure remains aloft. A weak storm
system will then bring chances for light rain to the region Monday
night through Tuesday along with cooler temperatures. The
possibility of unsettled conditions then returns for late in the
Discussion...as of 03:45 am PDT Sunday...much less in the way of
low cloud cover this morning compared to previous days as the
marine layer has just about been depleted. As a result...stratus
across the coastal locations around the Monterey Bay northward
over the San Francisco peninsula coast will likely burn off
shortly after sunrise. This, along with a building middle/upper level
ridge, will result in warmer conditions by this afternoon under
mostly sunny skies.
An approaching Pacific storm system will then cool conditions
across the North Bay on Monday while mild temperatures persist
over the central coast. Forecast models indicate only light
precipitation will occur Monday night through early Tuesday as the
middle/upper level system moves inland. With limited moisture
available...rainfall amounts will likely remain below one-tenth of
an inch across the North Bay with only a few hundredths possible
further south. Cooler and drier air will then filter in behind the
exiting trough on Tuesday with rain chances quickly diminishing
early in the morning. Temperatures are only forecast to warm into
the middle 50s to middle 60s region wide Tuesday afternoon.
Dry conditions along with a slight warming trend will resume
Wednesday and Thursday as the middle/upper level ridge builds along
the West Coast. The medium range forecast models then diverge in
their solutions of the middle/upper level pattern for late in the
work week through next weekend. The GFS and Gem drop a deeper
middle/upper level trough out of the Gulf of Alaska late in the week.
This system would likely bring increased chances for rainfall to
the region late Friday through Sunday. However...the European model (ecmwf) is much
less aggressive with precipitation amounts during this time frame.
Will keep slightly cooler conditions and slight chances of
precipitation in the forecast for next weekend until model
consistency improves in the coming days.
Aviation...as of 4:50 am PDT Sunday...stratus clouds can be seen
on satellite imagery this morning from Half Moon Bay south to the
Monterey peninsula. IFR ceilings and visibilities are reported
along the immediate coast. Inland skies are mostly VFR with
exception of ksts reporting occasional 2 miles or less in fog.
Subsidence will continue through this morning as the 500 mb height
ridge strengthens just a little more before heights begin to trend
to the downside beginning Monday morning as a trough approaches from
the northwest. The subsidence today will tend to cause additional
low level warming which will in turn help reinforce the marine
layer inversions. All of this means there's good chances the
marine based clouds will tend to stay on the immediate coastline
today...bettering the odds that VFR will prevail over the Bay
area today. By tonight boundary layer humidities lower appreciably
but it's still possible that kmry and ksns pick up scattered-broken (ifr)
cloud coverage under a more compressed marine layer.
Vicinity of ksfo...VFR. Marine layer inversion depth may support
some westerly wind gusts to 20 knots 21z-04z.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...IFR ceilings are reported this
morning. Ceilings should mix out by 18z. Low confidence forecast
this evening regarding low clouds returning. There's decent low
level 925 mb level drying noted on the NAM model. If low clouds
return this evening they may just be around briefly before
reverting back to VFR conditions.
Marine...as of 4:50 am PDT Sunday...large northwest swell with longer
periods will move into the waters today and tonight. A high surf
advisory is in effect until 5 am PDT Monday. Northwest swell will
reach 13 to 15 feet with a 16 second swell period.
... Surf advisory...coast from Sonoma County to Monterey County
until 5 am PDT Monday morning
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm until 6 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm until 6 PM
Small Craft Advisory...rough bar advisory for sf bar
Public forecast: rgass
Visit US at www.Weather.Gov/sanfrancisco
Follow US on facebook, twitter, and youtube at: