527
FXUS66 KMTR 140511
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
911 PM PST Mon Jan 13 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 749 PM PST Mon Jan 13 2025

Cold and frosty conditions are anticipated through at least mid-
week across the Bay Area and Central Coast. Temperatures overall
will moderate some with little to no opportunities for widespread
rainfall.

&&

.UPDATE...
Issued at 749 PM PST Mon Jan 13 2025

The overall short term forecast remains in good shape with just a
few tweaks to MinT for tonight. Satellite imagery reveals
intermittent high clouds spilling over top of the elongated ridge
axis that stretches from the Eastern Pacific up through portions
of the Pacific Northwest. The northeasterly flow aloft will
support the transport of thin veils of cirrus through the
overnight time period. With a few days of moderate offshore flow,
the boundary layer has dried. In fact our 00Z sounding from the
Oakland Airport reveals a precipitable water value, a good proxy
for total column moisture, is in the lowest 10th percentile with
a value of around 0.22". With the pressure gradient between
coastal California and the Great Basin easing, we`ve seen our
offshore flow relax. With mostly clear skies, diminishing winds,
and a dry airmass, the stage will be set for largely ideal
radiational cooling. If upper cloud cover is a bit more dense than
currently anticipated, outgoing longwave radiation may not be
optimized and overnight temperatures may remain above what is
projected. Still, across the Central Coast and East Bay Interior,
temperatures and dewpoints are running about 2-5 degrees lower
than this time yesterday. This should allow temperatures in these
areas to fall a little lower than this morning and overnight MinT
grids have been adjusted to reflect this. Lows across the extreme
southern Salinas Valley may fall down to around 25 degrees, with
most areas in the mid to upper 30s. This should easily support the
formation of patchy to in some spots widespread frost and
increase the risk for cold related hazards for people/pets and
infrastructure without adequate warmth. While consideration was
given for a small Freeze Warning across the extreme southern
Salinas Valley, we`ll opt to maintain the Frost Advisory and
continue our messaging via other means.

Otherwise, the remainder of the forecast remains unchanged.

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 128 PM PST Mon Jan 13 2025

Clear skies and cool temps abound under a dry airmass and weak
offshore flow. A weak closed upper low off the coast of SoCal moved
through this morning, leading to a brief period of gusty winds that
are still lingering in some areas, but are easing through midday. As
such, the Wind Advisory has been cancelled, and is no longer in
effect. Not really much else to talk about for the daytime today.
Chilly overnight temperatures will be the story again tonight with
temps in the mid-to-upper 30s across most interior areas, and even
some coastal areas such as Santa Cruz and the Monterey Bay area. A
Frost Advisory has been issued for all of the interior North Bay,
Bay Area, and Central Coast, as well as the Monterey Bay coastal
areas for tonight until 9 AM Tuesday morning.

Regarding smoke in the sky; you may notice a slightly more reddish
hue to the sunset this evening thanks to some very light smoke
concentration from some burning up in Canada, as well as the SoCal
fires. This smoke is not expected to cause any issues since it
will mostly be aloft and will be drifting out over the waters.

&&

.LONG TERM...
(Tuesday night through next Sunday)
Issued at 128 PM PST Mon Jan 13 2025

Quite a quiet pattern with quite the signal for no rain in quite a
while. Make sense? Good. (coffee-fueled meteorologist brain fog
enters the chat)

Longwave ridging over the northeast Pacific and Gulf of Alaska with
a few embedded shortwaves dominates the West Coast pattern through
the next seven days. However, none of these cold-core shortwave
troughs will be deep enough to overcome the broad ridge pattern that
will eventually envelope the West Coast by mid-to-late this week.
These shortwaves feed into a deeper upper low out of the Hudson Bay,
promoting a very cold setup much of the rest of the US. However,
this also promotes a highly amplified ridge over the West Coast
which appears to remain stagnant through much of the last half of
the month as the Hudson Bay low persists. Unfortunately for us, this
means there is very little to no chance of rain for the second half
of January. The good news is that most of the Bay Area, and the
North Bay especially, have seen decent rain so far this year, so
fuel indices in regard to fire weather will take some time to
respond. Central Coast fuels are more on the drier side and will
dry out more quickly though. Will certainly be something to keep
an eye on through these next couple of weeks.

&&

.AVIATION...
(06Z TAFS)
Issued at 911 PM PST Mon Jan 13 2025

High confidence of VFR through the TAF period. Light and variable
winds overnight into Tuesday morning. Some light onshore flow
develops on Tuesday afternoon at the immediate coast, with offshore
flow continuing in the interior.

Vicinity of SFO... VFR through the TAF period. Breezy north-
northwest flow is expected to continue into the early morning hours.
Winds become light on Tuesday morning before breezy onshore flow
resumes in the afternoon.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR with valley drainage winds overnight.
Winds shift onshore late Tuesday morning, remaining light to
breezy.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 911 PM PST Mon Jan 13 2025

Generally weak winds will persist through much of the week as high
pressure remains over the region. Wave heights will also remain
relatively low, generally between 4 and 7 feet. Northwest winds
will build as well as wave heights late in the week and into the
upcoming weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory from 1 AM to 9 AM PST Tuesday for CAZ504-506-510-
     512>518-528>530.

PZ...None.
&&

$$

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...DialH
MARINE...DialH

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