684
FXUS66 KMTR 142325
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
425 PM PDT Fri Jun 14 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 107 PM PDT Fri Jun 14 2024

Dry and windy with elevated fire concerns into early next week.
Seasonal temps and quiet weather thereafter. Potential warming
trend for late next week.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 107 PM PDT Fri Jun 14 2024

Clear across the area this afternoon as N-S gradients strengthen
further with the passing of a shortwave trough this evening. Today
will likely be the warmest day until late next week by a few
degrees for inland locations. Expecting winds to increase
initially overnight tonight in coastal gaps and high elevation
areas. Currently seeing this as winds at major sites showing
mostly a northerly component and increasing in magnitude as of the
last few hours. The ridge ultimately gets flattened by a deeper
upper level trough that will move into the West Coast. This will
keep temps down over the next several days as well as further
strengthen the N-S gradients that will promote windy conditions
into early next week.

&&

.LONG TERM...
(Sunday through next Thursday)
Issued at 107 PM PDT Fri Jun 14 2024

The most noteworthy period of wind and elevated fire weather
conditions looks like Sunday into early Monday morning when the
N-S gradient is expected to increase to around -8.5mb (SFO-ACV).
For context, this gradient peaked at -5.8 this afternoon, and -4.8
Thursday afternoon. This type of setup will support wind gusts of
35-45 mph, with some areas near the coast and higher terrain
seeing gusts up to 50 mph. Confidence remains high in this
scenario. Have decided to forgo any fire weather highlights given
the critical wind and RH values aren`t quite there. Refer to the
Fire Weather section for more.

FROM PREVIOUS DISCUSSION...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...
(00Z TAFS)
Issued at 425 PM PDT Fri Jun 14 2024

VFR conditions throughout the region, generally through the TAF
period. Model output has some probability of stratus development
tonight at the immediate coast, through the Golden Gate, and near
MRY, but confidence is low and strong winds aloft may keep the skies
clear through the nighttime. Strong northwest winds continue through
the evening hours, with gusts up to 20-30 knots at the terminals.
LLWS concerns develop along the coast this evening as strong winds
aloft decouple from the surface layer, though as of now, only STS
has strong enough shear to note in the TAFs. Strong northwest winds
expected to resume Saturday afternoon.

Vicinity of SFO... VFR through the TAF period. Strong west-northwest
winds are strengthening through the afternoon and will continue into
the evening. Current forecast has winds approaching, but not quite
reaching, 35 knots. Considered putting 35 knot gusts in the TAF, but
confidence was too low. Will continue to monitor the evolution of
winds through the afternoon and amend if necessary. Best chances for
wind gusts exceeding 35 knots are between 02-05Z. Winds will taper
off to around 10-15 knots overnight, with marginal LLWS concerns.
Strong gusts resume Saturday afternoon.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR through the rest of the day. Model
output shows some probability of IFR ceilings at MRY overnight,
but confidence is low (around a 30-40% probability) with winds
aloft remaining strong. Breezy northwest winds will diminish
overnight before resuming Saturday afternoon.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 425 PM PDT Fri Jun 14 2024

Strong north and northwest winds with gale force gusts last
through much of the weekend. 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
continue into the next work week as winds remain strong and seas
remain elevated. Seas start to diminish in the middle part of the
week.

&&

.FIRE WEATHER...
Issued at 107 PM 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 major changes from previous.

By tonight into 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/DB

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT Saturday for SF Bay N of Bay
     Bridge.

     Small Craft Advisory until 3 AM PDT Sunday for Mry Bay.

     Gale Warning until 3 AM PDT Sunday for Pigeon Pt to Pt Pinos 0-
     10 nm-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 Pinos to Pt Piedras
     Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

&&

$$

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...DialH
MARINE...DialH

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