Altadena, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

235
FXUS66 KMTR 250420
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
920 PM PDT Thu Apr 24 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1217 PM PDT Thu Apr 24 2025

Cool and cloudy conditions will grip much of the Bay Area and
Central Coast through the first half of the weekend. There`s an
opportunity for light rain and a rumble of thunder or two, late
Friday and into Saturday. The favored regions for rain and
isolated storms will be across the Central Coast and adjacent
offshore waters. Thereafter, rain-free conditions are forecast.

&&

.SHORT TERM...
(This afternoon through Friday Night)
Issued at 1217 PM PDT Thu Apr 24 2025

Short Term Key Messages
-Cool and cloudy conditions persist
-Rain chances increase late Friday

The marine layer has established itself across the region and it`s
quite a stark contrast from 24 hours ago. Widespread cloud cover
has been noted on the latest satellite presentation, though inland
areas and regions of terrain are clearing very gradually.

With broad mid-level troughing encouraging more in the way of
onshore flow, I anticipate clearing will be short lived and for
some regions, especially along the coast, mostly cloudy skies will
prevail. We`ll be locked into this onshore flow regime through at
least Saturday, and the forecast will remain on the cool side as
a result. As it pertains to rain chances, it appears that a bulk
of the "heavier" precipitation won`t arrive until after 00 UTC
Saturday or 5pm Friday. Prior to that, pockets of drizzle are
forecast with perhaps a few areas measuring a few hundredths of an
inch. If the forward speed of the upper system accelerates, then
more widespread rainfall will be on the table earlier in the
evening on Friday.

&&

.LONG TERM...
(Saturday through next Wednesday)
Issued at 1217 PM PDT Thu Apr 24 2025

Long Term Key messages
-Rain and isolated thunderstorms forecast
-High elevation snow (Santa Lucia and Diablo Ranges)
-Warmer and largely rain-free Sunday onward

The main upper low will pinwheel just west of the Southern
California Bight on Saturday. Forecast 700-500mb lapse rates
should approach 7 to 7.5 C/km across the marine areas and
southern Monterey County beneath the cold pocket associated with
the upper low. This translates to a few hundred joules/kg of CAPE,
though the max CAPE resides across SLO and points southward. The
positioning of the low does modulate the thunderstorm risk. If the
low slides more to the south, then the pocket of cooler air aloft
will be farther displaced from our area, thereby lowering the
isolated thunderstorm risk. If the upper low remains a bit farther
north, then a greater portion of the Central Coast will be at a
greater risk for isolated storms. Currently the primary hazard
would be isolated lightning strikes. Brief accumulating hail
cannot be discounted, especially with any of the more vigorous
showers and/or storms.

Overall, rain amounts will be beneficial, especially across the
Central Coast. This area largely missed out on some of the more
robust AR events from this past year and this rain will at least
mitigate the fire weather threat initially. Rain amounts will be
quite respectable, given the time of year and amounts will average
between a few tenths of an inch to perhaps as great as 1/2 inch.
In fact there`s around a 50% chance that some parts along the Big
Sur Coast/Santa Lucia Range may see between 1/2 to 3/4 of an inch
of rain.

But wait...there`s a little bit more. Some of the higher peaks of
the Santa Lucia and Diablo Ranges may even get a bit more than
"novelty" snowflakes as blended guidance suggests around a 50%
chance for 2" of snow. At this time, no plans for any winter
headlines as snow will be across a very confined to the highest
peaks, but if snow levels come in a little lower, we may need to
consider stronger messaging/wording.

Saturday evening through the remainder of the extended forecast
appears that it`ll remain quiet. This is supported with agreement
among the various model solutions with ridging taking shape.
Moreover, longer term model predictions support odds leaning
toward warmer and drier than normal conditions precip.

&&

.AVIATION...
(06Z TAFS)
Issued at 909 PM PDT Thu Apr 24 2025

Mixed bag of MVFR and VFR cigs through out the TAF period as a
weak upper low meanders along the West Coast. Expecting at least
SCT conditions throughout period with cigs lifting slightly later
in the period as the surface trough and rain showers move through
the region. Complicated rain forecast for the next couple of days
as we will be in a very moist, onshore flow, on-again-off-again
shower regime. Not expecting any prolonged IFR due to showers, but
can`t rule out a very brief heavy shower causing decreased vis,
especially later in the period.

Vicinity of SFO...Expecting to toe the line between MVFR/VFR cigs
throughout the TAF period with some low-level clearing expected
during the afternoon (mid-level cigs remain). The aforementioned
complicated rainfall timing forecast ultimately lead to the
decision to keep such a long prevailing group at the end of the
TAF period. No notable change that can be forecasted with any
confidence during the last period of the TAF.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Cigs likely to persist through the
period. VFR now, but will likely lower to MVFR overnight tonight.
Some low-level clearing Friday afternoon as widely scattered rain
showers move in. Mid-level cigs expected to begin to lower again
at the end of the TAF period as the center of the upper low
approaches the Central Coast. Rain chances increase just after the
current TAF period.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 909 PM PDT Thu Apr 24 2025

Light showers enter the forecast late Friday morning across the
waters, with the best chances late evening into Saturday morning.
Slight chance of isolated thunderstorms for waters generally south
of Pigeon Point. Strong breeze and rough seas return across the
waters late Saturday. Dreary conditions linger into Sunday
morning before drier conditions set for next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Behringer
MARINE...Behringer

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