618
FXUS66 KMTR 031801
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1101 AM PDT Mon Jun 3 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1254 PM PDT Sun Jun 2 2024

Cooler temperatures hang on through today with breezy daytime
winds and marine layer stratus overnight. Tuesday sees a dramatic
warmup with a Heat Advisory in effect for the inland areas through
Thursday. Temperatures will moderate towards the latter part of
the week.

&&

.SHORT TERM...
(Today and tonight)
Issued at 413 AM PDT Mon Jun 3 2024

Milder morning temperatures are occuring courtesy of a mix of low
clouds and incoming higher level clouds from the northwest, higher
dewpoint temperatures (measure of water vapor), areas of mixing
surface winds and the lower level temperature inversion (all
slowing nocturnal radiative cooling). Dewpoint temperatures are
mainly in the lower to mid 50s across the forecast area, in
contact with 50F-54F sea surface temperatures helping to form
coastal fog and drizzle. Higher water vapor also extends into the
vertical, precipitable water (pw) on last evening`s Oakland upper
air sounding was 1.19" which is near the long term max moving
average in early June. The GFS has been forecasting the pw to
peak near 1.40" by late this morning, not far from a couple daily
maximums ~ 1.50"-1.55" on the period of record (since 1948) in
early to mid June.

With 500 mb heights mainly at or slightly greater than 580
decameters (about typical for June) there isn`t enough broad based
cooling e.g. positive vorticity to largely precipitate out the
increased water vapor at our latitude (like it certainly could in
winter season), rather like Sunday morning on the coastline, the
higher levels of water vapor may still produce either patchy
coastal drizzle or very light rain, add in a surface based cool
front forecast to arrive later today and this too may help further
produce light measurable precipitation, best chances on the
coastline.

A fair amount of clouds are rolling in, the best chance of sunny
breaks today will be inland and during the afternoon. Daytime
highs will be about the same today compared to Sunday except cooler
farther inland, i.e. due to increasing cloud cover and post frontal
cool air advection later today. Some coastal stratus is likely to
roll back in this evening, lower level winds also shifting to north
to northeasterly direction starting late tonight.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 413 AM PDT Mon Jun 3 2024

Model forecasts are consistently showing a steepening ACV-SFO
pressure gradient, increasing 925 mb and 850 mb temperatures and
steadily climbing 500 mb heights Tuesday, all indicating higher
pressure moving in and warmer to hotter temperatures soon to
develop over the forecast area. Lower to mid level tropospheric
temperatures will increase under compressional warming, readings
nearing the max moving average for early June, 500 mb heights
(peaking near 590 decameters) will be between the 90th percentile
and the max moving average in early June. As we have been
advertising, it`ll turn warm to hot fairly quickly especially
inland. A heat advisory remains in effect Tuesday-Thursday. The
marine layer will become compressed, likely to 1000 feet or less,
preventing inland areas from receiving afternoon & evening sea
breeze relief. Midweek timeframe by midday Wednesday is when the
apex of 500 mb heights will pass east of our forecast area, the
center of the high continuing to shift eastward reaching NM/TX
late week before becoming approximately stationary; a strong zonal
jet stream across the Pacific and western CONUS likely helping to
at least initially move the ridge well inland at a quickened pace.

Have mentioned in a previous discussion current coastal sea surface
temperatures are in good shape, running 1F to 2F below June normals
and the PDO is in negative phase. This will help restore a sea
breeze, question is how quickly later on this week, plus pw values
are forecast to remain above normal even during mid to late week
which will eventually help restore coastal stratus & fog. To add,
more recent meso-scale and global model output have scaled back
the potential for a coastally trapped southerly wind reversal here
in our forecast area mid to late week. It still may happen, can`t
completely rule it out, but from a numerical weather prediction
aspect it currently looks less favorable. Rather a reinforcement
of surface high pressure over the coastal and offshore waters may
bring in cooler air, re-establishing an onshore SFO-SAC pressure
gradient while the ACV-SFO pressure gradient (northerly winds)
will have already decreased by late week.

