298
FXUS66 KMTR 090521
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1021 PM PDT Sat Jun 8 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1205 PM PDT Sat Jun 8 2024

Seasonal temperatures with breezy onshore winds will last through
Sunday before another warm up begins Monday.

&&

.UPDATE...
Issued at 758 PM PDT Sat Jun 8 2024

The short term forecast remains in good shape, and the only
alteration to the grids was to beef up winds across the East Bay
Hills as well as the SF Peninsula as early evening mixing of 20-25
knot momentum continues. Winds across the bay side of the SF
Peninsula should subside in a few hours as nocturnal cooling
transpires. Locations along the ocean side of the peninsula as
well as across the East Bay Hills will remain a bit breezier due
to more channeling effects around the various terrain features. In
fact, NBM probabilistic guidance suggests around a 60% chance for
hourly wind gusts of at least 30 mph or greater across the East
Bay Hills and winds have been adjusted upward across this area to
reflect more of the 75th percentile output (which appears to have
captured the overachieving winds this afternoon and early
evening). Individuals across the area should anticipate wind gusts
of 25 to near 40 mph---due to acceleration around some of the
terrain---across the aforementioned areas (as well as some of the
areas along the Pacific coast).

The rest of the forecast remains largely unchanged and our
attention will turn to our next warm spell Monday through
Wednesday. Tuesday appears to be the hottest day with the
potential for upper 80s to the triple digits across the interior
portions of the area. Be sure to abide by your heat safety
protocols. Another potential impact of the above normal warmth
will be the additional drying of grasses which may result in an
uptick in fire starts. Be sure to do your part and avoid
activities that could spark a grass fire (e.g., tossing lit
cigarette ends on the ground, dragging tow chains).

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 1205 PM PDT Sat Jun 8 2024

The stratus clouds have eroded everywhere except along the
immediate coast. Despite the clearing, area profilers and the
morning sounding confirm the marine layer is roughly 2,000 ft
deep. This is allowing cool air to infiltrate into the valleys
and keep the afternoon temperatures mild.

A short wave trough at 500 mb is approaching the coast this
afternoon. This wave will amplify and become a cut-off low SW of
the Channel Islands by Sunday evening. This synoptic change will
cause the mid-level winds to shift from southerly to northerly
over the next 36 hours. This change won`t be as obvious at the
surface. While the surface wind direction should veer a bit, the
weather Sunday will continue to be dominated by a deep marine
layer, morning stratus, and breezy onshore winds in the afternoon.
Broadly speaking, the temperatures Sunday will be similar to
Saturday and the seasonal averages.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 1205 PM PDT Sat Jun 8 2024

Abandoned by the jet stream, the Southern California cut-off low
will continue to drift south Monday, allowing a ridge of high
pressure to build across the Bay Area. This ridge will cause the
marine layer to compress from 2,000 ft over the weekend to around 1,000
ft by Tuesday. While the cut-off low is part of the typical
offshore wind equation, we are missing the other piece of the
puzzle; strong high pressure over the intermountain West. While
weak offshore winds are expected at 700 mb Mon-Tue, they likely
won`t reach the surface. The combination of offshore winds aloft,
and a shallow marine layer will cause inland areas to warm above
seasonal averages from Monday through Wednesday. Tuesday currently
looks like the warmest day of the week, with inland highs in the
90s. Coastal areas will stay in the 60s and 70s.

By Thursday, an approaching trough will kick the cut-off low
inland, where it will quickly weaken. This will bring the return
of onshore flow and allow temperatures cool back to the seasonal
average.

&&

.AVIATION...
(06Z TAFS)
Issued at 1017 PM PDT Sat Jun 8 2024

Currently VFR at all terminals with not a cloud in the sky. High
confidence in VFR through the TAF period at all terminals except the
Monterey Bay terminals of MRY and SNS. Winds will remain onshore
through the TAF period, becoming gusty this afternoon.

Vicinity of SFO...Currently VFR with easterly flow. Moderate
confidence in VFR through the TAF period. Winds will transition to
become westerly and gusty this afternoon with gusts up to 25 knots
to be expected. Winds will diminish overnight and remain westerly
through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with northwesterly flow at
both terminals. Winds will prevail out of the west for MRY and out
of the northwest for SNS through the TAF period. Confidence is not
high on if the terminals will see any reduction in flight category
through the TAF period; however, with the pattern being dominated by
high pressure, the most likely outcome would be LIFR conditions in
the early-to-mid morning hours with greater confidence of occurrence
at MRY as compared to SNS due to the proximity to the Pacific Ocean.

&&

.MARINE...
(Tonight through next Friday)
Issued at 1017 PM PDT Sat Jun 8 2024

The pressure gradient between subtropical high pressure over the
Eastern Pacific Ocean and low pressure over the Southwest
continues to allow for moderate to fresh northwesterly breezes to
prevail. As high pressure slowly encroaches towards the West
Coast, the pressure gradient will tighten, causing the wind speed
to increase through Sunday with gale force gusts possible over the
northern zones. A fresh to strong northwesterly breeze will
persist through next week. Significant wave heights will mostly be
dominated by wind driven waves, though there is a moderate
northwesterly swell and a low southwesterly swell mixed in.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for SF Bay N of Bay
     Bridge.

     Small Craft Advisory from 3 PM to 9 PM PDT Sunday for Mry Bay.

     Small Craft Advisory until 9 AM PDT Monday 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-Pt Reyes to Pigeon Pt 0-10 nm.

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

     Small Craft Advisory from 9 AM Sunday to 9 AM PDT Monday for Pt
     Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Sarment
MARINE...Sarment

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