Gale Warning 23, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1103 AM PDT Sun Mar 26 2023

.SYNOPSIS...Chilly overnight and early morning temperatures with
drier conditions through Monday morning. Prepare for another round
of wind and rain for early next week with the brunt of the storm's
impacts expected on Tuesday.

&&

...Wind and Rain Impacts Early Next Week...

.DISCUSSION...as of 03:49 AM PDT Sunday...Fairly quiet mid shift
with dry weather while the breezy to moderately gusty winds from
last night have diminished to lighter winds. For the most part,
current temperatures are similar to 4 degrees cooler than 24 hours
ago. Thermometers across our CWA are currently reading between the
mid 30s to the mid 40s (warmer closer to the coasts or bay
shorelines) and coolest across the interior and over higher
terrain. Daytime highs this afternoon will once again range from
the low 50s to low 60s. Given that weather will remain mild today,
please take care of any storm prep you may need to do ahead of

Model guidance continues to support that the cooler air aloft will
remain in place through Monday morning. In coordination with
neighboring offices, we have expanded the current Frost Advisory
across most of our CWA through 9 am Monday with the emphasis
being on Sunday and Monday mornings from 4 am to 9 am. In
general, temps will drop into the low 30s to mid 30s making for
very cold conditions, especially for unsheltered populations or
folks that do not have power in their homes to provide a heat
source. However, don't forget to protect pets and sensitive
vegetation as well.

Focus remains on the incoming storm early this week as an upper
low from the Gulf of Alaska tracks southward over the ocean, but
close to the CA coast. Rain will be arriving Monday evening to
the North Bay and then by late Monday night to the rest of the Bay
Area including Santa Cruz county. Precipitation will continue to
spread southward into Central CA (San Benito and Monterey
counties) overnight Monday into early Tuesday morning. The
heaviest rain is forecast for the North Bay between 11 pm Monday
thru 11 am Tuesday. For areas south of the Golden Gate Bridge,
heaviest rain is forecast between 5 am to 5 pm Tuesday. WPC QPF
guidance was nudged up slightly for the coastal mountains of Santa
Cruz and Monterey counties. However, there was a much more
noticeable increase in QPF across North Bay, especially in Marin
and Sonoma counties where storm total QPF amounts from Monday
through Wednesday increased by 0.5" to almost an inch in most
areas. New storm totals for North Bay during this time are now
1.5" to 2.5" for the valleys with 2.5" to a little over 4" for
higher terrain. With this increase in QPF, we coordinated with
WPC asking that the Slight (15-39%) risk of ERO (Excessive
Rainfall Outlook) be expanded to include the coastal North Bay
region for Tuesday. Meanwhile, the rest of our CWA is only in the
Marginal risk for an ERO (5-14%). Please prepare for urban/small
stream flooding and pay attention to forecast updates, especially
as the storm moves through for any flood products our office may
issue. Although some of that QPF will fall as snow, that
is limited mostly to the higher elevations of the Mayacamas
mountains near the Napa, Sonoma, and Lake county border with up to
4 inches of snow possible. The East Bay Hills and Santa Cruz
mountains may see up to an inch. The Santa Lucia Mountains in
Monterey County will have the highest amounts ranging 1-6"
although a few higher peaks may go up to 8 or 10 inches. As
precipitation arrives, snow levels will initially be between 2000
to 3000 ft Monday evening then rise to 4000 to 5000 ft Tuesday
morning before lowering back down to around 3000 ft by Tuesday
afternoon. Another variable to worry about with precipitation is
that we have a slight chance (less than 20%) of thunderstorms
Tuesday evening into early Wednesday morning...primarily in the
North Bay

Beyond rain, snow, and thunderstorms, the other impactful variable
will be strengthening winds as the storm makes its southward track
along the CA coast. Gusty winds will begin over the northern coastal
waters Monday evening. Winds over land will begin to get gusty
late Monday night and continue into much of Tuesday. Strongest
gusts will range 35 to 55 mph which will increase the risk of more
downed trees and potential power outages.

Although the brunt of this storm system will occur late Monday
into Tuesday, this storm will remain in the area as it slowly
tracks southward into SoCal by early Thursday morning. Thus,
lighter rain showers will continue on Wednesday into early
Thursday.

Weak ridging develops over our CWA Thursday afternoon into Friday.
However, both deterministic and ensemble models indicate that
we should expect a wet pattern to return next weekend in the first
few days of April.

&&

.AVIATION...as of 10:42 AM Sunday....For the 18Z TAFs. Widespread
VFR through the TAF period. Current satellite and camera imagery
show clear skies across the region. Winds are generally light to
moderate, though breezy onshore winds start to develop again in
the late afternoon, with gusty conditions in the KSFO and KOAK
region. Overall, winds will be less gusty than in previous days
as pressure gradients continue to weaken. Winds gradually weaken
late in the evening, then becoming light and variable in the early
morning hours of Monday.

Vicinity of SFO...VFR through the TAF period. Winds are currently
light, but expected to increase and become stronger around the
early afternoon hours, with speeds of 15-20 kt, and moderate
potential for gusts to 25 kt. Winds decrease in the late
evening, becoming light near the early morning hours of Monday.
Towards the end of the TAF period, high clouds begin to move in,
with winds turning to become more southwesterly.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR at area terminals through the end of
the TAF period. Breezy NW winds return this afternoon, with speeds
around 10-15 kt. Winds weaken moving into the late evening
becoming light and variable in the overnight hours of Sunday into
Monday.

&&

.MARINE...as of 10:41 AM PDT Sunday...Strong northerly winds this
morning are beginning to weaken. This weakening trend continues
through the afternoon but stronger, near gale force gusts persist
along the immediate coast. Northwest  swell continues to decay but
steep hazardous seas remain in the  outer waters. A low pressure
system continues to develop over the eastern Pacific which will
bring rain and wind to the coastal  waters and bays late Monday
into Tuesday, with gales likely  returning.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Frost Advisory...CAZ503-504-506-510-512>518-528-529
             SCA...Mry Bay from 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm

&&

PUBLIC FORECAST: JBB
AVIATION: AC
MARINE: Lorber

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