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fxus66 kmtr 190008 
afdmtr

Area forecast discussion
National Weather Service San Francisco Bay area
508 PM PDT Fri Oct 18 2019

Synopsis...today will be another cool day for the Bay area
before another weak front moves through late this evening. Winds
will be breezy as the front passes and there is a slight chance of
rain with minimal accumulations for the North Bay late tonight
into Saturday morning. Temperatures will gradually warm over the
weekend before a more robust warming trend early next week along
with offshore flow.

&&

Discussion...as of 1:39 PM PDT Friday...under partly cloudy
skies, afternoon temperatures are running similar to those from 24
hours ago with readings in the mid 60s to the lower 70s. Satellite
imagery shows high clouds moving across the Bay area southward, as
well as some cumulus forming over higher peaks, and coastal
stratus from Marin County south to the Monterey peninsula.

Tonight a weak frontal boundary is forecast to bring rain
chances to mainly the North Bay overnight and into Saturday
morning. Only a few hundredths of an inch at most can be expected,
and mainly in the extreme northern portions of Sonoma and Napa
counties. In addition, the passing boundary could result in an
increase in offshore flow across the Santa Lucia mountains. These
winds are not forecast to be overly strong, but with low humidity
it raises the concerns for a fire threat (see fire discussion
below).

Onshore flow will persist Saturday and Sunday under a strong
northwest flow. 500 mb heights will slowly rise for gradually
warming temps over the weekend. By Monday, the upper level ridge
will continue to grow and shift eastward towards the coast,
initiating a much more substantial warming trend expected to last
through the middle of the week. High temps should level off by
Wednesday. However, while temperatures warm into the mid to upper
80s at the surface, the wind pattern shifts by Tuesday to a more
widespread, offshore pattern, increasing the potential for
possible fire weather issues through Thursday.

&&

Aviation...as of 5:05 PM PDT Friday...moisture boundary that
brought clouds to the coast this morning are mostly dissipating
with a few cigs lingering around mry. Models indicate the lower
level drying out this evening so VFR is expected tonight. The only
possible exception is mry where clouds could reform later. Both
hi-res and NAM models bring in another batch of low level moisture
Saturday morning after 15z so will have to watch for daytime
clouds/low cigs on Saturday.

Vicinity of ksfo...VFR through Saturday morning. Models indicate
an increase in low level moisture after 15z which could bring cigs
at or below 5000 ft. West winds to 20 kt gusting to 25 kt through
04z.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...becoming VFR as clouds clear away from
the Bay. Small chance of IFR cigs reforming near mry after 05z but
if it does it will burn off early Saturday morning. Both
hi-res and NAM models bring in another batch of low level moisture
Saturday morning after 18z so will have to watch for daytime
clouds/low cigs on Saturday.



&&

Fire weather...as of 3:05 PM PDT Friday...two main fire weather
concerns over the next seven days. The first impact will be
focused tonight over the higher terrain of the Santa Lucia
mountains. Hi-res WRF model continues to show a localized
offshore flow scenario tonight with north to NE winds 25-35 mph with
poor humidity recovery. The second impact will be focused on next
week. High pressure is forecast to build starting Sunday/Monday
and continue through much of the next week with a warming and
drying trend. More importantly, offshore flow is forecast to
develop on Monday and increase each day before peaking Wednesday
night/Thursday morning. Latest GFS continues to show a robust
15mb+ sfo-wmc...that being said the European model (ecmwf) isn't as strong. None
the less, this situation next week needs watching. Even if the
strength of the wind doesn't verify relative humidity will be low by night number
three. Stay tuned....

&&

Marine...as of 04:49 PM PDT Friday...predominately light to
locally moderate northwest winds the rest of today and through the
weekend. The strongest winds will be concentrated along the Big
Sur coast. The northwest swell will peak today and then begin to
subside this evening with hazardous seas for smaller vessels
continuing into this weekend.

&&

Mtr watches/warnings/advisories...
... Surf advisory...caz006-505-509-529-530
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm until 3 am
Small Craft Advisory...rough bar advisory for sf bar until 3 am

&&

$$

Public forecast: Sims
aviation: west pi
marine: drp
fire weather: mm

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