523
FXUS66 KMTR 182039
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
139 PM PDT Thu Jul 18 2024

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 1252 PM PDT Thu Jul 18 2024

Warmer temperatures begin today and will last through next week.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 1252 PM PDT Thu Jul 18 2024

A short wave trough off the coast of British Colombia will move
inland and weaken over the next 36 hours. At the same time, a 500
mb ridge will develop across the bay area, anchored by strong high
pressure centered over Arizona. This building ridge will cause
surface temperatures to increase through Friday, with triple digit
heat expected at several inland locations. Onshore winds will
remain at the surface, and the shallow marine layer will continue
to keep coastal areas in the 70s.

I continued to us a blend of NBM that comes out to the 62.5
percentile for daily maxT. I`m lured above the deterministic and
ensemble mean by the very warm ECMWF ensemble and deterministic
runs, which are now being supported by high resolution models and
confirmed by some temps already in the 90s today.

A Heat Advisory is in effect for interior portions of the North
Bay, East Bay, South Bay, and interior portions of Monterey and
San Benito Counties through 11 PM Friday night.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 1252 PM PDT Thu Jul 18 2024

Another weak mid-level disturbance will slide along the western
periphery of the SW US high, disrupting the ridge and allowing
surface temps to drop a bit over the weekend. While still above
normal, there wont be many triple digit thermometers over the
weekend and the Heat Advisory is not currently in effect on
Saturday or Sunday. At the surface, the gradient between
subtropical high pressure and the California trough will tighten,
and onshore winds will be stronger than they have been. Winds
will be strongest at higher elevations in the East Bay. If you`re
climbing Mt. Diablo on Saturday afternoon, winds may gust to gale
force near the summit.

By Monday, the pattern gets more complicated. The weekend
disturbance will be out of the picture, allowing the ridge to
rebuild over central California. At the same time, a new upper
level trough will approach the PNW from stage left. This will
bring the temperature back to normal in Seattle for the first time
in 3 weeks, but doesn`t look to have much effect in the Bay Area,
as the stubborn high pressure remains entrenched. While there is
still a fair bit of uncertainty, it`s safe to assume next week
will be well above normal for inland areas. Looking way ahead,
there may be a cold front that finally rids us of this high
pressure and brings much cooler weather in time for next weekend.
We`ll be glad to see it go, as it`s been influencing our weather
since the 4th of July.

&&

.AVIATION...
(18Z TAFS)
Issued at 1058 AM PDT Thu Jul 18 2024

Satellite shows fog starting to dissipate close to MRY. Given
satellite trends, fog could dissipate as soon as 18Z but is expected
to fully dissipate by 1830Z. A more compressed marine layer will
keep stratus confined closer to the coastline tonight with low
confidence that stratus will extend inland. In the case that stratus
does move inland, SFO and OAK will be the two inland airports most
likely to see IFR CIGs develop. Along the Central Coast, IFR to LIFR
CIGs are anticipated at MRY and SNS overnight with some potential
for fog to develop during the early morning. Onshore flow from the
west to northwest continues through the TAF period. Winds will
strengthen during the afternoon with locally gustier conditions
expected over SFO into the evening.

Vicinity of SFO...VFR through the TAF period with low confidence
that IFR CIGs will develop overnight. The marine layer has continued
to compress which decreases confidence that stratus will extend into
SFO tonight. If stratus does reach SFO it will most likely be after
08Z with IFR CIGs most likely. Onshore flow continues through the
period with gusts up to 30 knots possible this afternoon through the
evening. A small number of models indicated gusts up to 31-32 knots
may be possible but confidence remains low.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Satellite shows fog clearing around MRY
with full clearing expected by 1830Z. VFR conditions briefly return
by late morning and continue into the evening before stratus and
LIFR CIGs return overnight. Confidence on stratus return is low to
moderate with guidance split on stratus would moving inland or
staying confined along the edge of the Monterey Bay. Onshore flow
continues through the TAF period with moderate winds expected during
the afternoon.

&&

.MARINE...
(Today through Tuesday)
Issued at 1058 AM PDT Thu Jul 18 2024

High pressure over the Eastern Pacific Ocean will be the
dominating feature through the forecast period. As the pressure
gradient tightens, northwesterly breezes will become strong with
near gale force gusts. Gale force gusts are to be expected over
the northern waters. Significant wave heights in the outer waters
will build to 10 to 15 ft by Sunday and persist through the end of
the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 11 PM PDT Friday for CAZ503-504-506-510-
     513>515-517-518.

PZ...Small Craft Advisory until 3 PM PDT Friday 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.

     Gale Watch from Friday afternoon through late Friday night 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 until 9 PM PDT this evening for Pt Reyes to
     Pigeon Pt 0-10 nm.

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

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt
     to Pt Pinos 0-10 nm.

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

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Flynn

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