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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KMTR 121857 AAA
AFDMTR

Area Forecast Discussion...UPDATED
National Weather Service San Francisco CA
1157 AM PDT Fri Apr 12 2024

...New SYNOPSIS, SHORT TERM, AVIATION, MARINE...

.SYNOPSIS...
-- Changed Discussion --
Issued at 1145 AM PDT Fri Apr 12 2024

Cooler and cloudier for today as highs fall back into average
range as the next rain-maker nears. Expect winds to increase into
the 15 to nearly 20 mph range with gusts of 25 to 40 mph by
Saturday morning. Showers are forecast to arrive after sundown
Friday with widespread showers across the Bay Area and Central
Coast by mid-morning Saturday. Saturday afternoon will feature a
renewed batch of showers with an increasing potential for
thunderstorms. Storms may produce bouts of small hail. Showers
linger through early Sunday afternoon across interior sections.
After a noteworthy cool down this weekend, a warming trend will
ensue next week.
-- End Changed Discussion --


&&

.SHORT TERM...
-- Changed Discussion --
(This afternoon through Sunday Evening)
Issued at 1145 AM PDT Fri Apr 12 2024

The forecast remains on track with just a few minor alterations.
As noted above, showers are forecast to arrive after sundown
Friday across the North Bay, though some light sprinkles or patchy
drizzle cannot be discounted along the coastal regions,
particularly down along the Big Sur.

Satellite imagery late this morning shows the first vestiges of
our upper level low now impinging on portions of the North Bay in
the form of high cirrus. We`ll turn our attention back to this
feature shortly. Pesky stratus farther south across the SF
Peninsula and Central Coast continues to gradually erode, though
some areas across the Santa Cruz Coast and Monterey Bay region
will stay completely socked in until later this afternoon. For
regions that get to experience the sunshine, enjoy it, as this
weekend will turn rather unpleasant for outdoor activities.

The latest short term and even coarser guidance for our next round
of rain/storms has come into really solid agreement regarding the
timing of precipitation. Overall, rainfall amounts remain
consistent with earlier forecasts. Even looking at the spread
between the lower QPF rain amounts and worst case scenario yields
only a 0.75 inch difference for most areas (a little higher for
the mountainous terrain). All in all, most of the inland areas can
anticipate up to 0.75 inches of rain, with coastal areas
averaging between 0.75-1.25 inches of rain. The big winners, rain
amount wise, will be the Santa Cruz Mountains, Santa Lucia Range,
and the Big Sur Coastline where 1.25-2 inches of rain are
forecast. The chances of exceeding 2.5 inches over a 72 hour time
period for the higher terrain east of California HWY 1 are around
30%. Regardless of exact amounts, pockets of moderate to briefly
heavy rainfall will result in ponding and some rises on area
creeks, rivers, and streams---though most of this rainfall should
be beneficial and not result in flooding. However, the potential
for slides will increase, especially across the Santa Cruz
Foothills/Mountains and across the Big Sur coastline.

Non-convective winds will increase as the low level height/surface
pressure gradients tighten. Southerly winds will increase later
today and into Saturday and the chances of seeing wind gusts of
over 25 mph ranges from near 50-60% across the North Bay to over
75% for the other areas. The potential to exceed 35 mph wind gust
really becomes confined to the higher terrain (Santa Cruz
Mountains, East Bay Hills, Diablo and Santa Lucia Ranges) and
along the coast (Monterey Bay and Big Sur). The chances to exceed
35 mph in these areas ranges from near 50-80%. Winds are forecast
to abate through the day on Sunday. Areas across the immediate Big
Sur Coast (near and just north of Point Sur) will be the windiest,
with chances for winds to top out between 40-45 mph around 40%.

Finally, the opportunity for isolated thunderstorms exists on
Saturday afternoon and evening. After the initial band of
precipitation late tonight into Saturday late morning exits to the
east, partial clearing may aid in destabilization. With CAPE
values forecast to increase to around 200 J/kg and mid-level lapse
rates approaching 8 C/km, there will be a potential (20-25%) for
vigorous showers and isolated thunderstorms. Showers and storms
will be mostly capable of producing copious amounts of small hail,
which may result in brief hazardous driving conditions due to hail
accumulation on Saturday afternoon and evening. Certainly don`t
be fooled by clearing skies earlier in the morning as this may
increase the chance for an afternoon shower or storm with hail at
your location. Some of the short term guidance this morning DID
increase PoPs Saturday afternoon and into Saturday evening,
particularly across the South Bay, Santa Cruz, Monterey, and San
Benito counties. Make sure you remain weather aware tomorrow
afternoon.

