-- Discussion containing changed information from previous version are highlighted. --
892
FXUS66 KMTR 020702
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1202 AM PDT Sun Jun 2 2024

...New AVIATION...

.SYNOPSIS...
Issued at 109 PM PDT Sat Jun 1 2024

Cooler temperatures continue into Monday with coastal stratus
developing overnight. Significant warming begins Tuesday with
moderate HeatRisk across the interior regions through Thursday.

&&

.UPDATE...
Issued at 609 PM PDT Sat Jun 1 2024

The story of the day was strong onshore wind. Several locations
around the Bay Area had gusts into the 40+ mph range, including
San Francisco and SFO. This was caused by the gradient between
strong high pressure over the Eastern Pacific, and low pressure
over the intermountain west. Zooming in, the gradient between SFO
and SAC reached as high as 4.4 mb this afternoon. The synoptic
gradient was also enhanced by much higher temperatures over the
Sacramento Valley than coastal areas stuck in the marine layer.
San Francisco only reached 62 degrees today, while Sacramento
reached 88. This warmer, less dense air contributed to the lower
pressure over the Central Valley and helped drive the onshore
winds. After decreasing late tonight and Sunday morning, winds
will pick back up in the afternoon as the pattern remains
relatively unchanged.

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 109 PM PDT Sat Jun 1 2024

Coastal stratus continues to gradually erode in the western San
Mateo Peninsula and the Monterey Bay region, expected to clear
through the rest of the afternoon. Widespread marine layer stratus
is expected again across the lower elevations in the SF Bay Area and
Central Coast tonight into Sunday morning, facilitated by a deep
marine layer (2000 ft or greater as measured by the Fort Ord
profiler). This is also helping to generally moderate temperatures
from yesterday`s warm readings. The most dramatic cooldowns have
been in the interior valleys of the East Bay, South Bay, and
southern Monterey County, where temperatures are as much as 20
degrees cooler than yesterday at the same time. The North Bay has
cooled down slightly, but downsloping winds from the coastal ranges
are themselves moderating the cooling effect of the marine layer,
which is also slightly compressed compared to the situation further
south (1200 feet as measured from the Bodega Bay profiler).

All this corresponds to high temperatures extending from the upper
70s to the lower 80s for the interior valleys, with the mid to upper
80s expected in the North Bay and southern Monterey County valleys,
mid 60s to lower 70s along the Bayshore and near Santa Cruz, and the
upper 50s to lower 60s along the Pacific coast. Lows tonight are
generally in the low to mid 50s, except down into the low 40s across
the higher elevations.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 109 PM PDT Sat Jun 1 2024

Relatively cool conditions continue into Monday. Impacts from a deep
upper-level trough impacting British Columbia will be limited, and
limited mainly to the North Bay, where the fringes of a cold front
will moderate high temperatures to the mid 70s to lower 80s in the
valleys. Any rain will be limited to the extreme northern reaches of
Sonoma County with insignificant accumulations.

The pattern changes on Tuesday with a strengthening ridge over the
Pacific migrating into the Western United States. In the interior
regions, temperatures are expected to rise into the 90s to the low
100s into Thursday with a moderate HeatRisk, meaning that there`s a
risk of heat-related illnesses for sensitive populations (children,
the elderly, pregnant women, and people without access to shade or
air conditioning). The coastal regions remain quite uncertain. The
main questions concerning the coastal forecast will any remaining
sea breezes be strong enough to outweigh the general warming trend,
how far will they travel inland, and how deep will be the remaining
marine layer be. To give just one example of the potential
uncertainty, the current forecast calls for highs in downtown San
Francisco to top out at 78, but some of the model guidance extends
into the mid 80s.

