830
FXUS66 KMTR 120915
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
115 AM PST Sun Jan 12 2025

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 1209 AM PST Sun Jan 12 2025

Continued dry weather this week with chilly mornings and mostly clear
skies.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1209 AM PST Sun Jan 12 2025

The atmosphere is very dry. The 00Z sounding found a 0.15" PWAT.
That`s in the bottom 0.2% across 56,000 weather balloon launches
going back to 1948. While there`s no direct reason to discuss the
LCL on this cloudless night, the high temperature and low dew
point are demonstrated by the 3353m surface based LCL, which is
89m higher the previous record for the month of January
(1/20/1963). With this exceptionally dry air mass, there isn`t a
cloud in the sky anywhere over California. The dry air and clear
skies will allow much more efficient radiative heat loss
overnight, and temperatures are generally dropping much faster
than last night. The temperatures are a bit of a mixed bag
however, with some downsloping flow keeping some areas warmer (and
drier) for longer. A good example is Napa, where it`s 54 degrees
with a dewpoint of 19F, compared to Santa Rosa, where it`s 39
degrees with a dewpoint of 37F. I reverted the temperature
forecast back to the standard NBM, but since it`s so sensitive to
wind direction, the uncertainty is high even for the minimum
temperatures this morning. Nevertheless, it will be a chilly start
for most. Winds are still strong across higher elevations,
especially in the North Bay. We are continuing to rely heavily on
the local WRF winds in the official forecast, which suggests the
10 AM expiration time on the Wind Advisory is appropriate for all
but the North Bay Mountains, where winds will likely pick up to
advisory level Sunday evening, and persist through the day Monday.
Otherwise, Sunday will be another very nice day with comfortable
afternoon temperatures generally in the 60s, and plenty of
sunshine.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 1209 AM PST Sun Jan 12 2025

On Monday, a fast moving short wave trough will move from N to S
across California, eventually becoming cut-off west of Southern
California. This will transform the pattern from an Omega block
to a Rex block (high pressure north of low pressure), which will
be with us through the majority of the week. While there is some
discrepancy in the ensemble clusters, the most likely outcome is
that the low will eventually dissipate or perhaps hitch a ride to
the East, as the ridge retreats back to the Eastern Pacific. In
other words a return to a very stable Omega blocking pattern by
next weekend. All this means that there is still no rain in the
official forecast through the 18th and the global ensembles show
this dry period has a 90% chance to extend through the 25th and
likely beyond. The pattern this week will also support some
offshore winds, though the strength should decrease substantially
by mid-week. With enhanced radiational cooling, morning
temperatures will be chilly. The 850 mb temp is hovering between
the 50th and 75th percentile, so we are not expecting wide-spread
freezing temperatures, but most inland areas will drop into the
30s before the sun comes up.

&&

.AVIATION...
(06Z TAFS)
Issued at 929 PM PST Sat Jan 11 2025

All sites VFR through TAF period, low confidence that fog will
develop at STS overnight. Winds will be light but conditions should
be dry enough to prevent fog from developing at STS overnight. A mix
of northerly to northwesterly winds continues through the TAF period
with lighter, at times variable, winds expected overnight. Gusts
have generally dropped off at all airports (excluding KHAF) but
isolated stronger gusts to around 15 knots remain possible for the
next few hours.

Vicinity of SFO...VFR. Moderate northerly winds continue through
tomorrow afternoon when winds shift more northwesterly and weaken
slightly.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals...VFR. Winds will shift more southeasterly at
both MRY and SNS overnight before more northwesterly flow returns
during the day. Winds become more moderate during the day but will
start to weaken and become more variable by late tomorrow evening.

&&

.MARINE...
(Tonight through next Friday)
Issued at 929 PM PST Sat Jan 11 2025

Gale force winds continue over portions of the northern outer
coastal waters, particularly the far northwest corner, with
strong,  gusty winds expected elsewhere. Hazardous conditions for
small  crafts will persist through Monday with elevated wave
heights  between 10 to 15 feet expected. Winds will gradually ease
late  Sunday into Monday as the high pressure gradient weakens
over the  Pacific Ocean. Significant wave heights will remain
elevated through  the early work week but will abate below small
craft criteria by mid  week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 6 AM this morning to noon PST today
     for CAZ006-506-508.

     Wind Advisory until 10 AM PST this morning for CAZ504-512-514-
     515.

     Frost Advisory until 9 AM PST this morning for CAZ516-518.

PZ...Small Craft Advisory until 3 AM PST early this morning for Pt
     Pinos to Pt Piedras Blancas 0-10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory until 9 AM PST this morning for Pigeon Pt
     to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Reyes
     to Pigeon Pt 0-10 nm.

     Gale Warning until 3 PM PST this afternoon for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 9 AM PST Monday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Kennedy
MARINE...Kennedy

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