163
FXUS66 KMTR 160504
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
904 PM PST Wed Jan 15 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1256 PM PST Wed Jan 15 2025

Very quiet once again today, as will be the case through this
weekend. Potential for some local fog early this weekend around
coastal areas, and the potential for offshore winds early next
week.

&&

.UPDATE...
Issued at 902 PM PST Wed Jan 15 2025

Offshore pressure gradients, easterly winds, dry continental weather
largely prevails, the WMC-SFO 8.8 mb gradient is strongest, while
SAC-SFO is 0.4 mb and ACV-SFO is 0.9 mb. The late afternoon 00z
Oakland upper air sounding showed 0.39" precipitable water which
is below mid January normal and in the 25th percentile. Satellite
shows a clear sky, post sunset outgoing longwave radiational
cooling is well underway and will continue to daybreak Thursday. A
frost advisory was issued for 1 am to 9 am Thursday for the
southern interior zones.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 1256 PM PST Wed Jan 15 2025

Absolutely gorgeous day today under clear skies and very little
wind. A slight offshore gradient still exists where the mean flow is
easterly due to lingering high pressure over the Great Basin and a
nearly stationary upper low well off the coast of Baja. This pattern
continues tomorrow before the upper low finally starts to move
inland.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 1256 PM PST Wed Jan 15 2025

A look at the long term period provides a bit more to talk about and
an frustrating level of uncertainty. Once the aforementioned upper
low moves inland, a broad upper ridge develops over the West Coast
and largely remains in place through the extended period. The
biggest question mark right now is how much a deep trough will dig
into the central US, whether or not a new cut off low will develop
from it in the Desert SW, and how strong that cut off low may be. As
it stands currently, there is considerable uncertainty in an
offshore wind event late this weekend and early next week. High
confidence that we will not see any rain, and the ridge will
dominate the pattern, but low confidence on if we will see impactful
offshore winds or not. Per latest hi-res WRF ensemble guidance,
there is a bimodal distribution after this weekend regarding the
strength of the SFO-WMC (San Francisco to Winnemucca, NV)
pressure gradient. Nearly half of ensemble members advertise a
neutral or slightly onshore gradient, whereas the other half of
members advertise an offshore gradient near the 90th percentile,
which means the potential for moderate offshore winds. Likewise,
if we zoom out to larger scale global models which include more
ensemble members, there is nearly an even distribution of
solutions varying from basically light wind and fair weather to
moderate offshore winds. Based on the lack of rain in the forecast
and the fact that the Energy Release Component of grasses and
shrubbery in the Central Coast is nearing the 80th percentile, we
will begin increasing messaging regarding the potential for at
least some fire weather impacts for southern areas next week.
However, based on the large amount of uncertainty, it would be
wise to pay close attention and stay up to date with the forecast
for the latest information.

&&

.AVIATION...
(06Z TAFS)
Issued at 904 PM PST Wed Jan 15 2025

|
Mostly VFR through the night aside from the North Bay which will see
some pockets of fog into early Thursday. Winds stay light to
moderate with local effects driving most of the wind directions
through much of the TAF period. Winds around the Monterey Bay will
be slightly more unified as overnight southeast drainage winds
affect the area and last through much of Thursday morning. Lower
clouds build over the ocean and move inland into Thursday night.
Filling over HAF, then the Monterey Bay and SF Bay terminals, and
becoming widespread into Friday morning with some reductions in
visibility.


Vicinity of SFO...VFR through late Thursday night. Winds stay light
and variable through mid Thursday afternoon before moderate
northwest winds arrive. Winds reduce late Thursday night as IFR CIGs
build around the SF Bay.


SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through late Thursday night. Expect
light winds through the late night, with moderate southeast drainage
winds arriving in the late night. These winds linger through the
morning before MRY turns light and variable, and more moderate
northwest winds affect SNS into the mid afternoon. Winds turn light
into Thursday night as IFR CIGs fill over the terminals with some
reduced visibility.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 904 PM PST Wed Jan 15 2025

Winds stay light through the night but become more northerly
across the waters. Northerly winds increase on Friday will result
in a modest building of seas for the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory from 1 AM to 9 AM PST Thursday for CAZ516>518.

PZ...None.
&&

$$

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...Murdock
MARINE...Murdock

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