NWS San Francisco Bay Area, CA wrote its last area forecast discussion before the first event at Mar 22, 7:57 PM PST, 50 minutes earlier.
Area forecast discussion, Mar 22, 7:57 PM PST, 50 minutes before
Area Forecast Discussion
National Weather Service San Francisco Bay Area
857 PM PDT Wed Mar 22 2023
.SYNOPSIS...Scattered light showers persist but are gradually
diminishing. Dry and cooler weather is forecast for the end of
the week and weekend, with cold overnight temperatures and frost
possible both Saturday and Sunday mornings. The next Pacific storm
is forecast to approach the California Coast for late Monday and
into Tuesday.
&&
.DISCUSSION...as of 08:57 PM PDT Wednesday...The center of the
low is currently over the coastal border of Monterey and San Luis
Obispo Counties, slowly drifting southward. Over the last 24
hours, much of the eastern portions of the Bay Area and the
Central Coast saw a quarter of an inch to a half an inch, while
coastal areas saw three fourths of an inch to just over an inch.
Naturally the Santa Cruz Mountains and the Santa Lucias had the
highest totals due to orographic lift and being on the southern
periphery of the low. These higher terrains recorded an inch and a
half to over two inches were measured. There are still showers
persisting from Alameda County southward through Monterey County,
but the overall strength of the cells have diminished with the
setting sun. As such, all Flood Warnings and Advisories that had
been issued during the day have since been expired. Scattered
showers are forecast to linger in the overnight hours, but there
is high confidence that rain rates should be fairly light. The
radar will remain in precip mode and will be monitored through the
night in case anything changes.
As the low drops southward, prevailing northwest wind flow has
returned. Cold air advection will usher in a steady stream of cooler
air tonight and through the weekend. There is still plenty of
scattered clouds over the area, as observed on satellite, but if
that were to clear out and allow more radiational cooling, there
may be patchy fog that could develop with the cooler temps
Thursday morning. There is low confidence in that forecast given
how slow the center of low pressure is moving southward, which
should keep scattered clouds around the Bay Area through the
night. However, there is growing confidence in the cooler air
dropping temperatures later in the week. There is a chance for
some patchy frost development on Friday morning with higher
likelihood over the weekend. Now is the time to protect any
outdoor plants.
With Monday being so far away, there is still a tremendous amount
of uncertainty with the next rain event regarding timing,
location, and overall magnitude of impact. Current indications is
that it will be more frontal in nature extending from a center of
low pressure that will bring another round of rain early next
week, potentially by Monday afternoon. Coastal areas will likely
see the higher amounts than the traditional rain shadowed interior
areas. To date, models have been fluctuating between higher
amounts to lower amounts and back again, and early returns on the
recent run of the blend of models looks like the pendulum will
swing back toward increasing the rain totals, yet still keeping it
weaker than this past event for the time being. Considering that
Thursday and Friday this week looks to be drier, it would not hurt
for anyone to review their "go bag" and make sure that supplies
like batteries, dry goods, bottled water, etc. are up to date. We
will all hope for a weaker system, but being prepared is key.
&&
.PREV DISCUSSION...As of 2:20 PM PDT Wednesday...
Today...Low pressure system continues to spin off the coast and
has drifted southward slightly with the center of the low now over
the Monterey Bay. The low has weakened substantially in the last
24 hours, where the minimum pressure is now 1008 mb compared to an
anomalous 985 mb reading yesterday afternoon. This is good news
for our area as shower activity continues to diminish this
afternoon. Showers that we do see on radar continue to spin
counterclockwise around the core of the low and will persist
through the afternoon as low continues to weaken and drift south.
An additional few hundredths of an inch to up to 0.10" possible
through the early evening, mainly staying confined to the Central
Coast.
Also seeing rivers and streams in the Bay Area receding in response
to reduced shower activity, allowing for the expiration of some
flood warnings and advisories in the area, including the Flood
Warning that included Half Moon Bay. Flood Advisories continue for
the Santa Cruz Mountains, the Monterey Bay coastal region, and
southern Santa Clara County with some creeks still showing
elevated levels, such as the Uvas Creek south of Gilroy and some
creeks in Sonoma County, but it appears they have crested and
will be receding shortly or have already begun receding. Some
minor, lingering flooding issues possible along roadways through
the afternoon.
Thurs/Fri...Dry weather expected for the end of the work week.
However, we remain in a troughy pattern, which means unsettled
weather and colder than normal temperatures continue. Luckily for
the next few days, not expecting moisture to be associated with the
next frontal passage, which will move through the Bay Area Thursday
afternoon through Friday morning. From this cold front, we can
expect some gusty NW winds Thursday afternoon into Friday with gusts
around 20-25 mph with localized gusts up to 35 mph near the coast
and at higher elevations. It will be a nice break from the wet
weather, but keep in mind that it will still be windy and chilly if
you plan to be outdoors!
This weekend..Saturday during the day will remain windy in the post-
frontal environment with wind gusts of 20-30 mph expected around the
region. Winds diminish overnight Saturday into Sunday. With colder
airmass over our area in addition to winds easing up and skies
clearing out, expecting cold morning temperatures. Fri night into
Sat morning as well as Sat night into Sun morning look to have
temperatures in the interior regions of our area in the low to mid
30s. Coldest temps expected Sunday morning with highest probability
of reaching freezing temps is for interior Sonoma County valleys,
where NBM has a roughly 40 to 60% probability of lows dipping
below to 32 degF or colder. Elsewhere, lows will still be in the
mid 30s these mornings.
Mon/Tues..Our attention turns to the next potential storm system.
It's still too early to know the details, but ensemble guidance
showing strong upper low moving through the Pacific NW/NorCal
regions Mon night into Tues, which could bring more heavy rain
and strong winds. Will continue to monitor closely.
&&
.AVIATION...As of 4:20 PM Wednesday....For the 00Z TAFs.
Generally VFR with conditions dropping to MVFR-IFR within the most
intense showers. Shower activity decreases through the day as the
surface low moves southward, with low to moderate confidence
(around 30-40% probability) of clearing skies. If skies clear out,
expect patchy valley fog overnight, clearing in the morning.
Winds will be light to moderate, with a northwesterly pattern
building as the surface low leaves. A moderate-high confidence
(60-70% probability) of generally VFR conditions through Thursday,
with a cold front moving through the region that day providing a
possibility of lower ceilings.
Vicinity of SFO...VFR with northwesterly winds through the TAF
period. Winds will be quite breezy, around 12-15 knots, throughout
the TAF period. A low to moderate confidence (30-40% probability)
of IFR conditions developing Thursday evening with a cold front
moving through the region.
SFO Bridge Approach...Confidence slightly higher for low ceilings
Thursday evening over the southern San Francisco Bay.
Otherwise similar to SFO.
Monterey Bay Terminals...High confidence (80-90% probability) that
MVFR develops at MRY this evening, with confidence somewhat lower
(60-70% probability) of MVFR developing at SNS. Ceilings start to
lift around 18Z. Winds remain light for the rest of today before a
breezy northwest flow develops Thursday morning.
&&
.MARINE...as of 08:55 PM PDT Wednesday...A surface low near Point
Piedras Blancas continues to drift to the southeast and weaken. A
mainly dry cold front rapidly approaches and passes across the
coastal waters and bays late Thursday into Thursday night. A
moderate northwest swell moves in over the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Coastal Flood Advisory...CAZ006-505-506-508
SCA...Mry Bay
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
&&
PUBLIC FORECAST: SMM/DK
AVIATION: DialH
MARINE: DialH
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