High Wind in California, August 30 to 31, 2023

Area Forecast Discussion
National Weather Service San Francisco CA
431 AM PDT Wed Aug 30 2023

...New AVIATION...

.SYNOPSIS...
Issued at 259 AM PDT Wed Aug 30 2023

A Red Flag Warning is in effect for the North Bay Interior
Mountains through 8 pm Wednesday, with the area of most concern
being eastern Napa County. Strong northerly winds are building and
dry conditions in the area will lead to elevated fire weather
concerns. Elsewhere, warmer temperatures and hazy conditions
expected. Cooler temperatures return for the latter half of the
week into the weekend.

&&

.SHORT TERM...
(Today and tonight)
Issued at 259 AM PDT Wed Aug 30 2023

The overnight shift is observing the increased northerly flow as
forecasted. Winds in the higher elevations of the North Bay are
continuing to increase and should hit their overnight peak in the
next few hours. This coupled with the warm and dry overnight
conditions are verifying the fire weather concerns.

The recent forecast update added fine adjustments to the higher
elevation winds (particularly above 2000 ft) and the marine winds.
Additional tweaks were made for the temperature trend and humidity
values. But the main message remains on track for today: Dry and
warm for the interior with dangerously dry and hot conditions for
the higher peaks.

Expect triple-digit heat in the higher peaks in the interior
locations with widespread 80s and 90s for inland areas, and 60s-70s
for the coastal areas. Breezy to gusty northerly winds will be
possible through the morning and into the afternoon. Our northerly
flow will also allow for haze and smoke to filter into the area from
the fires to the north.

The offshore flow reduces into the evening, offering relief from the
dry and windy conditions, and easing fire weather concerns. This
pattern change will also help remove the wildfire smoke and haze,
leading into a much more pleasant second half of the work week.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 259 AM PDT Wed Aug 30 2023

The overnight forecasting team didn't get too much into the weeds
for the second half of the work week's forecast. Onshore flow and
cooler conditions are expected for the end of the week and into
the weekend. This will bring the temperature trend back to around
average.

Mid and longer range model and ensembles continue to entertain
chances for widespread drizzle in the North Bay early Saturday.
This looks to be the next thing the forecasting team will begin
focusing on after today's concerns, but let's stay Fire Weather
Aware today!

&&

.AVIATION...
(12Z TAFS)
Issued at 430 AM PDT Wed Aug 30 2023

VFR throughout the region. Have removed TEMPOs for IFR stratus for
the Monterey Bay terminals, as confidence has decreased through the
night. A moderate confidence for LLWS at the North Bay terminals
continues for the rest the morning. Northwesterly onshore flow
develops in the afternoon with speeds up to 10-15 knots at the
terminals. Outside of the Monterey Bay region, where IFR-LIFR
stratus is expected to develop, no stratus development expected this
evening into Thursday morning.

Vicinity of SFO... VFR through the TAF period. Light winds through
the night, with a potential shift to a northeast flow in the early
morning, before northwest winds build in the afternoon with wind
gusts up to 20-25 knots. Wind diminish late on Wednesday evening.
Beyond the TAF period, monitoring the chance for wind gusts at or
above 35 knots on Thursday afternoon and evening.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... With low relative humidities at the
surface, and no stratus patches observed on satellite, have removed
the TEMPOs for IFR ceilings this morning. Afternoon winds from the
northwest at up to 10-15 knots. A moderate confidence for IFR-LIFR
stratus developing after midnight, persisting through Thursday
morning.

&&

.MARINE...
(Today through Monday)
Issued at 259 AM PDT Wed Aug 30 2023

Strong northerly winds persist over the coastal waters thanks to
high pressure over the Eastern Pacific and low pressure inland
with gale force gusts continuing over the outermost waters. A
hazardous sea state also persists with fresh, steep wind waves.
Gusty onshore winds develop over the bays each afternoon and
evening, mainly south of the Bay Bridge and over the Monterey Bay.
Northwesterly winds over the coastal waters and afternoon winds
over the bays easing by late week with the arrival of an
unseasonably strong upper level low from the Gulf of Alaska.

&&

.FIRE WEATHER...
Issued at 259 AM PDT Wed Aug 30 2023

A Red Flag Warning is in effect for the North Bay Interior
Mountains through to 8 pm. Elevated fire weather are affecting
portions of the North Bay, mainly for eastern Napa County, as northerly
winds increase and overnight humidity recoveries were poor.
Expect strong northerly winds to last into the early morning,
then taper off by the afternoon. Predicted ERCs for the North Bay
stay near or below seasonal averages.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 8 PM PDT this evening for CAZ504.

PZ...Small Craft Advisory until 9 PM PDT Thursday for PZZ540.

     Small Craft Advisory until 3 AM PDT Thursday for PZZ545-560.

     Small Craft Advisory until 9 PM PDT this evening for PZZ565.

     Gale Warning until 9 AM PDT Thursday for PZZ570.

     Small Craft Advisory until 3 AM PDT Friday for PZZ575.

&&

SHORT TERM...Murdock
LONG TERM....Murdock
AVIATION...DialH
MARINE...DialH

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