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

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000
FXUS66 KMTR 141059
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
259 AM PST Thu Dec 14 2017

.SYNOPSIS...Dry weather continues this week as high pressure resides
over California. A mainly dry cold front will sweep south over
the area late Friday night and early Saturday morning which then
increases N-NE winds along the ridges and peaks Saturday. A dry
pattern may turn to a wet weather pattern next week.

&&

.DISCUSSION...as of 2:56 AM PST Thursday...After an extended
period of stagnant weather with a Rex Block, a pattern change is
likely this weekend and possibly rain returning next week.

Currently a stout offshore flow set up prevails with high pressure
over the Great Basin and low pressure along the coast. Latest
offshore gradients are actually stronger than 24 hours ago at 14
mb (SFO-WMC). Needless to say, this pressure gradient is leading
to mild temperatures, dry conditions and very gusty winds over
higher elevations. Mt Diablo is once again the winner for
strongest winds with gusts up to 53 mph. Santa Rita Peak in San
Benito County is the driest with relative humidity values sitting
about 10%. For what it`s worth, that is up about 5% from earlier
in the night. Heightened fire weather concerns exist over the
peaks tonight. Similar to last night, different story in the
valleys with much weaker winds and colder temperatures. Several
interior valleys locations are currently sitting in the upper 20s
to lower 30s. Patchy frost will be possible in these locations. A
few stations across the North Bay Valleys are also reporting dense
fog.

If you liked yesterday`s weather you`ll like today`s. Mostly sunny
skies and above normal temperatures. High pressure finally breaks
down on Friday as a weak frontal boundary and associated upper
level trough sweep through the region. Models continue to show a
dry frontal passage Friday night for the Bay Area, but some light
precip is poss for far N CA. This change in the pattern will bring
slightly cooler temperatures this weekend. More importantly, it`s
the weather conditions that develop behind the front impacting the
Bay Area. Offshore flow gradients ramp up pretty quick Friday
night into Saturday morning. The local WRF model continues to
show NE winds of 20-30 mph with gusts exceeding 50 mph over the
higher terrain of the North/East Bay and Santa Cruz Mountains.
Given that it is still several forecast periods out will hold off
on a wind advisory, but issue a hazardous weather outlook to
highlight winds. In addition to the wind impact, fire weather
concerns will also develop. Humidity values will recovery early
Friday night, but plummet below 30% as NE wind kick in. Breezy to
gusty NE winds persist through Sunday morning. A fire weather
watch may be needed for Saturday night as humidity recoveries will
be poor all night with NE winds over higher terrain.

High pressure rebuilds over the region Sunday through Tuesday. The
much talked about precipitation chances for the middle of next
week still exist. In fact, the 00Z models are much different than
24 hours ago. The big three models all show a large scale trough
sweeping through the West Coast on Wednesday. All three models
also show some QPF around the Bay Area as well. It`s still too far
out for exact amounts, but at this point we`ll take anything we
can get. Hope the models stay locked on this solution and don`t
flip flop back to drier solutions.

&&

.AVIATION...As of 10:00 PM PST Wednesday...A few low clouds are
appearing along the coast. Clouds should stay out of the SFO Bay
Area tonight as surface high pressure is still quite prominent
over the Great Basin and the pressure gradients will be strongly
offshore. The exception is KSTS where fog will likely develop
again overnight.

Vicinity of KSFO...VFR.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Southeast winds to 10 kt in the
Salinas Valley early Thursday morning.

&&

.CLIMATE...

Record high temperatures for Thursday, December 14, 2017.

SF BAY AREA                     December 14
.LOCATION................
 HEALDSBURG..............       77/1942
 SANTA ROSA..............       72/1956
 KENTFIELD...............       70/1942
 SAN RAFAEL..............       70/1959
 NAPA....................       73/1959
 SAN FRANCISCO...........       69/1988
 SFO AIRPORT.............       69/1958
 OAKLAND AIRPORT.........       65/1958
 RICHMOND................       67/1983
 LIVERMORE...............       75/1958
 MOFFETT FIELD...........       72/1958
 SAN JOSE................       73/1958
 GILROY..................       72/1988

MONTEREY BAY AREA
.LOCATION................
 MONTEREY................       78/1953
 SANTA CRUZ..............       82/1953
 SALINAS.................       80/1988
 SALINAS AIRPORT.........       81/1953
 KING CITY...............       83/1958

&&

.MARINE...as of 09:56 PM PST Wednesday...Winds will become
northwest as high pressure over the Great Basin weakens and high
pressure over the eastern Pacific strengthens.  Winds will
increase significantly Friday night after an upper  level
shortwave moves through the area.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...NONE.

&&

$$

PUBLIC FORECAST: MM
AVIATION: W Pi
MARINE: W Pi

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