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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMTR 171352
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
552 AM PST Mon Feb 17 2020

.SYNOPSIS...Offshore flow will develop over the region today brining
slightly warmer afternoon temperatures and cooler overnight
conditions. Overall, expect dry and mild conditions to persist
through the week with only slight chances of light precipitation
late in the week and into the upcoming weekend.

&&

.DISCUSSION...as of 02:58 AM PST Monday...Moist onshore flow has
resulted in more widespread stratus this morning developing along
the coast and into the interior valleys. Patchy fog is even being
reported across the interior valleys this morning with visibility
falling to 1/4 mile at times. Meanwhile, high level clouds are
also advecting inland across the region with surface temperatures
generally in the middle 40s to lower 50s. While low clouds and/or
fog may become a bit more widespread through sunrise, dying is
likely to occur by midday as offshore flow develops inland. By
this afternoon, breezy northerly winds are forecast to develop in
the hills and higher elevations across the region. Gusts of 30 mph
will be likely in the hills/ridges and up to 40 mph in the peaks
while only isolated gusts are expected in the lower elevations.
This pattern will also allow for slightly warmer temperatures
region-wide this afternoon with middle 60s to lower 70s likely.

The weak offshore pattern is likely to continue into Tuesday as a
ridge of high pressure persists offshore. This will result in
another day of above average temperatures region-wide Tuesday
afternoon. However, under clear sky conditions, overnight
temperatures will trend cooler the next few nights with middle to
upper 30s likely across the interior with lower 40s elsewhere.

Offshore flow will diminish by midweek, yet continued dry weather
conditions along with temperatures above seasonal averages will
persist through the remainder of the week. Forecast model guidance
continues to indicate a mid/upper level cut-off low will approach
central or southern California late in the week. While the NBM
maintains dry conditions over our region, the operational GFS and
ECMWF both indicate the potential for isolated showers over at least
a portion of the region on Friday. Regardless, if any precipitation
does occur, rainfall amounts will be very light and likely isolated.
Something worth monitoring at least in the coming days.

Ensemble members and the NBM indicate another chance of light
precipitation over the region late in the upcoming weekend as a
system drops in from the northwest. However, operational models
continue to trend drier with this system as well as the system will
have a limited moisture tap. Regardless, chances for widespread
beneficial rainfall appear unlikely during the next 7 days.

&&

.AVIATION...as of 5:52 AM PST Monday update...Some clearing in
the high clouds is allowing for a better surface snapshot on
infrared satellite imagery. OAK visibility has dropped to 1/2SM
over the past hour or so. The GOES-West nighttime fog product
shows fog in the City of San Francisco, extending south/southeast
through the San Francisco Bay to the San Mateo Bridge. CalTrans
webcams do confirm the limited visibilities on eastern side of the
San Mateo Bridge. SFO ASOS remains VFR at the present; however,
the light northeast flow has advected the fog within 5 statute
miles of the terminal. Have gone ahead and amended the SFO TAF to
take into account the latest satellite analysis and trends.

Vicinity of KSFO...updated at 5:52 AM PST...VFR at the present
with low clouds/fog approaching the terminal from the N/NE,
according to GOES-West nighttime fog product. This fog bank will
bringing an increased chance of observing decreased visibilities
at the terminal within the next few hours.

SFO Bridge Approach...updated at 5:52 AM PST...Nighttime fog
product shows fog impacting the eastern half of the San Mateo
Bridge at the present, confirmed with CalTrans webcams. With N/NE
flow, will likely see the fog expand southwestward over the next
few hours.

Monterey Bay Terminals...Low clouds have mixed-out around the
Monterey Peninsula over the last few hours with VFR conditions
returning to MRY. Could see low clouds try to redevelop over the
next several hours at MRY. Meanwhile at SNS, infrared satellite
imagery shows valley stratus/fog developing in the Salinas Valley,
already within the vicinity of SNS as of the 12Z TAF publication
time. Expect to see stratus expand in the Salinas Valley over the
next few hours.

&&

.MARINE...as of 02:58 AM PST Monday...Light to moderate north to
northwest winds will persist over the coastal waters during the
day on Monday. Areas of gusty winds and wave heights greater than
10 feet will create hazardous seas for small crafts over parts of
the waters. A series of northwest swells will continue through the
forecast period.

&&

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

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Rowe
MARINE: Rowe

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.