FXUS66 KMTR 162100

Area Forecast Discussion
National Weather Service San Francisco Bay Area
200 PM PDT Mon Oct 16 2017

.SYNOPSIS...Look for another warm day regionwide today. A gradual
cooling trend is forecast for Tuesday and Wednesday. The pattern
will then change as a system drops down from the north and brings
generally light rainfall to parts of the area late Thursday into


.DISCUSSION...as of 2:00 PM PDT Monday...Another warm day is in
store for much of the San Francisco Bay Area and central
California coast. Temperatures as this early afternoon have
already warmed to the upper 80s and low 90s for parts of the Santa
Cruz Mountains near Scotts Valley. Expect these warm-to-hot
temperatures to also be realized in the North Bay where wildfires
continue to burn. Sonoma and Napa Counties are forecast to warm to
the middle to upper 80s with a few isolated locations surpassing
90 degrees. South Bay and the Salinas Valley will also be
unseasonably warm with temperatures in the upper 80s to low 90s.
Additionally, the lack of substantial onshore flow will allow
coastal areas to warm to the 80s along the Monterey Bay shoreline.
The 2 pm PDT in our backyard adjacent to the Monterey Airport was
84 degrees.

The upper level ridge that is responsible for these unseasonably
warm-to-hot conditions will shift south and weaken over the next
24 hours as a trough begins to develop in the Gulf of Alaska. This
will mark the beginning of significant cooling trend through the
middle of the week with increasing chances of precipitation for
parts of the area later in the week. From Monday to Tuesday,
temperatures will generally cool by about 5 to 10 degree across
inland communities with coastal areas cooling by 8 to 15 degrees.
The cool down will continue into Wednesday as highs will range
from the 60s along the coast, low 70s to near 80 in the North and
East Bays, and middle 70s to low 80s for Interior Monterey County
and San Benito County. On Thursday warmest temperatures in the
area will struggle to get much above 70 as a longwave through
approaches the West Coast from the northern Pacific.

At this point, the best chance for rain in the area will occur
late Thursday for coastal Sonoma County and extending southward
after sunset and overnight. There still remains uncertainty as to
how far south the precipitation will go. Latest model guidance has
backed off on precipitation amounts, especially for Monterey and
San Benito Counties. Current forecast calls for about 0.15 to 0.30
inches for the North Bay when all is set and done by Friday
morning, and about 0.05 to 0.15 for San Francisco and East Bay.
Motorists should be prepared for the potential for wet/slick
roadways on Friday morning.

Temperatures are then forecast to rebound Saturday and beyond as
another ridge builds over the Southwestern United States. Models
suggest the return of widespread 80s for much of the North, East,
and South Bays, with parts of the Salinas Valley reaching the 90s.
This is consistent with the Climate Prediction Center's 6 to 10
day outlook (valid October 22 to 26) which advertises increased
likelihood of above normal temperatures and below normal


.AVIATION...as of 10:38 AM PDT Monday...For 18z Tafs. Smoke/haze
will continue to affect North Bay terminals, and may also affect
VIS for SF Bay terminals through the day. Otherwise, VFR will
prevail through the forecast period, as high clouds filter in and
out of the area. Weak onshore winds this afternoon, generally
around 10 kt, decreasing by sunset.

High confidence.

Vicinity of KSFO...VFR with periods of haze possible that may drop
VIS below 6SM at times. Light winds becoming becoming W/NW around
10 knots by early afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR through the forecast period. E/SE
winds will likely continue for KSNS through about 21z before the
sea breeze kicks in. Generally light onshore winds this afternoon
and evening.


.FIRE WEATHER...As of 3:30 AM PDT Monday...Fairly light winds can
expected today across our entire region along with warmer than
normal temperatures. High pressure will weaken starting on Tuesday
which will lead to cooler temperatures plus a return of onshore
flow. This will lead to an improvement in humidity values
especially by Wednesday. For Thursday into Friday wetting rain is
likely for part of our region as a system drops in from the Gulf
of Alaska. Winds will be breezy as it moves across, however the
combination of higher humidity readings and cooler temperatures
should help to keep the fire weather risk relatively low.


.MARINE...as of 01:57 PM PDT Monday...High pressure over the
eastern Pacific will gradually weaken and move southward this
week. A cold front from the Gulf of Alaska will arrive in the
California coastal waters later Thursday along with rain spreading
southeastward across the waters and bays. Moderate to long period
southwesterly swell may temporarily arrive Tuesday mixing in with
northwesterly swell. A very large northwesterly swell train, the
largest of this season so far, is then forecast to arrive Thursday
night through Friday.





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