Portola Valley, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

287
FXUS66 KMTR 271605
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
905 AM PDT Sun Apr 27 2025

...New UPDATE, MARINE...

.SYNOPSIS...
Issued at 1205 AM PDT Sun Apr 27 2025

Light showers focused on the Central Coast continue through the
morning. A pattern change will bring warmer and drier weather
through the work week.

&&

.UPDATE...
Issued at 904 AM PDT Sun Apr 27 2025

Drizzly conditions and light rain showers continue across the Bay
Area and Central Coast through this afternoon. A look at 36 hour
precipitation totals shows the Santa Lucia Range as the big winner
with between 0.3"-0.6" observed from this event. Elsewhere, totals
ranged from a few hundredths of an inch to two tenths of an inch
with locally higher amounts across the elevated terrain. Additional
rainfall today is expected to be light, amounting to only a few
hundredths of an inch.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1205 AM PDT Sun Apr 27 2025

KMUX shows light rain falling throughout the majority of Monterey
County. This includes the Big Sur International Marathon course
where runners will begin loading shuttles in just 3 hours or so. A
nearly cut-off low pressure system has drifted towards the CA/NV
border, and the Bay Area is now firmly in the back-side
environment. The dynamics are a bit unusual, however. A moisture
plume is keeping the PWAT above 150% of normal, despite the
northerly winds which veer offshore with height. There is also
some indication of frontogenesis with warm air advection present
at 700 mb. Thunderstorms never materialized on Saturday, and the
chance continues to diminish. All signs point to the rain tapering
off through the morning with skies starting to clear in the
evening. Temperatures will remain in the 50s and 60s due to
overcast skies and a lingering cold air mass. There is a good
chance for fog during the Monday commute as building high pressure
causes the skies to clear over the still cool and humid surface.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 1205 AM PDT Sun Apr 27 2025

After any fog mixes out late Monday morning, it will turn into a
beautiful day with plenty of sunshine and temperatures up to 10
degrees warmer than the weekend. The good weather will continue
through the work week as a ridge builds over the west coast. Mid
week looks to be the warmest with inland highs in the mid to upper
70s. A shallow marine layer will keep coastal areas in the low
60s, but the coastal clouds shouldn`t last all day. Most guidance
indicates the pattern will become unsettled again by Friday or
Saturday as some combination of a cut-off low and/or mid-level
trough bring back overcast skies, cooler temperatures, stronger
wind, and a slight chance for rain next weekend.

&&

.AVIATION...
(12Z TAFS)
Issued at 517 AM PDT Sun Apr 27 2025

Surface observations primarily report MVFR with occasional IFR
conditions, along with a few lingering areas of light rain. A few
fog patches /LIFR-IFR/ may still have time to develop through
daybreak. Later in the morning and early afternoon ceilings should
gradually lift except along the immediate coastline from San
Francisco Peninsula to the north Central Coast a surface to near
surface cool front will arrive which may result in additional
MVFR-IFR ceilings along with spotty light drizzle or very light
rain with the benefit from upsloping winds. Currently 2.3 mb SMX-SFO
and 1.4 mb SBA-SFO pressure gradients (southerly wind direction)
are juxtaposed to a similar but oppositely directly 1.9 mb ACV-SFO
pressure gradient; the southerly gradients decrease later today
and tonight. SFO-SAC gradient is currently near flat. With a high
distribution of water vapor from the surface through the lower levels,
cool air nearest the ground including plentiful clouds and air near
saturation in the lower levels still could take a while for the
clouds to lift under late April sun.

Tonight and Monday morning HREF output shows MVFR-IFR redeveloping.

Vicinity of SFO...MVFR. West wind 5 to 15 knots today and tonight,
becoming light and variable by Monday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR-IFR. Winds becoming westerly 10 to
15 knots by late morning. As mentioned earlier in the aviation
discussion, a shallow cool front arrives per recent NAM output and
this may keep low clouds and spotty light precipitation going a
little longer today. Low clouds /MVFR/ tonight and Monday morning.
Light west winds tonight and Monday morning.

&&

.MARINE...
(Today through Friday)
Issued at 904 AM PDT Sun Apr 27 2025

Northwest winds will be gusty due to a high pressure system
building over the offshore waters through early week, winds will
also result in hazardous seas across the outer coastal waters.
From mid to late week surface high pressure will gradually weaken
while an upper  level trough will move in from the northwest. By
late week another upper level trough from the northwest will
approach the coastal  waters and bays.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay.

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

     Small Craft Advisory from 3 PM to 9 PM PDT Monday for Pt Arena
     to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

     Small Craft Advisory until 9 PM PDT Monday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Canepa
MARINE...RW

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