There is still a chance that the upper level trough stalls over the
West Coast, but the model ensemble clusters suggest that the most
likely outcome is that the ridge will start to build more towards
the north and bring heat impacts into the northwestern United
States. In addition, some of the global models show a southerly wind
reversal setting up sometime later on Wednesday into Thursday. With
the end of the heat still at least several days out, it`s a good
idea to stay tuned for further updates as forecast confidence
increases.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 1201 AM PDT Sun Jun 2 2024

At this hour, winds are still gusty in the SF bay region, with SFO
reporting gusts upwards of 35 knots. SFO-SAC gradient continues to
show a 4.1 mb difference, indicating these strong winds will likely
last a bit longer into the night. Nonetheless, winds are expected to
ease ever so slightly, but, will likely remain at least breezy for
most locations. Many terminals are currently seeing IFR CIGs, which
models do not seem to agree with, with many suggesting MVFR
conditions instead. Current troughing would suggest CIGs being
higher, in MVFR territory, though this is not the case. It is
possible that sea salt lofted into the lower atmosphere by strong
winds could be contributing to the formation of these low clouds by
posing as a nuclei source, and thus permitting subsequent IFR
conditions.

All to say, a bit of an uncertain forecast tonight for
the TAFs, especially in regards to CIGs. Current confidence is that
CIGs will lift in the mid morning to become MVFR. Late clearing of
stratus is expected Sunday morning to early afternoon, with strong
and gusty onshore winds redeveloping.

Vicinity of SFO...Currently IFR. Moderate confidence in clouds
beginning to lift towards the mid morning hours of Sunday to become
MVFR. Winds will continue to gust overnight but as the SFO-SAC
gradient is forecast to decrease overnight to around 1.7mb, gusts
should begin to decrease below the 30 knot mark through the night.
However, into the late morning Sunday when VFR returns, the gradient
increases once more, inducing strong and gusty westerly winds once
more approaching the 33 knot mark. It is not out of the question
that gusts may go higher than this, though confidence on gusts
reaching higher is low.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR conditions persist through the first
portion of the night, though slowly rise to become VFR by the mid to
late morning. Late clearing of stratus is expected, with VFR lasting
only a few hours in the afternoon of Sunday, and with SCT clouds.
Winds will increase out of the west to become breezy with gusts
nearing 20 knots. Stratus and low clouds return in the early evening
to bring MVFR conditions once more.
-- End Changed Discussion --

&&

.MARINE...
(Tonight through next Friday)
Issued at 609 PM PDT Sat Jun 1 2024

Strong northwest winds with gale force gusts expected over
portions of the northern waters today continue into the early
night. Winds reduce overnight, but still remain hazardous for
small craft across most of the waters. Significant wave heights
of up to 11 to 12 feet in the outer waters north of Pigeon Point
continue into Saturday night with 6 to 10 feet elsewhere over the
open water. Seas begin to diminish towards the end of the weekend
and into next week.

&&

.CLIMATE...
Issued at 127 AM PDT Sat Jun 1 2024

Record high temperatures at the long term climate stations for
June 4th and 5th:

Station             June 4th             June 5th

Santa Rosa          98 in 1949           102 in 1926
Kentfield          101 in 1981           102 in 1926
Napa               102 in 1981           105 in 1903
Richmond            90 in 1955            86 in 1983
Livermore          105 in 1960           104 in 1926
San Francisco       92 in 1949            95 in 1883
SFO Airport         92 in 1955, 1949      89 in 1972
Redwood City       100 in 1981            97 in 2002, 1972
Half Moon Bay       71 in 1955            74 in 1958
Oakland downtown    96 in 1981            87 in 2002
San Jose            98 in 1904           100 in 1926
Salinas Airport     92 in 1949            87 in 1949
King City          102 in 1981, 1957     105 in 1926

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay-SF Bay N of Bay Bridge.

     Gale Warning until 3 AM PDT early this morning for Pt Arena to
     Pt Reyes 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 Monday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt
     Piedras Blancas 0-10 nm.
-- End Changed Discussion --

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...AC
MARINE...Murdock

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