381
FXUS66 KMTR 141043
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
343 AM PDT Fri Jun 14 2024

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

.SYNOPSIS...
Issued at 208 AM PDT Fri Jun 14 2024

Slight temperature warm up for Friday, especially away from the
coast. Near normal temperatures over the weekend. Northerly winds
will increase later Friday and persist over the weekend. The
stronger winds will lead to hazardous conditions over the coastal
waters and elevated fire weather conditions overland. Longer range
outlook shows a notable warm up late next week.


&&

.SHORT TERM...
Issued at 208 AM PDT Fri Jun 14 2024
(Today and tonight)

Overnight satellite imagery shows a June Gloom-ish type picture
with marine layer stratus covering the coast from the Golden Gate
southward. The stratus is also at a depth of 1700 feet per Fort
Ord profiler with decent inland coverage around Monterey Bay,
Hollister, and Salinas Valley. Despite the cloudy start for some
areas, today will generally be warmer than Thursday. The reason?
Building shortwave ridge aloft in from the south and increasing
N-S gradient (SFO-ACV). In other words, a higher likelihood of
seeing sunshine today, even at the coast. Temperatures today will
be in the 60s to mid 70s coast/bays and upper 70s to upper 90s
inland. The warmest temperatures will be interior portions of
Monterey/San Benito with isolated HeatRisk values in the Moderate
category.

For tonight, the shortwave ridge building in from the south will
battle a passing upper level trough through NorCal and the PacNW.
This passing trough will help to established increasing N-S
pressure gradients and developing offshore flow over the higher
terrain. As a result, the marine layer will be much less and
confined more to the coast.

&&

.LONG TERM...
Issued at 250 AM PDT Fri Jun 14 2024
(Saturday through Thursday)

The weekend into early next week: the shortwave ridge gets
flattened as the aforementioned longwave trough (embedded upper
low) becomes more entrenched across the West Coast. The end
result? Cooler, but seasonable, temperatures. Highs ranging from
60s to mid 70s coast/bays and mid 70s to lower 90s inland. The
more noteworthy weather item over the weekend will be the
increasing northerly flow leading to marine hazards and fire
weather concerns. See MARINE and FIRE WEATHER sections for
specific details. Generally speaking, the northerly gradient will
increase further and peak close to -8.5mb for SFO-ACV by Saturday
night/Sunday. That type of set up will make it hard for the marine
layer to remain , but also support wind gusts of 35-45 mph. Could
even see some gusts approach 50 mph over the coastal waters.
Confidence is pretty high for the stronger wind potential as
ensembles and ECMWF Extreme Forecast Index highlight portions of
the CWA. In fact, the ECMWF EFI pin-points strongest winds along
the Big Sur coast south to Pt Conception. While not strong enough
to warrant a Wind Advisory they will be able to blow loose items
around, especially along the coast, bays, and N-S oriented
valleys.

Tuesday and beyond: Winds finally ease as the N-S begins to relax
mitigating Marine and Fire Weather concerns. Interesting evolution
of the longwave pattern middle of next week. While the pattern
looks "troughy" it does show rising 500 mb heights over CA. More
importantly, the warming of 850 mb temperatures. This begins to
show up by Wednesday and then continue through next week. Rising
500 mb heights and warming 850 mb temperatures will kick off a
warming and trend. Latest long range outlook from WPC highlights
portions of the Central Valley and SoCal for Excessive Heat.
Cluster analysis and NBM guidance supports this highlighting from
WPC. Official forecast late next weekend has triple heat
impacting interior portions of the Bay Area and Central Coast.
Will need to monitor over the coming days.



&&

.AVIATION...
(06Z TAFS)
Issued at 1102 PM PDT Thu Jun 13 2024

MVFR-IFR stratus is developing along the immediate coast and into
the East Bay north of OAK and across the Central Coast valleys.
Stratus coverage tonight is expected to expand slightly into the
northern SF Bay and patches of the Napa Valley. Lingering breezy
onshore winds will diminish through the rest of the night.