Lingering showers with a thunderstorm or two are forecast through
early Sunday with pleasant conditions thereafter. We`ll have more
on the nicer weather in the long term forecast a bit later on
today.
-- End Changed Discussion --

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 421 AM PDT Fri Apr 12 2024

The weekend will see the cold front`s parent low focusing over the
Bay Area and Central Coast, providing scattered showers and storm
chances through Saturday, with some lingering showers into Sunday.
Storm chances will peak around 25% into Saturday evening and into
the early night, with the focus being off the coast of Santa Cruz Co
and the Monterey Bay.

While the cold front will offer most of the weekend rain fall, the
shower and storm activity behind will add up over time.

As of the current forecast, Rainfall totals from Friday through
Sunday afternoon look to range from:

-0.4" to 0.75" for most inland areas
-0.75" to 1.25" for coastal areas and higher elevations in the North
Bay
-1.25" to 2" Santa Cruz Mtns and the Santa Lucias.
- above 2" for the highest peaks along the Big Sur Coast

A ridge pattern builds in quickly behind the weekend`s rains,
allowing for dry weather to return into next week. This will also
put the region into another warming trend with widespread 60 and 70
degree highs expected in the middle of the work week.

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 1145 AM PDT Fri Apr 12 2024

A mix of VFR and MVFR at the present time, with a brief window of
VFR at most sites by 20-21 UTC this afternoon. Increased winds
(becoming more southerly) are forecast this afternoon with
sustained winds near 10-15 knots and gusts in the 20 to 25 knot
range. The timing of -SHRA has been updated for the latest trends
in obs and model guidance. At this juncture, a band of SHRA will
overspread North Bay TAFs between 04-07Z on Saturday and the
remaining aerodromes between 07Z-10Z Saturday. MVFR will accompany
precip along with potentially higher westerly wind gusts closer to
30 knots.

Vicinity of SFO...Cigs continue to lift late this morning and by
21 UTC, I expect our brief window of VFR to prevail until later
this evening. SW`ly wind gusts near 25 knots are forecast for
this afternoon, with a potential that gusts subside below 20 knots
ahead of the band of -SHRA approaching from the west. For
simplicity sake, we`ll carry 25 knot gusts through much of the
period. Confidence in prolonged MVFR stratus prior to 06 UTC
Saturday isn`t high, but there are some indications that
intermittent MVFR is warranted a few hours before. Confidence is
medium to high with regard to SHRA timing. As noted above, a brief
3-4 hour westerly wind shift around 09 UTC Saturday may accompany
SHRA and we may advertise this in a TEMPO group in later
issuances. The chances for IFR remain below 30%, so for now we`ll
omit this from the TAF. There could be a brief lull in precip
later Saturday, but confidence in the timing is too low.
Instability does build tomorrow afternoon, and inclusion of VCTS
(also approaching from the west) may be warranted in future TAF
issuances.

SFO Approach Bridge...Similar to SFO.

Monterey Bay Terminals...MVFR cigs continue to plague MRY and SNS
with VFR not returning until closer to the 20-23 UTC time frame.
VFR will be very temporary with MVFR cigs returning just prior to
midnight Saturday. SHRA will approach MRY initially as a band of
precip approaches from the west. The SHRA coverage is forecast to
diminish briefly late morning and into the early afternoon. While
beyond the valid time period for this TAF set, another round of
SHRA, potentially with embedded TS, may be needed for Saturday
afternoon.
-- End Changed Discussion --


&&

.MARINE...
-- Changed Discussion --
(Today through Wednesday)
Issued at 1101 AM PDT Fri Apr 12 2024

Moderate to fresh northwesterly breezes will continue through this
morning. During the afternoon and evening hours, winds will
strengthen to fresh to strong and transition southwesterly ahead
of an incoming low pressure system. This system will bring rain,
near gale force gusts, and a 20% chance for thunderstorms to the
coastal waters through Saturday. A chance for occasional gale
force gusts remains possible particularly in the southern coastal
waters. Moderate period northwesterly swell will continue through
the weekend.
-- End Changed Discussion --

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 3 PM PDT
     Saturday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon
     Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10
     nm.

     Small Craft Advisory from 9 AM to 3 PM PDT Saturday for Pt Arena
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 PM this evening to 3 PM PDT Saturday
     for Pt Reyes to Pigeon Pt 0-10 nm.
-- End Changed Discussion --

&&

$$

SHORT TERM...Bain
LONG TERM....Murdock
AVIATION...Bain
MARINE...RGass

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