Scientific Forecaster Discussion
fxus66 kmtr 221151
Area forecast discussion
National Weather Service San Francisco Bay area
351 am PST Thu Feb 22 2018
Synopsis...a weak weather system will impact the area today
bringing widely scattered showers, a slight chance of
thunderstorms in the afternoon, and lowering snow levels. This
system will also bring gusty winds and colder temperatures by
Friday morning. Dry weather and slightly warmer temperatures are
expected for the weekend. Cooler, unsettled weather to return
early next week.
Discussion...as of 3:13 am PST Thursday...kmux radar is already
showing some weak echoes over the coastal waters off of the San
Mateo coast in advance of an approaching low pressure system
approaching the area from the north. This system is not expected
to have much moisture to work with as it comes from Canada. Thus,
only scattered showers are expected to occur this afternoon and
evening with a few hundredths of an inch to around 0.15 total,
and the bulk of that expected over the Santa lucias. With the cold
air, a slight chance of thunderstorms is possible this afternoon
and evening, mainly over the north and East Bay interior. Snow
levels are forecast to drop to under 2000 feet by this afternoon
with only a dusting of snow expected at higher elevations. Showers
are expected to end overnight.
Winds are also expected to ramp up by this afternoon with this
system. Northwest winds are forecast to gust as high as 40 mph
along the coast and in the hills, and locally higher in the Winder
locations. Breezy conditions will persist into the early evening
and then winds will subside overnight.
The cold air with this trough will result in chilly overnight low
temperatures. Look for temperatures to drop to freezing, or
slightly below, across inland areas by Friday morning, with
similar readings possible again by Saturday morning. Dry
conditions and cool conditions are forecast over the weekend. Cool
and unsettled weather is expected to continue into next week.
Medium range models bring a better chance of rain to the area
early in the week with another possible system later in the week.
Aviation...as of 3:51 am PST Thursday for 12z tafs...VFR
conditions are generally expected to prevail this morning and
afternoon at San Francisco Bay and Monterey Bay area terminals.
Have seen some temporary MVFR ceilings reported around ksfo this
just prior to the 12z taf issuance. Could see some tempo
scattered/bkn030 at the terminal through sunrise, but think the broken/overcast
decks will remain above 3000 ft. Strong west to northwest winds
will develop through the day at the terminals, with sustained
winds ranging from 15 to 25 kt, and gusts over 30 kt possible
(with locally higher gusts).
Vicinity of ksfo...expect mostly VFR conditions today, though
can't rule out temporary MVFR ceilings through about 14 or 15z
this morning. Think most likely scenario this morning will see
broken/overcast decks around 3-4k ft agl, with scattered/broken decks around 4-5k
ft after mid-morning. Strong west winds will develop through the
day, increasing to around 20 kt sustained by midday, and near 30
kt by mid/late afternoon. Gusts around 35 kt seem quite likely.
Will closely monitor and amend as necessary, particularly as gusts
approach Airport weather warning criteria.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR. Scattered clouds developing Thursday
morning with brief showers possible, particularly at kmry. Strong
onshore winds will develop in the afternoon with sustained winds
around 20 kt at kmry and 25 kt at ksns, and gusts approaching 30
Marine...as of 03:38 am PST Thursday...northerly winds will
continue to increase over the coastal waters through the day as an
upper-level disturbance passes over the region. This will result
in gale-force winds in the outer waters. The strong winds will
bring steep fresh swell and hazardous seas.
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm until 1 PM
glw...pt Arena to Pigeon pt 10-60 nm from 1 PM
Small Craft Advisory...mry Bay from 9 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 9 am
Small Craft Advisory...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...sf Bay
Public forecast: Sims
Visit US at www.Weather.Gov/sanfrancisco