Scientific Forecaster Discussion
fxus66 kmtr 240012
Area forecast discussion
National Weather Service San Francisco Bay area
512 PM PDT sun Apr 23 2017
Synopsis...mostly clear this evening and overnight then
increasing clouds towards dawn as the next front approaches.
Expect some light rain in the North Bay Monday morning with a few
light rain showers reaching from the Golden Gate to Monterey Bay
Monday afternoon and early evening. Another weak front will keep a
slight chance of North Bay rain showers in the forecast Tuesday
into Wednesday but dry and seasonably cool from San Francisco
southward. Dry on Thursday then breezy winds develop into Friday
with a warming trend next weekend as high pressure builds.
Discussion...as of 1:59 PM PDT Sunday...its a sunny and mild
Sunday afternoon with highs in the 60s to lower 70s. Expect a
clear but cool evening with west winds off the ocean ushering in
some cool marine air overnight with sea surface temps back into
the mid 50s.
Next weather system will arrive by around sunrise Monday as mostly
cloudy skies greet the day. Some light rain should reach northern
Sonoma County by 15z Monday with light rain impacting the North
Bay Monday morning commute. Rain totals will be very light only a
few hundredths or perhaps a tenth of an inch but enough to wet the
roads and turn on the wipers. Periodic light rain or showers will
reach the Golden Gate and extend southward towards Monterey Bay
later Monday afternoon. Expect nothing more than some nuisance
light rain and most cells shouldn't penetrate too far inland. The
combination of cloud cover and onshore winds will keep daytime
highs seasonably cool in the mid 60s for most locations.
Yet another weak front will move into the North Bay on Tuesday and
keep at least a slight chance of showers in the forecast. Best
chances will be from Mendocino north with little or no chance
south of the Golden Gate. Forecast was fine tuned to try and keep
slight chance pops confined to the North Bay Tuesday and then
again weds as a final front rides over the ridge and tries to
bring some light rain to the North Bay region. All this talk of
North Bay rain should only add up to very light amounts of rain
through weds (trace to a couple tenths), while the rest of the Bay
area looks to remain dry and with seasonable or temps a few
degrees below normal.
The longwave pattern will start to shift by Thursday with a trough
digging over the Great Basin. This will set up some strong surface
pressure gradients across the state and will need to watch wind
potential, especially over our hills on Friday as gusty north
winds develop. Latest ECMWF then builds a warm ridge with some
lighter offshore winds next weekend suggesting dry and mild
weather to wind out the month of April. Long range models keep the
forecast dry as we head into may.
Aviation...as of 4:54 PM PDT Sunday...for 00z tafs. Mostly clear
skies present at the moment with increasing mid and high clouds
expected through the night. Moderate and gusty west winds will
prevail through this evening diminishing a bit overnight. MVFR
cigs possible over select terminals early Monday morning however
confidence is low regarding cigs and timing.
Vicinity of ksfo...VFR through much of the period with tempo MVFR
cigs expected between 09z and 13z Monday morning. Confidence is
low regarding cigs and timing. West to southwest winds 15-25 kt
anticipated through this evening with gusts to 25-30 knots
possible. Winds will east to around 10-15 kt overnight before
ramping up again Monday afternoon.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals..VFR through much of the period with MVFR
cigs expected after 10z Monday morning. Clearing is forecast
around 19z-20z. Confidence is low regarding cigs and timing. West
to southwest winds 10-15 kt anticipated through this evening.
Winds will east to around 5 kt overnight before increasing to
around 10 kt with gusts to 15 kt Monday afternoon.
Marine...as of 2:03 PM PDT Sunday...moderate northwesterly can
be expected along all of our waters through the forecast period
with the highest speeds near the coast. Winds and seas will
dramatically increase by Thursday as the surface pressure
gradient tightens along the California coast.
... Bay until 3 am
Small Craft Advisory...mry Bay until 3 am
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm until 3 am
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm until 3 am
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Public forecast: rww
Visit US at www.Weather.Gov/sanfrancisco