620
FXUS66 KMTR 090839
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
139 AM PDT Mon Sep 9 2024

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

.SYNOPSIS...
Issued at 138 AM PDT Mon Sep 9 2024

Warm temperatures across the region persist into Monday, before a
deep upper level trough brings a major cooldown and breezy winds by
Tuesday and through the remainder of the week.&&

.SHORT TERM...
(Today and tonight)
Issued at 138 AM PDT Mon Sep 9 2024

Today temperatures will continue on a cooling trend as an upper
level trough begins to impact the Pacific Northwest and conditions
begin to cool aloft.  Afternoon maximum temperatures will reach the
upper 80`s to mid 90`s across the interior, low 70`s to low 80`s
around the Bayshore, and 60`s to mid 70`s near the Pacific coast. A
few of the warmest interior portions of Monterey and San Benito
counties will approach 100 degrees.

Tonight, expecting more widespread clouds to penetrate inland into
the coastal adjacent valleys as the marine layer begins to deepen.
Low temperatures will drop into the upper 40`s in the coldest
interior spots to the mid 50`s elsewhere. Areas around the Santa
Clara Valley will see temperatures in the mid-to-upper 50`s while
the hills and higher elevations only cool to the 60`s to low 70`s,
especially in the Central Coast.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 138 AM PDT Mon Sep 9 2024

A more substantial upper level trough will drop into the Pacific
Northwest by Tuesday and Wednesday. This will drop temperatures back
to near or below seasonal averages with mid 70`s to mid 80`s across
the interior and more widespread 60`s at the coast. Winds will also
increase generally out of the northwest reaching 20-30 mph in the
gaps and passes. Any precipitation with this system looks to remain
to the north with forecast guidance trending drier across our
region. Some offshore flow is possible as the low shifts across the
Intermountain West on Thursday, especially in the higher elevations.
However, it does not appear to be a great setup for stronger
offshore winds.

The 6-10 and 8-14 Day Outlooks indicates temperatures below
seasonal averages and precipitation above seasonal averages into the
third week of September.

&&

.AVIATION...
(06Z TAFS)
Issued at 1058 PM PDT Sun Sep 8 2024

Widespread IFR to LIFR CIGs expected overnight with elevated fog
potential in the North Bay and Monterey Bay region. Stratus is
starting to move inland with CIGs expected to develop between 08-10Z
for most airports. Pushed back stratus arrival time by a few hours
for most Bay Area sites from 00Z TAFs to better reflect current
positioning of stratus on Night Fog and ensemble guidance/LAMP
probability plots. Stratus is expected to clear out between 16-18Z
for most sites but may clear out slightly later over the Monterey
Bay region where patchy dense fog has developed to past few nights.
Stratus is expected to return late tomorrow for most sites.
Northwest winds weaken overnight, becoming locally variable, before
more moderate northwest winds return during the day tomorrow.

Vicinity of SFO...VFR becoming IFR overnight. Night Fog shows
stratus located over the western portions of the SF peninsula and is
expected to reach SFO later tonight between 09-12Z. The marine layer
has deepened slightly compared to the last few days which is
increasing confidence in an earlier return of stratus to SFO. CIGs
will clear out by late morning with VFR conditions persisting
through the afternoon/evening before stratus returns overnight.
Moderate northwest winds persist through the period with gusts up to
25 knots possible tomorrow afternoon/evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Widespread stratus and LIFR CIGs currently
impacting MRY and SNS. Patchy dense fog is again expected to develop
overnight/during the early morning which will at least temporarily
reduce visibilities to less than 1SM at both airports. Low to
moderate confidence that CIGs will clear between 18-20Z. Notably the
NBM, HRRR, and LAMP models are suggesting MRY will stay socked in
through the entire TAF period. This scenario cannot be entirely
ruled out but for now current thinking is CIGs will temporarily
scatter out at MRY around 20Z with an early return of stratus at
02Z. Light to moderate northwest winds persist through the TAF
period with locally variable winds possible during the early morning
hours.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 1058 PM PDT Sun Sep 8 2024

Light north to northwesterly winds will prevail through Monday
with occasionally gusty winds over the southern waters. Winds will
gradually ramp up on Tuesday as an upper level low pressure
system approaches from the north. This system will swing across
the region midweek bringing moderate and gusty north to
northwesterly winds and higher wave heights across the coastal
waters. Unsettled conditions will continue through the end of the
week as a second upper level low arrives next weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Kennedy
MARINE...CW

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NWS MTR Office Area Forecast Discussion