054
FXUS66 KMTR 122103
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
203 PM PDT Fri Jul 12 2024

...New SYNOPSIS, SHORT TERM, LONG TERM, FIRE WEATHER...

.SYNOPSIS...
Issued at 154 PM PDT Fri Jul 12 2024

One more day of excessive heat for inland areas before a cool-down
over the weekend and near normal temperatures return next week.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 154 PM PDT Fri Jul 12 2024

Several of the warmer inland areas are well on their way to triple
digit heat this afternoon. Coastal areas are remaining in the upper
60s thanks to a 1,000 ft deep marine layer. As the ridge finally
moves east on Saturday, significant relief is in store, and most
guidance is trending a few degrees cooler over the last several
model runs. For example the 10/12Z, 11/12Z, and 12/12Z ECMWF runs
have predicted high temperatures at San Jose of 93, 91, and 89,
respectively. Overall the Inland temperatures on Saturday will be
roughly 10 degrees cooler than the last couple days, which will
essentially end this 11-12 day heat wave.

While the ridge weakening is good news for heat impacts, the new
pattern may support some elevated convection and there is a slight
chance for dry lightning this weekend. More details are in the
fire weather section.

&&

.LONG TERM...
(Saturday night through next Thursday)
Issued at 154 PM PDT Fri Jul 12 2024

A mid level low supported by an upper-level trough will longer off
the coast through Monday before gradually pushing onshore Tuesday.
This system will help regulate temperatures as cooler, more humid
air moves in. The lower pressure will also allow the marine layer to
gradually expand in depth and extend farther inland. We will enjoy a
return to seasonal temperatures for the majority of the week.

By next weekend, things get more uncertain. While most guidance
agrees the 4-corners high will be a semi-permanent feature, ensemble
clusters show a wide spread in the existence, timing and depth of an
approaching trough around days 7-9. Until the guidance starts to
merge on a common solution, don`t trust anything you hear about the
weather next weekend. There may be another warm-up, but 7+ day
forecasts aren`t the most reliable thing, and the uncertainty is
even higher than normal.

&&

.AVIATION...
(18Z TAFS)
Issued at 1102 AM PDT Fri Jul 12 2024

VFR prevails through the afternoon today with breezy W/NW winds.
Marine stratus will make a return in the evening tonight to bring
IFR/LIFR CIGs to North Bay and Monterey Bay terminals. There does
remain some lack of confidence as to whether stratus will form a CIG
over North Bay terminals, or predominantly remain FEW-SCT low
clouds. At this moment, confidence for CIG formation over North Bay
terminals is low-moderate. High confidence in LIFR CIGs developing
at Monterey Bay terminals tonight.

Vicinity of SFO...VFR through the TAF period. Winds NW and moderate
this afternoon, but ease slightly into the late night. Stratus will
likely impact KOAK but is not expected to bring CIGs to KSFO. Winds
at KSFO turn more W/SW into the daytime Saturday as a low approaches
the region.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the late afternoon today,
though stratus will begin to make an onshore push shortly after the
00Z hour. CIGs are expected to develop by 03/04Z with LIFR
conditions lasting through the night. Towards the early morning of
Saturday, visibilities at Monterey are likely to reduce
significantly as mist and fog develops.

&&

.MARINE...
(Today through Wednesday)
Issued at 1102 AM PDT Fri Jul 12 2024

Fresh northerly winds continue over the waters today, but decrease
to become moderate Saturday. Gentle to moderate winds then persist
through much of next week, but turn to become more southerly on
Sunday as low pressure approaches the region.  Significant wave
heights between 10 to 12 ft continue over the  outer coastal
waters with peak wave heights between 12 to 14 ft  expected over
the far northern outer coastal waters.

&&

.FIRE WEATHER...
Issued at 154 PM PDT Fri Jul 12 2024

Taking advantage of a weaker ridge, a mid-level low off the coast
will pump moisture up from the south this weekend. This elevated
moisture will lead to precipitable water values exceeding 1",
which is the 90th percentile for this time of year. Combined with
steep lapse rates, we expect this moisture to produce some
elevated convection, however, there is only a 5-10% chance of
thunderstorm development. Despite the low probability, there could
be high impacts as any lightning that does develop won`t have
much rain reach the surface, and we are come off a prolonged heat
wave which dried fuels to record levels.|

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT this evening for CAZ502-503-506-508-
     512-516-528.

     Excessive Heat Warning until 8 PM PDT this evening for CAZ504-
     510-513>515-517-518.

PZ...Small Craft Advisory until 9 AM PDT Saturday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...AC
MARINE...AC

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