000
FXUS66 KMTR 140349
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
849 PM PDT Sat Apr 13 2024

...New UPDATE...

.SYNOPSIS...
Issued at 102 PM PDT Sat Apr 13 2024

Rain showers and isolated thunderstorms will continue through the
overnight hours while shifting southward. Storm chances decrease
overnight, but showers linger into Sunday afternoon before dry
weather returns. A warming trend is then expected throughout the
upcoming week.

&&

.UPDATE...
Issued at 847 PM PDT Sat Apr 13 2024

Pretty interesting weather day around the Bay Area and Central.
Ample cloud cover, colder airmass/fropa, and precipitation led to
a rather chilly day. Temperatures maxed out in the 40s to mid 50s
with the highest peaks staying in the 30s. That`s about 15 to 35
degrees below seasonal average mid-April. In addition to the
chilly temperatures winds remained breezy to gusty at times out of
the south. The stronger winds gave an extra bite to the
temperatures and made it feel a little more raw. Currently some of
the hills around the region are sporting wind chilling values in
the mid 20s to low 30s.

As for precip, a solid band of precip rolled through earlier today
with the fropa. In its wake precip has turned more
showery/convective. More on this a little later... Rainfall
amounts over the last 24 hours are pretty decent with pre-frontal
precip yesterday evening/last night and the fropa today. Rainfall
amounts: 0.75-1.5" coastal mts with Anderson Peak above Big Sur
the winner at 2.33". Elsewhere, generally 0.20-0.75". As stated
above, the passing system brought in colder air. Snow levels
dropped last night and remained lowered for most of the day. As a
result, some of the higher peaks saw minor accumulations per
webcams.

Convective activity over the coastal waters...While there are
still thunderstorms in the official forecast there hasn`t been any
lightning observed. A few stronger cells came close earlier in
the evening, but not enough vertical development/ice in the
column for lightning production. CAPE (100-200 J/km) still
remains decent offshore, but meso-analysis shows a sliver of CINH
along the immediate coast. SST temps around 11C and observed
850mb temps around 0C-1C may not be enough differential to give
the stronger cells the boost they need. In fact, latest KMUX
radar is showing a more stratiform look with precip interacting
with the melting layer. All that being said, won`t take thunder
out of the forecast just yet, but we`ll be watching it closely as
stronger showers move onshore through early tonight.

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 102 PM PDT Sat Apr 13 2024

By this afternoon and evening we will transition to post frontal
rain showers and isolated thunderstorms as the atmosphere aloft
becomes more unstable. CAPE values are forecast to be between 200-
300 J/kg with little to no CIN. Any heavier showers and/or
thunderstorms will be capable of producing brief heavy rainfall,
gusty winds, copious amounts of small hail, occasional lightning,
and rapid onset of flooding. Thunderstorm potential will shift
southward tonight and diminish Sunday morning.

Lingering showers will be possible over the Central Coast through
Sunday afternoon with conditions clearing out by the late evening.
Temperatures will struggle to warm into the upper 50s near the coast
to low/mid 60s inland on Sunday (40s in the highest peaks).

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 102 PM PDT Sat Apr 13 2024

High pressure will begin to build in wake of the exiting weather
system and will allow for a warming and drying trend to resume. By
Wednesday and Thursday, expecting the interior to warm into the
upper 70s to lower 80s with upper 60s to mid 70s near the coast.
Friday and beyond, zonal flow sets up across the region allowing for
a few degrees of cooling across the interior and more so at the
coast with a likely return of a marine layer.

&&

.AVIATION...
(00Z TAFS)
Issued at 804 PM PDT Sat Apr 13 2024

MVFR-VFR. KMUX radar shows light showers over land and a bit more
widespread shower development over the coastal waters and offshore
waters closer to the low pressure system.

Vicinity of SFO...MVFR-VFR. Occasional showers and southeast to
east wind tonight and Sunday morning. Wind shifting to westerly
10 to 15 knots Sunday afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR. Showers and east to southeast winds
tonight and Sunday morning. Wind shifting to westerly 10 to 15
knots Sunday afternoon.

&&

.MARINE...
(Tonight through next Friday)
Issued at 220 PM PDT Sat Apr 13 2024

Breezy fresh to strong winds continue across the coastal waters
in wake of a frontal passage. The occasional near gale force
gust, particularly in the southern coastal waters, cannot be ruled
out through tonight. Showers and isolated thunderstorms will
impact the waters this evening and into the overnight hours before
diminishing in coverage on Sunday. Moderate period northwesterly
swell will continue to build through the waters through tonight
beginning its abating trend Sunday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday 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-SF Bay N of Bay Bridge.

     Small Craft Advisory until 9 PM PDT this evening for Pt Arena to
     Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to
     Pigeon Pt 0-10 nm.

&&

$$

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

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