042
FXUS66 KMTR 070919
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
119 AM PST Thu Nov 7 2024

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

.SYNOPSIS...
Issued at 116 AM PST Thu Nov 7 2024

A Red Flag Warning remains in effect through 7 AM today for
critically dry conditions and strong offshore flow. Fire weather
concerns ease this weekend as rainfall chances come back into the
forecast.

&&

.SHORT TERM...
(Today and tonight)
Issued at 116 AM PST Thu Nov 7 2024

A Red Flag Warning remains in effect through 7 AM today for the
interior North Bay, San Francisco Peninsula Coast, San Francisco Bay
Shoreline, and East Bay Hills due to strong offshore winds and
critically dry conditions. The SFO-WMC pressure gradient peaked at
-14.1 mb at 15Z (7 AM) Wednesday. It is currently observed at
-11.5 mb and is expected to continue this weakening trend as high
pressure over the Intermountain West weakens and coastal troughing
over the West Coast retrogrades offshore, thus weakening the surface
pressure gradient and the associated winds. There is uncertainty on
when exactly the pressure gradient will reverse to become positive
(onshore), but reasonable best case scenario (for fire weather
concerns) would be as early as Friday night. Offshore flow will
allow for critically dry conditions to persist through the day with
moderate relative humidity recovery expected in bayside, coastal,
and valley locations and poor relative humidity recovery expected in
the higher elevations. High pressure with stable air and light winds
will allow for smoke/haze from the Mountain Fire in Ventura County
to be seen across the Central Coast.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 116 AM PST Thu Nov 7 2024

The region will remain under the influence of the positively tilted
upper-level ridge over the Pacific Northwest and the upper-level
cutoff low over Arizona through Saturday which will result in near
normal temperatures. We say good riddance to fire weather concerns
and hello to renewed chances for rainfall beginning Sunday night.
While rainfall totals with this system have trended downwards,
widespread rainfall is still expected with amounts tapering from
north to south. This is not looking like a fire season ending event
(~2.0 inches of rain within 72 hours), but even non-fire season
ending events are beneficial and this Red Flag Warning event is a
prime example of that.

&&

.AVIATION...
(06Z TAFS)
Issued at 934 PM PST Wed Nov 6 2024

High confidence VFR through the TAF period continues with mostly
clear skies over the terminals. Winds have diminished to light to
moderate but remains mostly offshore. W/NW winds will return by
Thursday afternoon but will still remain light to moderate.

Vicinity of SFO...VFR through the TAF period. NE/E winds will linger
into the night but will be light. Winds increase Thursday afternoon
but will remain moderate and will become westerly.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...High confidence VFR through the TAF period.
Light S/SE winds will continue until Thursday afternoon where winds
build to moderate and become W/NW.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 934 PM PST Wed Nov 6 2024

As the gradients become weaker, the Northerly winds will continue
to diminish tonight and turn light and variable on Thursday.
Weaker winds and a decaying northerly swell will lead to an
improved sea state. Breezy northwest winds will build again early
next week.

&&

.FIRE WEATHER...
Issued at 753 PM PST Wed Nov 6 2024

Red Flag conditions are still being observed in portions of the
Bay Area. The most critical area remains the North Bay Interior
Mountains, where higher elevations winds are still gusting above
50 mph, and the RH is in the 15-25% range. Next in line is the
East Bay Mountains, where winds are gusting up to 30 mph and the
RH is in the 20-30% range. Downslope winds are also keeping dry
air around along the Eastern San Francisco Bay Shore, where the
wind is gusting to 15 mph and the RH is around 20-25%. Similar
downslope flow is affecting the San Mateo coast, where winds are
also gusting to 15 mph with RH in the mid 20s. For these areas,
there has been no change, the Red Flag Warning continues through 7
AM Thursday. On the other hand, we have seen significant
improvement in the wind speed throughout the City of San
Francisco, East Bay Interior Valleys, Santa Clara Valley, Eastern
Santa Clara Hills, Santa Cruz Mountains and Northern Monterey Bay,
and the Red Flag Warning was cancelled in those areas. There is
still some dry air across the inland valleys, but the winds speeds
are generally below 5-10 mph. There are some stronger winds (up
to 15 mph) in the Santa Cruz Mountains, but the humidity is also
higher (45-50%) in this zone. Further improvement is expected
through the night for all zones, with the exception of the North
Bay Interior Mountains, where strong winds will persist through
the early morning hours.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 7 AM PST this morning for CAZ502>504-506-
     508-509-515.

PZ...None.
&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...SO
MARINE...SO

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