971
FXUS66 KMTR 022059
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
159 PM PDT Thu May 2 2024

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

.SYNOPSIS...
Issued at 119 PM PDT Thu May 2 2024

Warm weather continues through the day today and tomorrow
afternoon. Beneficial rain befalls the region late Friday and
through the afternoon of Saturday. Cool overnight temperatures
expected Sunday and Monday mornings. Dry conditions return Sunday
and last through next week.


&&

.SHORT TERM...
(This evening through Friday)
Issued at 119 PM PDT Thu May 2 2024

A look across the region at this hour shows many interior locations
already reaching into the low to mid 70s. Meanwhile closer to the
coast and bay shorelines, temperatures are in the upper 50s to low
60s. Temperatures will warm today into the high 70s away from the
coastline, with a select few locations maybe seeing temperatures
reach the 80 degree F mark. However, chances of reaching the 80
degree mark are fairly low even for the favored interior spots. Napa
appears to be the most highly favored for the chance to reach 80
degrees, but even then, with only a whopping 30% chance. Elsewhere
in locations such as Gilroy and Hollister, chances are only in the
20% range. Coastal locations will only see highs in the mid 60s at
best.

As upper level ridging builds and continues, temperatures are
expected to be largely similar tomorrow. Breezy northwesterly winds
in the afternoons will continue, but ease into the nighttime.

Late Friday night, rain begins to approach the region, impacting the
North Bay first, and then slowly making its way south. The previous
forecaster`s long term discussion still largely holds, so will
not reinvent the wheel. Will just mention that rain totals have
increased ever so slightly from the previous forecast, but not by
much. By a few hundredths generally. Descriptions in the long term
discussion still hold largely.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 119 PM PDT Thu May 2 2024

Seeing good global and mesoscale model agreement, one long wave
trough is now stationary along the West Coast, part of an unsteady
northern hemispheric long wave trough pattern. A low pressure
system from the Aleutian Islands will move through the long wave
trough and bring rain to our forecast area Friday night and
Saturday. Rain developing first over the North Bay Friday night,
rain quickly spreading southeastward across much of the rest of
the forecast area Saturday. Expect noticeably cooler temperatures
especially inland Saturday with daytime highs in the upper 50s to
mid 60s, warmest southern interior; daytime temperatures 5F to 15F
below early May normals. The low is still expected to brush by
and tap higher levels of water vapor extending far north of
Hawaii, while retaining a strong mid-latitude influence e.g. it`s
an appreciably cold core system up through the 700 mb level by
comparison on Oakland upper air climatology, the pool of cold air
a little more compact by the 500 mb level. Unlikely there`ll be
layer instability extending above 700 mb, forecast 700-500 mb
lapse rates are low and much more stable. Recent precipitable
water values on the GFS maintain between 1.00" and 1.10" Saturday,
not far from the max moving average on Oakland upper air sounding
climatology in early May.

Seeing some recent increases in model forecast rainfall amounts.
For example over 0.50" to 1" rain totals North Bay, near 0.50" low
elevations and up to 0.75" to 1" East Bay hills/mountains and the
Santa Cruz Mountains, 0.10" to 0.20" interior north Central Coast to
around 0.50" Big Sur Coast. The Bay Area and northernmost north
Central Coast may receive over half if not nearly May normal
precipitation from this system if current QPF verifies. As mentioned
expect wet and cooler weather Saturday, gusty northwest winds over
the coast temporarily subsiding with the passage of a surface cold
front/trough.

Chilly to cold overnight low temperatures for the time of year (40s
coastside and bayside / 30s inland) are forecast late Saturday night
to Sunday morning and Sunday night to Monday morning. San Francisco
and Oakland downtown possibly including a few other locations may be
nearing record lows Sunday and Monday mornings. Stay tuned to updates,
right now Sun-Mon mornings look to be the chilliest. Forecast temperature
guidance could edge a little lower between now and late weekend.

End of previous discussion.

Overall, this weekend`s system will bring beneficial, although
late-season rain. Late Saturday, rain begins to cease and a dry
pattern returns to the region with temperatures gradually warming
through the next week into the low to mid 70s for interior regions.
Despite gradual warming, CPC 6-10 day outlooks place much of
California in a below-normal temperature category, and below
normal for precipitation.



&&

.AVIATION...
(18Z TAFS)
Issued at 1142 AM PDT Thu May 2 2024

VFR prevails through the TAF period for the majority of terminals in
the region. Gusty W/NW winds will be the primary impact once more
today, with terminals seeing gusts generally in the 20-25 knot range
and sustained winds around 10-15 knots. Current thoughts are that
gusts should diminish towards the 04-06Z hours for most terminals,
with sustained winds easing to below 10 knots towards midnight.
Stratus will hug the coastline tonight, but is not expected to
advect inland thanks to ridging helping to squash cloud decks and
prevent them from being able to cross the coastal mountain barrier
in many locations, with the exception of KMRY.


Vicinity of SFO...VFR through the TAF period, with W/NW winds
strengthening into the afternoon to become strong around 25 knots
sustained, and gusting to around 32-34 knots at the strongest. Time
of peak winds towards 00Z this evening, but gusts quickly decrease
towards 04Z. Confidence on gusts remaining below 35 knots is
moderate. A FEW-SCT low clouds may filter into the SFO terminal in
the early to mid morning of Friday, but low confidence on any CIGs
developing. Moderate to strong onshore winds return Friday
afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR prevailing through the early evening,
with moderate onshore winds gusting to around 25 knots in the late
afternoon. Low clouds will begin to push into the terminal space
towards the later evening, bringing MVFR CIGs, just on the cusp of
becoming IFR. Into the early morning of Friday, CIGs are expected to
lower to become predominantly IFR and lasting through at least
sunrise of Friday.

&&

.MARINE...
(Today through Tuesday)
Issued at 841 AM PDT Thu May 2 2024

Strong winds persist throughout Friday, with gale force gusts of
40 to 45 knots possible. Strong winds will result in hazardous
seas and steep wind waves with significant wave heights reaching
10 to 13 feet in the outer waters. Conditions gradually improve
over the weekend and into next week as winds begin to ease. Rain
chances begin early Saturday as a trough descends over the region.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT this afternoon for Mry Bay.

     Gale Warning until 9 PM PDT this evening for Mry Bay.

     Gale Warning until 9 PM PDT this evening 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-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning until 3 AM PDT Friday for Pigeon Pt to Pt Pinos 0-
     10 nm.

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

&&

$$

SHORT TERM...AC
LONG TERM....Canepa/AC
AVIATION...AC
MARINE...RGass

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