Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 292206
Area Forecast Discussion
National Weather Service San Francisco Bay Area
306 PM PDT THU SEP 29 2016
...LIGHT RAIN RETURNS FOR NORTHERN PARTS OF OUR AREA STARTING ON
.SYNOPSIS...A cooling trend will continue through the weekend as
the marine layer and onshore flow become better established with a
trough deepening along the West Coast. In addition, a dry cold
front will move through on Friday leading to breezy conditions. A
system will drop down from the north over the weekend which will
bring rain to our area especially over the North Bay.
.DISCUSSION...as of 1:38 PM PDT Thursday...Satellite imagery
shows most of the low cloudiness has cleared to the coast.
Exceptions include most of San Francisco, Point Reyes, and much of
the Monterey Bay area. Afternoon temperatures are running much
cooler than those yesterday at this time with many readings in the
60s and 70s, with some areas as many as 16 degrees cooler than 24
hours ago. Locations right along the immediate coast are
struggling to hit 60 degrees, while even the warmest, well-inland
locations have only warmed into the 80s.
The cooling trend will continue Friday and into the weekend as an
upper level trough approaches the coast. A dry cold front will
move across the district on Friday resulting in an increase in
wind speeds, mainly over the coastal waters and areas near the
coast as well as in the near-coastal hills. Wind speeds of 15 to
25 mph with some higher gusts are possible in these areas during
the afternoon and evening.
On Sunday, the main upper trough will move through bringing rain
chances to mainly the North Bay but some showers could occur from
around Monterey Bay northward. The proximity of the upper low will
also give the possibility of thunderstorms with these showers
late on Sunday. Rainfall estimates of around 0.20" in the North
Bay still look reasonable, with around a tenth of an inch across
much of the San Francisco Bay. A few post-frontal showers are
expected to linger into Monday.
A flat ridge will rebuild over the west into the middle of next
week and possible longer bringing a slight warming trend to the
area. The 12Z run of the ECMWF brings another round of showers to
the district possibly by next Sunday. Low confidence in that at
.AVIATION...As of 10:55 AM PDT Thursday...Marine stratus pushed
inland in what looks like mid stratus season. Inland intrusion
still prevalent throughout portions of the North Bay, the Golden
Gate Gap, and Monterey Bay but is showing signs of pulling back
from all inland directions. Wind field may advect additional
clouds into coastal North Bay/coastal San Mateo/around the
Monterey Bay through the late morning and posbl into the early
afternoon. As such, VFR conds expected at sites by 19Z, except
along the immediate coast. Winds increase tomorrow.
Vicinity of KSFO... VFR. Sust onshore winds 15-20kt through the
afternoon. Low confidence on return timing this evening with posbl
04-08Z timing. Winds increase further tomorrow.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Lingering stratus will bring intermittent
IFR cigs to KMRY/KSNS through the late morning. Early return of
stratus by 02-03Z today. LIFR-IFR cigs tonight.
.FIRE WEATHER...As of 3 PM PDT Thursday...The main weather
message will be cooler and wetter conditions heading into the
weekend. The marine layer will deepen as a trough approaches the
region tonight. The biggest fire weather concern the next few days
will be a passing dry cold front Friday afternoon/evening. The
front will be gusty northwest winds 10 to 20 mph with gusts to 30
mph. Despite the cooler/wetter conditions history shows this could
be of concern given the current state of the fuels. Winds will be
peak Friday night and Saturday. Next item of concern will be
precip...including thunderstorm chances. Loma Fire appears more
likely to receive some light precip where the Soberanes will be on
the edge. Instability increases Sunday afternoon over the North
Bay then spreading south. Slight chc of thunderstorms will be
poss. LAL of 2.
.MARINE...as of 10:53 AM PDT Thursday...Weakening pressure
gradient today will bring generally light winds to the coastal
waters today. Winds beginning increase early friday for the north
coast and strengthen through the day. The strongest winds will be
located along the sonoma coast north of pt reyes and along the big
sur coastline by tomorrow afternoon. Strong winds will persist
along the Big Sur coast... especially around Point Sur through
Saturday. Winds decrease sunday morning. Small mixed swell with a
long period southerly swell through the period.
.Tngt...SCA...SF Bay until 9 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 PM
SCA...Pt Arena to Pt Reyes 0-10 nm
PUBLIC FORECAST: Sims
FIRE WEATHER: MM
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