Brisbane, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

702
FXUS66 KMTR 241832
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1132 AM PDT Thu Apr 24 2025

...New AVIATION...

.SYNOPSIS...
Issued at 1239 AM PDT Thu Apr 24 2025

Cooler trend continues today into the weekend. Patchy drizzle and
fog are possible within the marine layer clouds. Light rain,
drizzle, and isolated thunderstorms are possible throughout the
region Friday and Saturday.

&&

.UPDATE...
Issued at 945 AM PDT Thu Apr 24 2025

The short term forecast is in good shape with little to no changes
needed. The marine layer remains entrenched across the region with
widespread low stratus. Interestingly enough, mist/fog has been
largely confined to the coast. Similar conditions are anticipated
Friday, with an increasing probability of rain activity this
weekend. We`ll have more details on that this afternoon.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1239 AM PDT Thu Apr 24 2025

Marine layer stratus has developed across the Bay Area and Central
Coast. The latest data from the Point Sur profiler suggests that the
marine layer has thickened to around 2500-3000 feet, a depth that
would support stratus intrusion well into the interior. Some of the
far interior locations could see some transitory sunshine for a few
hours in the afternoon, but the coastal region and the coastal
valleys should remain socked in through the day.

A cooling trend continues across the region with a strengthening
upper level trough approaching California. High temperatures range
from the lower to middle 60s in the inland valleys, with southern
Monterey County seeing temperatures up to the lower 70s, while the
coasts and the bays see temperatures reach the middle 50s to the
lower 60s. Onshore winds this afternoon will be breezy and gusty,
with gusts of 20-30 mph at the coast and through the gaps and
passes. In some favored regions, particularly Altamont Pass, Pacheco
Pass, and the Mayacamas, the gusty winds could last well into the
evening.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 1239 AM PDT Thu Apr 24 2025

An upper level low should impact the state on Friday and Saturday,
with the trends for a stronger and more southerly low continuing as
of the latest model outputs. The ensemble model clusters are finally
coming into agreement on the location of the low coming in, if not
the exact strength. As a result, while we`re more confident in where
the rain will fall, there`s still some variation in the exact rain
amount. The current forecast calls for around 0.10-0.25" of rain in
the Monterey Bay region, the Santa Cruz Mountains, and the Salinas
Valley, with rainfall totals as high as 0.5-0.7" in the Santa Lucia
mountains. Elsewhere, rain totals across the Bay Area will be very
light, especially across the North Bay where upper level offshore
flow will limit the precipitation chances, and outside of the
southern and eastern mountains of Santa Clara County, wetting rains
(over 0.1" of rain) are not likely.

We`re also noting an steady increase in the likelihood of
convection across the region. While still slight, the
probabilities of thunderstorms have risen to 10-20%, mainly across
the Central Coast, extending from Friday night through Saturday.
From the previous forecaster: Forecast soundings show a few
hundred J/kg of CAPE across the Central Coast overnight Friday
into Saturday with forecasted CAPE values to peak Saturday
morning. To have a thunderstorm you need four main ingredients:
moisture, instability, lift, and wind shear (speed or
directional). With this system incoming, we have a source of
moisture, a source of lift (cold frontal passage), and some
instability forecast. The questionable ingredient is wind shear.
As of right now during the time of the highest thunderstorm
probabilities (5AM-5PM Saturday), forecast soundings show some
directional wind shear (winds veering with height indicating some
warm air advection is occurring) but not very much speed wind
shear. The surface to 500 mb bulk shear shows much higher speed
shear values located just to our south in San Luis Obispo County
(NWS Los Angeles` CWA). While the current trend for this cut-off
low has been to shift southwards, if the low were to shift just
slightly northward we could potentially see those higher bulk
speed shear values shift into Monterey County. If this were to
occur, it would increase confidence that we may see some
thunderstorms across southern Monterey County given the alignment
of wind shear with our area of moisture, lift, and instability.
It`s worth watching over the next few days to see where this cut-
off low tracks (further south or further north) and how our
thunderstorm risk along the Central Coast changes this weekend.

Ridging should return after the trough moves out, with daytime highs
rebounding to near to slightly above the seasonal averages in the
early and middle part of next week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1057 AM PDT Thu Apr 24 2025

MVFR cigs are expected to persist through most of the forecast
period with increased chances of VFR late in the period by mid-
morning Friday with an increase in mixing as the upper level low
continues to approach from the north. Expect periods of drizzle
along coastal sites tonight through early Friday morning as well.
Breezy to gusty onshore flow will also increase as the upper
level system approaches.

Vicinity of SFO...MVFR is expected to prevail through the
forecast, however there is a chance of enough mixing for a window
of VFR conditions this afternoon into early evening. Onshore
winds will increase this evening becoming breezy as the upper
level low approaches from the north. VFR chances increase toward
the end of the TAF period late Friday morning.

SFO Bridge Approach...Similar to SFO

Monterey Bay Terminals...Expecting MVFR cigs to persist through
the forecast period. There is a chance for VFR conditions this
afternoon into the early evening, however current trends show a
steady fetch of moisture rich onshore flow limiting that
possibility. Patchy fog and drizzle are possible later tonight
through Friday morning as well.

&&

.MARINE...
(Today through Tuesday)
Issued at 945 AM PDT Thu Apr 24 2025

Expect quiet weather for the rest of today with some light rain
moving across the waters starting Friday morning and lingering
into that night. Strong northwesterly breezes and rough seas
return late Saturday.

&&

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

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...Murdock

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