Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 240004
Area Forecast Discussion
National Weather Service San Francisco Bay Area
504 PM PDT Thu Mar 23 2017
...Rain and gusty southerly winds return on Friday...
.SYNOPSIS...Rain and moderately south winds return to the North
Bay area late tonight as a frontal system approaches. Rain and
winds will spread southward Friday as the front moves across the
region. A break in the rain is expected Saturday with showers
anticipated to return Sunday night into Monday as a low pressure
system moves through the region.
.DISCUSSION...as of 1:40 PM PDT Thursday...After an active
weather day yesterday, today -- as expected -- has been tranquil
with just scattered clouds. Temperatures have been running close
to values from Tuesday with most spots in the upper 50s to the
lower 60s. Hard to believe in less than 24 hours we will be
dealing with another round of active weather.
Synoptically a cold front associated with a 988 MB low heading
toward British Columbia will move through our region on Friday.
Models have shown very little variation from previous runs, so the
forecast was changed very little during the shift. Rain will move
north-to-south starting overnight in the North Bay then down to
the SF Bay Area early in the morning and to Monterey Bay Region
close to noon. Rain rates will pick up with the approaching front
and could be moderate to heavy at times. Current timing brings the
main band through SF Bay late in the morning or early in the
afternoon. In fact, if the current NAM verifies the bulk of the
rain will fall after morning rush and before the afternoon
commute. Along with the rain southerly winds will increase with
many spots forecast to see gusts of 25 to 35 mph. Winds for higher
elevation locations will be stronger -- gusts over 45 mph are
Rainfall totals still look like 1.5" to 3" for the North Bay with
2/3" to 1.5" around SF Bay with generally less than 2/3" for
points to the south. All of the coastal ranges are expected to be
in the 2-4" range with a few local spots possibly seeing slightly
Rain will switch to showers behind the front with light
precipitation possible through Friday night. However, by mid-day
Saturday all of the rain should be well to our south and east.
Similar to today`s time period, that break will be short as
another system moves across on Sunday. This one should be quite a
bit weaker and will have less moisture to utilize. In general
amounts will be around half of what we get out of the first round.
Rain will switch over to showers going into Monday.
A ridge of high pressure will build back to our region starting
next Tuesday, although a system will dive down from the north late
Wednesday/early Thursday possibly bringing a few light showers.
However, after it departs a more pronounced pattern change will
take place as a stronger ridge of high pressure returns to our
region. This should give us dry conditions with warmer
temperatures toward the end of next week possibly through the
.AVIATION...As of 4:55 PM PDT Thursday...For 00z TAFs. VFR
conditions expected to prevail through the evening hours with
westerly winds at 10-15 kt. Showers expected to move in from North
to South beginning with KSTS around 04z Friday. Steady rain
expected across all terminals by tomorrow morning. MVFR ceilings
possible early Friday morning for Bay Area terminals. Low
confidence on timing of the rain.
Winds are expected become southerly on Friday with possible gusts
exceeding 20 to 25 kt by 18Z. High confidence on wind direction,
low confidence on the timing and gust magnitude.
Vicinity of KSFO...VFR this evening and overnight transitioning to
MVFR ceilings and rain by Friday morning. West winds 10-15 kt this
evening becoming southerly by 6 to 8Z with gusts exceeding 20 kt
possible by 15 to 18Z.
SFO Bridge Approach...Same as KSFO.
Monterey Bay Terminals...VFR this evening and overnight with
generally light winds and occasional gusts at KSNS before sunset.
Rain showers are expected to begin impacting after 12 to 16Z.
.MARINE...as of 04:42 PM PDT Thursday...A storm system is
currently approaching the waters from the west. This will cause
winds to increase and turn southerly late this afternoon.
occasional gale force gusts are possible late tonight and into
tomorrow...especially for the northern coastal waters. Rough seas
possible just ahead of and behind the frontal passage, but should
begin to decrease by Saturday. Expect northwest winds to return
by Saturday as well before briefly becoming southerly on Sunday
as another weak system moves over the waters.
.Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 5 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 5 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm from 9 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 9 PM
SCA...Pt Arena to Pt Reyes 0-10 nm from 8 PM
SCA...SF Bay from 5 AM
PUBLIC FORECAST: Bell
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