581
FXUS66 KMTR 151756
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1056 AM PDT Sat Jun 15 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 254 AM PDT Sat Jun 15 2024

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

&&

.UPDATE...
Issued at 917 AM PDT Sat Jun 15 2024

Drier air continues to move into our area, bringing some clear
skies this morning. Observations show moments of increased winds
in the hills and mountains up to 40-60 mph out of the north. With
the drier area and northerly winds, be sure to take precaution for
any outdoor activities that may cause any "sparks". No changes to
the forecast were made, as conditions remain on track.

SO

&&

.SHORT TERM...
Issued at 254 AM PDT Sat Jun 15 2024
(Today and tonight)

What a difference 24 hours makes...June-Gloom is all but gone. The
longwave pattern over the West remains relatively unchanged with
an upper low anchored off the BC Coast and an upper level trough
covering the PacNW into NorCal. Additionally, a weak upper level
boundary pushed through the region on Friday. The passing boundary
helped to set the stage for the much talked about burst of
northerly winds. The SFO-ACV gradient ramped up to over -6mb and
the SFO-SAC gradient topped out at over 4mb. This pressure
gradient set up is perfect for gusty northerly winds and stronger
onshore flow. A sampling of winds over the last 12 hours shows
gusts 40-60 mph, with the strongest winds over the coastal
waters, immediate coastline, higher peaks, and any inland
gap/pass. The stronger N-S gradient helped to mix out the marine
layer (June- Gloom)for the most part. Latest satellite fog product
does show some patchy stratus trying to develop along the SF
Peninsula coast, Pt Reyes, and East Bay Hills. That will be it,
patchy at best through sunrise. Lastly, the better mixed low
levels has also led to slightly warmer overnight temperatures.

Rest of today and tonight - breezy to gusty winds will persist
thanks to the stronger N-S and W-E gradients. Still not strong
enough or widespread enough for a Wind Advisory, but strong enough
for minor impacts like blowing small unsecured items around. The
biggest impact will be to the marine environment with steeper
wind waves and hazardous conditions. Interestingly enough, a very
pronounced coastal jet forms south of Pt Sur. In fact, latest
forecast has winds approaching Storm Force conditions with a few
gusts flirting with the 48 kt (55mph) mark. Moderate to high
confidence on these stronger coastal waters winds as ensemble
guidance indicate high exceedance values (80+ percent) greater
than 50 mph. Additionally, the ECMWF EFI shows how unusually
strong the winds are for this time of year and a good portion of
the ensemble members are favoring the "extreme" side. One other
impact for the persistent northerly winds over the waters will be
effective Ekman transport and increased upwelling. In other word,
colder water along the coast. The change in airmass associated
with stronger northerly flow will lead to cool temperatures
today, especially over the interior.

&&

.LONG TERM...
Issued at 335 AM PDT Sat Jun 15 2024
(Sunday through Friday)

No big changes with the overall sensible weather for Sunday and
Monday. Not much in the way of night/morning clouds and associated
marine layer thanks to persistent breezy/gusty northerly flow.
Temperatures at night will be milder thanks to better mixing and
seasonably cool during the day.

By Tuesday northerly flow will begin to slowly ease as the upper
trough weakens. In fact, the longwave pattern aloft begin to
become more zonal and then favors a more ridge like pattern for
the second half of the week into the following weekend. So what
does this pattern shift mean? A gradual warming trend with a
potential for much warmer weather by next weekend. While tonight`s
guidance may have backed off from the more "extreme heat" around
June 21/22 it is still plenty warm across the interior. Both CPC
and WPC continue to highlight portions of the Bay Area and Central
Coast for excessive heat from June 21-26.  Stay tuned...

&&

.AVIATION...
(18Z TAFS)
Issued at 1051 AM PDT Sat Jun 15 2024

Currently VFR at all terminals. High confidence in VFR through the
TAF period at all terminals as strong winds are allowing for the
marine layer to stay thoroughly mixed out. Strong winds will
impact all terminals through the TAF period, particularly
terminals within close proximity to the coast or within a
northwest-southeast oriented valley. While below LLWS criteria,
it will likely be bumpy getting out of the area.

Vicinity of SFO...Currently VFR with westerly flow. VFR through the
TAF period. AWW in effect from 21Z this afternoon through 06Z
tonight for strong westerly winds in excess of 35 knots. Westerly
winds will somewhat diminish overnight before approaching the AWW
criteria of 35 knots again tomorrow afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with northwesterly flow at
both terminals. VFR through the TAF period. Low probability and low
confidence of ceilings developing through the TAF period as the
strong winds are keeping the marine layer thoroughly mixed out, but
if ceilings were to develop they would likely be IFR-MVFR in the
early morning hours, around 12Z or so. Winds will prevail out of
the west through the TAF period, becoming gusty this afternoon.

&&

.MARINE...
(Today through Thursday)
Issued at 1051 AM PDT Sat Jun 15 2024

A tight pressure gradient over the waters will allow for strong
northwesterly breezes and widespread gale force gusts to persist
through the weekend. Significant wave heights will be 12-17 feet
through the weekend before beginning an abating trend Monday.
Hazardous conditions will linger into early next week as winds
remain strong and seas remain elevated.

&&

.FIRE WEATHER...
Issued at 345 AM PDT Sat Jun 14 2024

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

*Increasing northerly winds, especially higher terrain
*Lowering relative humidity values day and night

Forecast remains on track as northerly flow ramps up across the
district. Gusts of 30-50 mph will be more common along the coast,
higher terrain, and inland gaps/passes. Have already seen a few
isolated inland passes reach close to 60 mph as well. These
stronger winds will persist through early Monday. It should be
noted that they will not be strong the entire time, more like
bursts of stronger winds. The northerly flow has also ushered in
much drier air across the region too. 24 hour trends show some
locations 40-70% drier than 24 hours ago. While there are a few
isolated stations that may "technically" reach Red Flag criteria
conditions are not widespread enough to warrant a fire weather
zone wide Red Flag warning. Therefore, still best to message
elevated fire weather conditions through the weekend.

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 9 PM PDT this evening for SF Bay N of
     Bay Bridge.

     Small Craft Advisory from 3 PM Sunday to 3 AM PDT Monday for SF
     Bay N of Bay Bridge.

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

     Gale Warning until 3 AM PDT Monday 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...MM
LONG TERM....MM
AVIATION...Sarment
MARINE...Sarment

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