Stratus will clear out through Friday morning, with intensely breezy
west winds developing on Friday afternoon. Wind gusts are expected
to approach 20-30 knots at the terminals in the afternoon, with
strong gusts continuing through the evening. Model output indicates
that surface sustained winds will begin to diminish as the nocturnal
boundary layer decouples, but strong winds aloft will introduce the
risk of LLWS overnight. Model output shows signals of LLWS along the
coast, but magnitudes are not strong enough to include in the TAFs
at this time.

Vicinity of SFO... Westerly winds expected to diminish through the
night, with a moderate confidence for MVFR-IFR stratus to flow over
the terminal. OAK is just on the edge of the stratus deck, but has
consistently reported MVFR cigs which is reflected in their TAF
forecast. VFR conditions return Friday morning with strong west-
northwest winds developing Friday afternoon. Current forecast calls
for gusts around 30 knots extending late into the evening as winds
funnel through the San Bruno Gap, only coming down as the TAF period
ends. LLWS concerns develop on Friday evening but the magnitude is
marginal and confidence is low.

SFO Bridge Approach... Lower confidence for stratus impacts along
the approach path. Otherwise similar to SFO.

Monterey Bay Terminals... IFR-MVFR ceilings continue through the
night. Stratus clears out through Friday morning with low to
moderate confidence in timing at MRY. Breezy onshore winds gusting
to 15-20 knots develop Friday afternoon and last into the evening.
Model output suggests that the region remains clear through the end
of the TAF period and some portion beyond.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1102 PM PDT Thu Jun 13 2024

Fresh to strong northwest winds persist over the northern waters
with gale force gusts expected Friday afternoon and evening.
Strong north to northwest winds will spread southwards over much
of the coastal waters late Friday into Saturday, with widespread
gale force winds anticipated. Significant wave heights up to
around 12 to 15 feet in the outer waters and 10 to 14 feet in the
inner waters continue into the weekend. Hazardous conditions for
small craft continue through the weekend and early next week.

&&

.FIRE WEATHER...
Issued at 315 AM PDT Fri Jun 14 2024

...Elevated Fire Weather Conditions Through The Weekend...

*Less impactful marine layer
*Increasing northerly winds, especially higher terrain
*Lowering relative humidity values day and night

No notable change from previous forecast. Friday will feature the
last full day of onshore flow with an impactful marine layer
(cool/higher RH). By late Friday night/early Saturday winds become
more northerly over the higher terrain of the N and E Bay with
gusts 25-35 mph. The developing offshore flow will usher in
moderate to locally poor humidity recoveries above 1,000 feet. The
drier airmass will ultimately spread across the entire district
Saturday afternoon with 15-30% RH minimums across the interior. A
slight uptick in RH recoveries on Saturday night as the marine
layer tries to re-establish itself below 1,000 feet. Above 1,000
feet will feature another night with moderate to locally poor
humidity recoveries Saturday night into Sunday. Despite some
strong winds and lowering humidity onshore flow never completely
goes aways. It would definitely be on the unusual side to issue a
Red Flag Warning in June with some hint of a marine layer/onshore
flow. Therefore, will keep a headline in place and continue to
message elevated fire weather concerns. It should be noted, that
does not mean grass fires will not be in the equation over the
weekend. Fine fuels like grass will support fires as seen by
recent fire trends. However, larger fires with thicker fuels (non-
grass) will be less likely. 100 and 1000 fuels are still holding
onto some winter moisture. A great way to visually see this is
watching ERC trends. The ERC forecast through the weekend does
show a trend toward seasonal levels, but not into the widespread
critical range.

Regardless, individuals with outdoor activities planned this
weekend should be fire weather aware. Be mindful and don`t be
"that spark".

MM

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT this afternoon 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 this afternoon through late tonight for Pt Arena
     to Pt Reyes 0-10 nm.

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

     Gale Watch from this evening through Saturday afternoon for Pt
     Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 9 AM this morning to 3 PM PDT Saturday
     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.

     Gale Watch from this afternoon through Saturday afternoon for
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60
     NM.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...DialH
MARINE...DialH

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea