Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 262354
Area Forecast Discussion
National Weather Service San Francisco Bay Area
454 PM PDT Sun Mar 26 2017
.SYNOPSIS...A weak weather system will spread light rainfall to
most of our region later the afternoon into the overnight hours.
Showers will mostly end by Monday morning. Expect decreasing
clouds on Monday with brisk afternoon and evening northwest winds.
High pressure will build back to our region and provide warmer
days on Tuesday and Wednesday along with fewer clouds. A system
will move to our east on Thursday and bring windier conditions
along with colder temperatures.
.DISCUSSION...as of 2:00 PM PDT Sunday...Multiple minor updates
to the forecast today to try to get the timing down as a weak
system will move through later. This morning KMUX was indicating
possible light rain, however no tips of the buckets were noted, so
now appears it was either just clouds or virga. Anyway, main band
of rain associated with the system is still forecast to go
through over the next 6 to 12 hours and bring light rainfall to
most parts of our CWA. Timing has it moving to the North Bay late
this afternoon, to SF Bay by early in the evening, and down to
Monterey Bay by mid-evening. Rain will switch over to showers
behind the front with precipitation possible overnight. Totals
still look like 1/4" to 1/2" for the North Bay Mountains, 1/10" to
1/4" for the rest of the North Bay plus the SC Mountains, with
less than .15" for the remainder of the CWA.
Breezy northwesterly winds can be expected on Monday as a ridge of
high pressure begins to build back into our region. Highest values
should be along the coast and coastal ranges. Winds will start to
abate by the evening as the gradient slackens. Tuesday and
Wednesday are shaping up to be quiet weather days with the ridge
in place. Temperatures will return to the 60s and 70s. A few lower
80s are not of out the question in Monterey County on Wednesday.
The pattern will change again on Thursday as an inside slider
moves into the intermountain region. Biggest question for a few
days has been if the low will be far enough west to produce
showers or if it will stay more to the east. 12Z operational and
ensemble forecasts are trending farther to the east and now favor
drier solutions. Still could be a few showers over the North Bay
Mountains and East Bay Hills, so those were kept in the forecast.
The bigger impact will be another round of cooler
temperatures(highs mostly upper 50s to upper 60s) along with
breezy conditions. 925 MB speeds off to the ECMWF are forecast to
be up to 40 KT at the coast. Those values will likely increase
with the higher resolution models as it gets closer.
The ridge will rebuild starting on Friday and should keep dry
weather through at least all of next weekend. Temperatures will
warm back into the 60s and 70s.
.AVIATION...as of 4:54 PM PDT Sunday...For 00z tafs. Weak front
is entering the North Bay at this time with light rain at ksts.
Boundary will pass through the Bay Area this evening with some
light rain and lowering cigs. Southerly winds ahead of the front
will transition to WNW most terminals by 06z except later for the
Monterey Bay terminals as the front will take longer to arrive
down there. Expect vfr conditions Monday but a breezy nw wind
pattern for most terminals by Monday afternoon.
Vicinity of KSFO...Southeast winds for a few more hours this
evening ahead of front with some light rain by about 02z. Precip
will be showery and fast moving with winds turning westerly by
06z. Expect vfr skies by 16z Monday with breezy nw winds.
SFO Bridge Approach...Similar to ksfo.
Monterey Bay Terminals...Expect vfr conditions early this evening
with frontal light rains arriving after 03z. Breezy nw winds on
Monday should mix out morning low clouds and leave vfr skies for
much of the day.
.MARINE...as of 3:00 PM PDT Sunday...Light southerly winds will
veer to the northwest this evening as a front moves across the
coastal waters. Light northwesterly winds will prevail tonight
then increase monday afternoon as high pressure builds in over the
eastern pacific and a thermal trough develops over the state. A
short period westerly swell is forecast to impact the region
beginning monday afternoon and is expected to continue building
through monday night. Choppy squared seas are forecast to persist
through midweek as moderate to strong northwesterly winds prevail.
PUBLIC FORECAST: Bell
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