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

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FXUS66 KMTR 230438
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
938 PM PDT Sun Oct 22 2017

.SYNOPSIS...Warm to hot temperatures are likely on Monday and
Tuesday afternoons. Along with the heat, dry conditions will
persist through the first half of the week as a result of weak
offshore winds. A gradual cooling trend is then forecast during
the second half of the week, yet temperatures will remain above
seasonal averages.

&&

.DISCUSSION...as of 8:53 PM PDT Sunday...No forecast updates this
evening. Skies are clear as dry offshore winds develop over the
region. Northerly gradient down the coast is 6.4 mb and building
while the sfo-wmc is currently only 5 mb and forecast to
strengthen significantly the next 24 hours. Ft Ord Profiler shows
persistent northeast wind flow through the boundary layer already.
Some of our sensors up in the hills still hovering around 70
degrees at this hour with Mt Diablo now picking up 35 mph
northerly wind gusts. Stage is set for a sunny and warm Monday and
likely even warmer on Tuesday. Records could be set or tied both
days across the region. Offshore flow may weaken some by Wednesday
but any cooling looks minor at best. Saving grace will be the dry
airmass and long autumn nights that should allow for natural air
conditioning and night time relief to cool down buildings.

West coast ridge looks to stay in place through the week and into
next weekend. Things looking dry through at least Halloween.
Updated Fire weather section below as well.

&&

.PREV DISCUSSION...as of 01:47 PM PDT Sunday...High pressure continues
to build in over the region from the south and will strengthen
through midweek. As the air mass aloft warms, surface temperatures
will also increase with afternoon highs reaching 15 to 20 deg F
above seasonal averages on Monday and Tuesday. This combined with
weak offshore flow will result in temperatures reaching into the
80s at the coast with lower/middle 90s inland. With this event,
the warmest temperatures are forecast to occur on Tuesday across
the Central Coast where the warmest and driest air mass will be in
place. Cannot rule out a few of the warmest inland areas such as
Pinnacles National Park reaching into the upper 90s.

Overall, winds are forecast to remain light for most urban locations
but may become breezy and locally gusty at times in the peaks and
ridges beginning tonight before gradually tapering off Monday night
into Tuesday. These conditions will raise fire weather concerns to
some extent, but rainfall late last week is providing some temporary
relief, at least initially. By the time conditions dry out late
Monday and Tuesday, wind speeds are forecast to be weaker.

Heat risks will also increase into the moderate category both Monday
and Tuesday afternoon, mainly from the Santa Cruz Mountains southward
through the Central Coast. However, longer nights and modest
overnight cooling under clear skies will limit the overall heat
risks region-wide through this heat event. Thus, folks are urged to
remain vigilant and use extra caution during the peak heating of the
day through early this week.

The mid/upper level ridge is then forecast to weaken and shift back
offshore by midweek in response to an upper level trough digging
southward across the Great Basin and Central Plains. This will allow
for a cooling trend from Wednesday through at least Friday, yet
temperatures are forecast to remain above seasonal averages. In
addition, medium to longer range models maintain dry weather
conditions and near to slightly above average temperatures heading
through the end of October.

&&

.AVIATION...As of 9:38 PM PDT Sunday...High confidence VFR in
offshore flow through Monday night. Increasing air mass stability
under an amplifying mid to upper level thermal and height ridge
will result in surface winds tending to decouple from increasingly
gusty NE winds aloft in the Bay Area hills and mountains tonight
into Monday morning; low level wind shear is possible due to 925
mb NE winds reaching 25-35 knots based on NAM/WRF output. Warming
due to large scale air mass compression is seen on the profiler
data from Bodega Bay to Fort Ord with shallow inversions based at
sea level to 500 feet.

Vicinity of KSFO...VFR. W-NW winds this evening shifting to light
NE tonight. Low level wind shear 06z-17z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Light E-SE winds this evening into
Monday except SE winds becoming increasingly gusty in the Salinas
Valley very late tonight through Monday morning.

&&

.FIRE WEATHER...As of 8:53 PM PDT Sunday...Watching for
developing northerly winds overnight. 00z KOAK sounding showed
inversion height around 3000 feet and currently think it will be
hard to get strong winds to mix below that. Mt Diablo is currently
running sustained at around 33 mph at 3849 feet. Looked at
updated fuels and the 10 hour fine fuels are around 8-10% but
expected to climb overnight. Latest live/dead/large fuel analysis
shows fuel dryness took a pretty good plunge after the Thursday
night frontal/rain event. Upshot is will be watching winds in the
hills closely tonight. Warm and dry weather Monday will be of
concern for possible new starts or continued mop-up operations of
incidents that are wrapping up. Little or no humidity recovery
Monday night into Tuesday morning with continued light to moderate
offshore winds, followed by near record breaking heat Tuesday
afternoon. Temps to stay above normal for much of this week with
dry conditions and continued periods of offshore winds. Long range
models remain dry through Halloween and beyond.

&&

.MARINE...as of 9:26 PM PDT Sunday...Strong surface high pressure
over the eastern Pacific will build into the Great Basin early to
mid week. Gusty northwesterly winds over the coastal waters will
dissipate once the northerly pressure gradient relaxes which right
now appears to be late Monday at the earliest. A strengthening
offshore wind flow pattern will tend to push the California
interior surface based thermal trough westward to the coastline,
easing surface winds over most of the coastal waters to lighter
speeds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm

&&

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: Canepa
FIRE WEATHER: RWW

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