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000
FXUS66 KMTR 042345
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
445 PM PDT Wed Oct 4 2023

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 239 PM PDT Wed Oct 4 2023

Warm temperatures expected through the end of the week with
elevated HeatRisk across much of the interior. A Heat Advisory is
in effect for SF Peninsula, SF Bay Shoreline, Santa Clara Valley
(including San Jose), and the Santa Cruz Mountains starting at 11
am Thursday lasting until 11 pm Friday. Heat will begin to ease
on Saturday but will still 5 to 15 degrees above climatological
normals. Cooler temperatures really arrive Sunday into early next
week as pattern change will be underway.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 239 PM PDT Wed Oct 4 2023

Upper level ridging persists offshore with the apex of high pressure
(591 dm) west of the Pacific NW. 500 mb heights will slowly rise
across the Bay Area and Central coast today as this high pressure
feature nudges east today. Associated warmer temperatures aloft are
also expected to move in through the day today. In addition,
offshore (NE) flow aloft and subsequent downsloping winds is
contributing to additional warming for some valley regions (e.g.
North Bay valleys, Santa Clara Valley) and coastal spots (e.g.
Santa Cruz). All these factors in addition to those warmer
temperatures aloft plus a compressed/nonexistent marine layer will
result in warmer temperatures across the region today.

Today is the start of the anticipated warmup with temperatures
already climbing early this afternoon. Temperatures will max out
today in the low 90s across interior valleys and mid 90s for the
hills (Coastal NB Mtns, East Bay Hills, SC Mtns, for example). Near
the coast, temperatures will reach mid 80s. There`s more widespread
Moderate HeatRisk today across the 101 corridor from the North Bay
down to Salinas, meaning those sensitive to heat should use caution
today if planning to be outside. Not expecting any official
records to be broken today, however.

Warming trend continues into tomorrow. NBM features a high
likelihood (70-100%) of max temps over 90 degrees across much of the
interior valleys, the Santa Lucias, and the Santa Cruz Mountains.
For temperatures over 100 degrees, NBM highlights the SC Mountains
with a high likelihood for hot spots like Ben Lomond tucked in
the hwy 9 corridor and a moderate chance for southern Santa Clara
Valley (places like Gilroy). Elevated HeatRisk will persist with
Moderate HeatRisk blanketing much of the interior tomorrow, while Major
HeatRisk is anticipated across the Santa Clara Valley, portions
of the bay shoreline as well as the Santa Cruz Mountains. Major
HeatRisk means that anyone without effective cooling and/or
adequate hydration has a higher chance of being impacted by heat
illnesses if precautions are not taken.

Due to widespread elevated HeatRisk tomorrow, a Heat Advisory has
been issued for the SF Peninsula, the SF Bay Shoreline, the Santa
Cruz Mountains, and the Santa Clara Valley from 11 am tomorrow
through 11 pm Friday. Continue to practice heat safety, stay
hydrated, and don`t perform strenuous activity during peak heating
in the afternoon.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 239 PM PDT Wed Oct 4 2023

High pressure will continue to gradually build in through the end of
the week with warm and dry airmass will persisting over the area.
Airmass aloft will continue to warm and by Thursday night, 850 mb
temps approach the 90th percentile values for this time of year at
20-21 deg C (68-69 F) according to OAK sounding climatology.
Overnight lows will be warmer Thursday into Friday with lows in
the mid 60s across the Bay Shoreline and up to low 70s near across
thermal belts (generally above 1500 feet). Low 60s are forecast
for coastal regions and NB Valleys, so there will be some relief
for those spots. Moderate to Major HeatRisk continues Friday. As
such, the Heat Advisory remains in effect through 11 PM Friday.

By Saturday, warm temperatures will continue but signs of a cooldown
will be in sight as apex of ridge shifts east into the Intermountain
West. Much cooler temperatures are expected by Sunday into early
next week thanks to an incoming upper low that will move across the
Pacific NW/NorCal. There`s even a very small chance for light rain
late Monday into Tuesday. We will continue to monitor closely!

&&

.AVIATION...
(00Z TAFS)
Issued at 445 PM PDT Wed Oct 4 2023

High confidence in VFR through the TAF period across the region.
Breezy offshore flow continues for the inland terminals, with
onshore flow closer to the coast. Winds diminish overnight, with
generally light winds Thursday afternoon

Vicinity of SFO... VFR through the TAF period. Breezy northwest
winds developing for a couple hours today, before resuming on
Thursday.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR through the TAF period. Breezy onshore
flow, up to 10-12 knots, until the evening hours. Winds diminish and
become offshore overnight and Thursday morning, until onshore flow
reasserts itself in the afternoon hours.

&&

.MARINE...
(Tonight through next Monday)
Issued at 445 PM PDT Wed Oct 4 2023

Generally light to moderate north winds expected through the
weekend. Current northwest swell continues to diminish through the
weekend and a new, light northwest swell train arrives early
Friday. Light southerly swell continues into next week.

&&

.CLIMATE...

Record high data for this week:

Location       Oct 4th         Oct 5th     Oct 6th     Oct 7th
------------------------------------------------------------------
Santa Rosa     101 1920       103 1933     102 1930    99 1996
Kentfield       99 1987       100 1987      97 1930   100 1996
Napa           100 1987       101 1987      96 1930    99 1996
Richmond        99 1987        99 1987      91 1996    96 1996
Livermore      106 1980       100 1980     100 2014   101 1980
San Francisco  100 1987       102 1987      94 1992    98 1996
SFO             95 1987        99 1987      92 1992    92 1996
Redwood City   101 1980        99 1987      99 1987    95 1996
Half Moon Bay   87 1953        82 2013      87 1972    89 1992
Oakland City    92 2014        96 1987      93 1976    90 1992
Salinas        100 1987       105 1987      95 1972    94 1996
King City      106 1944       105 1933     100 1996   102 1996

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 11 AM Thursday to 11 PM PDT Friday for CAZ006-
     508-512-513.

PZ...None.
&&

$$

SHORT TERM...McCorkle
LONG TERM....McCorkle
AVIATION...DialH
MARINE...DialH

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