Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 180540
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1040 PM PDT Thu Oct 17 2019

.SYNOPSIS...Cooler and breezy conditions will continue this
evening in the wake of a frontal passage. Another weak front will
move through Friday night bringing more breezy winds to the area
along with some possible showers to the North Bay. A warming and
drying trend will then develop late this weekend and into early
next week.

&&

.DISCUSSION...as of 8:45 PM PDT Thursday...Mostly clear skies
continue as the marine layer has mixed out behind the passage of a
weak cold front. Gusty winds developed across the region this
afternoon, but have begun to ease for most locations. Winds will
continue to diminish tonight, but will remain somewhat breezy
over the waters and near the coast. At its peak, many areas saw
wind gusts of 30 to 35 mph with the San Francisco Airport
recording a wind gust of 41 mph earlier this evening. Current
temperatures are within a few degrees of this time yesterday with
most sites in the upper 50s to low 60s. Expect some chillier
overnight lows compared to this morning given clearer nighttime
conditions. Lows will mainly be in the mid to upper 40s with low
50s around the SF Bay. Isolated valley locations will dip into the
upper 30s.

Similar, but less breezy, conditions are forecast for tomorrow
with highs along the coast in the 60s and low to mid 70s inland.
Another weak system will move across the North Bay late Friday
night and into Saturday morning. This will bring a slight chance
of some light showers to the North Bay early Saturday morning with
conditions expected to remain dry elsewhere. Any resulting
precipitation would be fairly minimal. Behind the front localized
dry offshore winds will develop over the Santa Lucia Mountains
Friday night (see Fire Discussion). As the system moves eastward,
a brief period of dry offshore winds will be possible over the
North Bay late Sunday night into early Monday. However, these
winds are not forecast to be strong.

Gradual warming will begin on Sunday as high pressure builds over
the eastern Pacific with more robust warming and drying then
expected early to mid next week. A strong upper ridge is progged
to strengthen over the eastern Pacific early next week and move
towards northern California and the Pacific Northwest into late
week. At the same time, models show surface high pressure moving
into the Pacific Northwest with low pressure developing along the
California coast. This could indicate a more widespread offshore
flow event into late next week (see Fire Discussion).
Additionally, models show 850 mb temperatures up to or just over
20 deg C across the region around this time bringing back
widespread above normal temperatures. This is still fairly far out
in the forecast and conditions will continue to be monitored in
the coming days.

&&

.AVIATION...as of 10:42 PM PDT Thursday...The marine layer has
mixed out following the frontal passage. VFR conditions expected
all areas through Friday. Winds have decreased this evening after
peak gusts to near 35 kt at SFO earlier.

Vicinity of KSFO...VFR. West winds to 15 kt gusting to 20-22 kt
through 12Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR.

&&

.FIRE WEATHER...As of 02:12 PM PDT Thursday...Short term fire
weather concerns will be focused over the southern portion of the
district with weak to moderate offshore flow (NE winds at 925mb)
Friday night/early Saturday. Local WRF model highlights NE winds
over the Santa Lucia Mts with NE winds 25-35 mph with humidity
recovery pretty poor. Offshore flow weakens through the day on Saturday
with increasing RH. Longer term fire weather concerns then switch
large scale with more widespread offshore flow. Models build large
scale high pressure aloft over the region and EPAC. At the
surface, high pressure moves into the PacNW with low pressure
along the coast setting the stage for offshore. The peak offshore
period appears to be Tuesday night/Wednesday. The GFS shows a
SFO-WMC gradient of 14.9mb, which is pretty solid and would likely
result in a Fire Watch/Red Flag. A lot will change between now and
then, but something to keep an eye next Tuesday through Thursday.

&&

.MARINE...as of 10:36 PM PDT Thursday...High pressure off the
central California coast will keep gusty northwest winds over the
southern waters through Saturday. Winds will be lighter over the
northern waters. A frontal system will pass north of the area on
Sunday with high pressure building northward behind the front.
This will increase the northwest winds over the northern waters
early next week. Large northwest swells  will peak late tonight
and Friday before slowly subsiding Friday night.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...High Surf Advisory...CAZ006-505-509-529-530
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Rough Bar Advisory for SF Bar
             SCA...Mry Bay

&&

$$

PUBLIC FORECAST: AS/Sims
AVIATION: W Pi
MARINE: W Pi
FIRE WEATHER: MM

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