278
FXUS66 KMTR 200427
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
927 PM PDT Sun May 19 2024

...New UPDATE...

.SYNOPSIS...
Issued at 1237 PM PDT Sun May 19 2024

Typical summer-like pattern to persist throughout the first half of
the week. Temperatures are forecast to dip below seasonal averages
by late week and into the upcoming weekend as an upper level trough
impacts the region.

&&

.UPDATE...
Issued at 927 PM PDT Sun May 19 2024

It`s clear except for patchy low clouds forming along coastal San
Mateo County and Santa Cruz County, including around the rest of
the Monterey Bay and northern Salinas Valley in northern Monterey
County. Satellite also shows a couple patches of low clouds over
southern Santa Clara County. The marine layer slopes from a depth
of a few hundred feet at Bodega Bay to 2,000 feet at Fort Ord. A
high pressure system is located 1,000 miles west of the Bay Area
and a 500 mb low pressure trough is over the western states. With
weak (and dry) surface low pressure over interior California, a
strong pressure gradient exists mainly over the coastal waters,
generating gales over the coastal waters. Point Arena buoy and
Bodega Bay buoy wind gusts have been near 40 knots, recently cold
water upwelling has lowered the sea surface temperature to 49F at
Point Arena buoy.

&&

.SHORT TERM...
(This evening through Monday)
Issued at 1237 PM PDT Sun May 19 2024

Clouds continue to rapidly erode as of early this afternoon and will
continue to do so into the evening. Low clouds are more than likely
to return to the Monterey Bay region and the San Francisco Peninsula
overnight but will clear by early-to-mid morning. Also, cannot rule
out patchy drizzle in and around the Monterey Bay early Monday
morning.

Afternoon temperatures for Monday will be similar to today, yet
coastal areas will warm by a few degrees thanks to northerly flow
across the region. Thus, expecting highs to range from the lower
60`s to near 70 degrees at the coast with mid 70`s to lower 80`s
across the interior.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 301 AM PDT Sun May 19 2024

A slight warming trend is expected through mid-week with
temperatures building into the upper 70s to mid 80s by
Tuesday/Wednesday. Inland stratus coverage is expected to be less
impressive this week as a deeper marine layer and gusty offshore
winds keep the atmosphere well mixed and low clouds confined to the
coast. Ensemble guidance agrees that Tuesday is looking to be the
warmest day this week with the highest probability of widespread
temperatures greater than 80 degrees. Minor heat risk begins to
spread through most of the Bay Area and portions of the Salinas
Valley Monday through Thursday. People who are incredibly sensitive
to heat should take precautions while outdoors and remember to drink
plenty of water.

By late week, upper level troughing strengthens and moves farther
south into California with an associated surface low passing through
the state. This will bring about a pattern change with widespread
below average temperatures expected. By the weekend, inland highs
will be in the upper 60s to mid 70s with coastal highs in the upper
50s to low 60s. CPC temperature outlooks have temperatures leaning
below average through the end of May and into the beginning of June.
Ensemble guidance suggests this system will be fairly dry for our
region with any precipitation associated with it directed northwards
of us into far northern California/southern Oregon.

&&

.AVIATION...
(00Z TAFS)
Issued at 602 PM PDT Sun May 19 2024

A weak and dry surface low pressure center over the northern
Central Valley is juxtaposed to an increasing pressure gradient
over the coastal and offshore waters. The ACV-SFO pressure
gradient is 6.7 mb and the SFO-SAC pressure gradient is 3.2 mb.
It`s VFR, however regionally it`s a complex surface pressure
pattern (winds) coupled to an evolving dynamic pattern involving
upper level troughing. The marine layer depth to the base of the
low level temperature inversion varies along the coast and will
vary greatly tonight and Monday morning with offshore winds
(downsloping, warming) over the North Bay to SF Peninsula while
locally onshore winds (upsloping, cooling - sufficient cooling to
erode the marine layer temperature inversion) over the South Bay
to the north Central Coast.

In the near term the HRRR output appears to have a better handle
(vs the NAM) on near surface humidity, it helps determine cigs vs
no cigs forecast. Monitoring the aforementioned surface low in
the Central Valley and its southward motion tonight and Monday,
the low will influence surface winds. For example surface winds at
KSJC are likely to shift over to southeasterly 5 knots increasing
to 8 to 10 knots 09z-17z Monday.

Vicinity of SFO...Peak wind gust to 37 knots 2355z prompted an
airport weather warning for gusty west winds until 04z (9 pm PDT)
this evening, more recent 5 min obs show the wind has subsided a
little bit. Strong NW winds over the northern coastal waters are
sweeping evaporated sea salt to the air resulting in hazy/haze
conditions, limiting surface visibilities to 5 miles /MVFR/ along
the coast. West wind at KSFO is periodically transporting haze
from the coast to the terminal. Otherwise VFR/MVFR tonight and
Monday, west wind easing overnight to less than 10 knots. West
wind increasing Monday afternoon and evening to 18 gusts 25 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Onshore winds 10 to 20 knots early, easing
overnight to 5 to 10 knots. It`s a complex forecast regarding cigs
tonight and Monday as described above this area will begin losing
its marine layer temperature inversion allowing for good vertical
mixing with drier air aloft, however upsloping, cooling may still
produce a sct-bkn cloud cover /MVFR/ best chances late tonight and
Monday morning. Cyclonic circulation/eddy circulation over the
Monterey Bay Monday morning may temporarily improve ceiling
development around sunrise, unless downsloping, warming, drying
across the Monterey Bay (from the Santa Cruz Mountains) is enough
to offset cloud development. Otherwise VFR Monday.

&&

.MARINE...
(Tonight through next Friday)
Issued at 450 PM PDT Sun May 19 2024

Buoy observations over the outer waters are beginning to show
wind gusts reaching gale force this afternoon. Strong northerly
winds and gale force gusts will be present over much of the waters
today and Monday, with only slight reductions in wind speed
during the overnight hours. Expect hazardous conditions and
steeper wind waves from these building winds throughout the next
work week. It is not until next weekend that winds are expected to
ease.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10
     nm.

     Small Craft Advisory until 3 AM PDT Tuesday for Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Gale Warning until 9 AM PDT Tuesday for Pt Arena to Pt Reyes 10-
     60 NM.

     Gale Warning until 3 AM PDT Tuesday for Pigeon Pt to Pt Pinos 10-
     60 NM.

&&

$$

UPDATE...Canepa
SHORT TERM...RGass
LONG TERM....Kennedy
AVIATION...Canepa
MARINE...Canepa

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