899
FXUS66 KMTR 131755
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
955 AM PST Mon Jan 13 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1215 AM PST Mon Jan 13 2025

Dry conditions continue this week with mostly clear skies, some
gusty offshore winds, and chilly mornings.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1215 AM PST Mon Jan 13 2025

Believe it or not, the pattern is changing tonight. A short wave
trough at 500 mb is moving through the Bay Area, bringing a patch
of mid to high level clouds. Over the next 24 hours, this feature
will continue to dive south, and become cut-off roughly 500 miles
west of northern Baja. At the same time, a ridge from the Eastern
Pacific subtropical high will slide over the top, towards the
Pacific Northwest. This will create a situation with high pressure
directly north of low pressure, or a Rex Block.

With lighter winds, the temperatures are dropping more efficiently
tonight. The mid to high level clouds will put a damper on the
cooling, but only briefly. The Satellite loop shows we will only
be dealing with these clouds for a couple hours before the clear
skies return.

This pattern will also support another round of strong offshore
winds through Tuesday, but not quite as widespread or as strong as
the recent wind advisory. Winds will calm by mid-week as the cut-
off low gradually fills in the absences of any upper level
support.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 1215 AM PST Mon Jan 13 2025

The new Rex Block pattern will live up to its name, keeping the
weather consistent through the week. The skies will stay mostly clear
with no chance of rain. Offshore winds will persist through mid-
week, with decreasing intensity. The 850 mb temperature will
remain between the 50th and 75th percentile for this time of
year. The clear skies and dry air mass will enhance radiational
cooling at night. Minimum temperatures will range from the mid 30s
inland to mid 40s near the coast. Maximum temperatures will be in
the low to mid 60s for most.

By Friday, the pattern will begin to break down as the low west of
Baja gets reabsorbed into a trough moving through the desert SW.
This will allow a return to the Omega Block pattern that we had
all of last week. This Omega Block - Rex Block - Omega Block
combination is bringing unusually dry weather to what is
typically the wettest time of the year. Downtown San Francisco has
only recorded 0.19" of precipitation so far in January, when the
normal for the first 2 weeks is over 2". The extended guidance and
CPC outlooks suggests there is a good chance this next omega
block keeps us dry through the following week and possibly all the
way to the end of the month.

With the fires in Los Angeles and the prolonged dry spell here,
we are starting to take a peek at fuel moisture. The energy
release components have responded quickly to this weather, and are
well above normal for this time of year. Fortunately, we entered
the month in a much better place than southern California, and
nearly all zones are still below the 60th percentile for the
annual average. The Central Coast zone is the exception, as the
ERC has recently crossed the 60th percentile and is expected to
reach the 80th over the next week. For the first time in months,
the Southern California Geographic Area Coordination Center has
placed the Central Coast Zone (coastal Monterey County) in a low
risk of significant fire potential starting Sunday and continuing
through the end of the forecast (Saturday). The rest of our area
remains in the "little to no risk" category this week.

&&

.AVIATION...
(18Z TAFS)
Issued at 954 AM PST Mon Jan 13 2025

VFR through the TAF period. Periods of gusty winds will persist
through early morning across the Bay Area terminals before easing by
this afternoon and especially so this evening. The threat of LLWS
across the North Bay has diminished as well. Winds will be
light/variable into the night and even into Tuesday morning.

Vicinity of SFO...VFR through the TAF period. Breezy to gusty
northeast winds will affect the SF Bay through the morning and into
the afternoon before winds ease. Winds become light/variable into
Tuesday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the TAF period. Light/variable
winds this morning for MRY and southerly for SNS. They will become
onshore this afternoon for a brief period. Southeast drainage winds
build into early Tuesday morning for SNS.

&&

.MARINE...
(Today through Saturday)
Issued at 954 AM PST Mon Jan 13 2025

Gale force gusts linger in the northern outer waters early this
morning with other areas seeing breezy to gusty winds lasting
through the afternoon. Hazardous conditions for small crafts will
persist through the midday with elevated wave heights between 9
to 13 feet expected. Winds ease and seas subside into the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 1 PM PST this afternoon for CAZ006-
     506-508.

     Wind Advisory until 10 AM PST Tuesday for CAZ504.

PZ...Small Craft Advisory until 3 PM PST this afternoon for Pigeon Pt
     to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena
     to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N
     of Bay Bridge.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...RGass
MARINE...RGass

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