Helpful life saving information/tips from previous discussion:

Moderate HeatRisk is expected for the inland North Bay, the East and
South Bays, and the inland Central Coast through Thursday, meaning
that there`s a moderate risk of heat-related illnesses for sensitive
populations (children, the elderly, pregnant women, those with
certain medical conditions, or anyone working outside without
cooling or hydration). In addition, we`re also starting to see major
HeatRisk in some areas of the North Bay valleys and far eastern
Contra Costa county on Tuesday, corresponding to a major risk of
heat-related illnesses to anyone without effective cooling, adequate
hydration, or both. Here are some heat safety tips:

* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.

&&

.AVIATION...
(18Z TAFS)
Issued at 1101 AM PDT Mon Jun 3 2024

High clouds are widespread across the region this morning with
MVFR/IFR CIGs around the Monterey Bay region and San Francisco Bay
terminals. These conditions are expected to improve late
morning/early afternoon across the Bay Area, yet may stick around
for places such as KMRY. Onshore winds are forecast to increase this
afternoon and continue to be breezy at times throughout the evening
with gusts in the 20-25 knot range, locally stronger for KSFO. Into
the evening, as high pressure sets in, and upper level winds turn to
become northerly inducing directional LLWS at select terminals,
expecting stratus to slowly erode as the lower levels dry out and
are sapped of moisture. This should lead to widespread VFR for most
terminals north of Monterey Bay. Meanwhile, KMRY and KSNS are most
likely to see lowering visibilities/ceilings early Tuesday morning.

Vicinity of SFO...Currently IFR. Through late morning and early
afternoon, ceilings will slowly rise to become MVFR towards noon.
Late clearing of stratus is expected in the afternoon, becoming VFR
but with SCT low clouds as winds increase and gust to around 30
knots out of the west. Clouds are anticipated to continue to
dissipate through the end of the TAF period leading to widespread
VFR. Winds gradually diminish through late evening and into the
overnight hours. Winds will begin to increase by mid-to-late Tuesday
morning.

SFO Bridge Approach...Winds will be weaker over the approach.
Otherwise, similar to SFO.

Monterey Bay Terminals...LIFR conditions persist through the late
morning, but CIGs are expected to lift now that the sun has risen as
diurnal heating begins, eventually achieving MVFR in the late
afternoon. Not expecting VFR to last long at KMRY, in fact, low
confidence in clearing whatsoever. Therefore, have included a TEMPO
for brief and intermittent VFR conditions in the afternoon. Winds
breezy and westerly in the afternoon today should help maintain the
stratus feed. IFR/LIFR ceilings and/or visibilities return in the
nighttime and continue into Tuesday morning.

&&

.MARINE...
(Today through Saturday)
Issued at 1101 AM PDT Mon Jun 3 2024

Moderate to fresh northwest winds persist through midweek, but
increase to become strong towards Tuesday night into Wednesday
with gale force gusts possible in the northern waters. Moderate
wave heights will persist before rough seas build towards midweek
with significant wave heights of 10-12 feet expected.

&&

.CLIMATE...
Issued at 127 AM PDT Sat Jun 1 2024

Record high temperatures at the long term climate stations for
June 4th and 5th:

Station             June 4th             June 5th

Santa Rosa          98 in 1949           102 in 1926
Kentfield          101 in 1981           102 in 1926
Napa               102 in 1981           105 in 1903
Richmond            90 in 1955            86 in 1983
Livermore          105 in 1960           104 in 1926
San Francisco       92 in 1949            95 in 1883
SFO Airport         92 in 1955, 1949      89 in 1972
Redwood City       100 in 1981            97 in 2002, 1972
Half Moon Bay       71 in 1955            74 in 1958
Oakland downtown    96 in 1981            87 in 2002
San Jose            98 in 1904           100 in 1926
Salinas Airport     92 in 1949            87 in 1949
King City          102 in 1981, 1957     105 in 1926

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 8 AM Tuesday to midnight PDT Thursday night
     for CAZ503-504-506-510-515.

     Heat Advisory from 8 AM Wednesday to midnight PDT Thursday night
     for CAZ513-514-518.

PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay.

     Small Craft Advisory from 3 PM this afternoon to 3 PM PDT
     Tuesday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
     Tuesday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory from 9 AM to 3 PM PDT Tuesday for Pigeon Pt
     to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 PM PDT Tuesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Canepa
LONG TERM....Canepa
AVIATION...RGass
MARINE...RGass

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