National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2017-10-10 00:18 UTC


658 
FXUS66 KMTR 100018
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
518 PM PDT Mon Oct 9 2017

.SYNOPSIS...Wind speeds will continue to diminish through the day 
and turn onshore near the coast. However, warm and dry weather 
conditions will prevail through the remainder of the day. A cooling 
trend will take place on Tuesday with temperatures falling below 
seasonal averages by late week. Breezy northerly winds will also 
likely develop in wake of a weak frontal passage Wednesday. 

&&

.DISCUSSION...as of 01:50 PM PDT Monday...Seasonably mild and 
very dry weather conditions prevail over the region this 
afternoon. With this, the wildfires that started overnight across 
the North Bay continue to burn with little to no containment based
off of information from Cal Fire. Winds across the region have 
been diminishing through the early afternoon as forecast, which 
should provide some relief to fire fighting efforts. Elsewhere, a 
patch of stratus has been moving northward from off of the Big Sur
Coast through the day and now is pushing into the northern 
portions of the Monterey Bay, such as Santa Cruz where 
temperatures have dropped by several degrees. 

A slight cooling trend is forecast on Tuesday as the short-wave 
ridge over the region shifts inland ahead of a deepening mid/upper 
level trough. With this, may see a slight increase in the marine 
influence and coastal stratus both tonight into Tuesday morning and 
again Tuesday night into Wednesday morning. Additional cooling is 
forecast on Wednesday as a frontal boundary pushes through the 
region along with cold air advection aloft. By Wednesday afternoon, 
temperatures look to be around 10 degrees cooler than those today. 
With a broad mid/upper level trough forecast to linger over the West 
Coast through late week, conditions will be seasonably cool with 
daytime temperatures only warming into the low/mid 60s coast to 
lower 70s inland. Breezy northerly winds will also develop once 
again in wake of the frontal passage and persist into late week. 
Overnight temperatures will also be cool late in the week, generally 
in the 40s to lower 50s around the San Francisco Bay. By Thursday 
morning and again Friday morning we cannot rule out patchy frost in 
some of the wind sheltered inland valleys as well.

May see a slight warming trend as we head into next weekend as the 
broad mid/upper level trough shifts inland once again. This should 
allow temperatures to warm back to near seasonal averages along with 
continued dry weather conditions. 

&&

.AVIATION...as of 5:18 PM PDT Monday...Smoke due to fires in the 
North Bay continues to reduce visibilities to IFR over the North
Bay, smoky and hazy conditions have swept as far southwest as the
Farallon Islands with a recent report of 7 miles visibility. Elsewhere
weak onshore winds and clear skies have helped keep VFR going at the
terminals. Not indicated in 00z tafs, but caveat here is that little
change in air mass stability is forecast tonight may trap more smoke
and haze overnight degrading slant-wise and horizontal visibilities
over more of the Bay Area into Tuesday morning.

Visible imagery shows an area of stratus and fog moving rapidly north
along the coast reminiscent of a southerly surge, however a nearly
flat SMX-SFO gradient does not support a typical wind reversal. As
best as can tell from obs and model forecasts this is part of a 
surface to low level eddy circulation spun up from the recently 
strong to very strong N-NE Bay Area winds; not a lot of confidence
in wind direction forecasts in the models for tonight, but for 
what it's worth the NAM is not forecasting a southerly pressure 
gradient. Best guess is that this circulation will continue to 
spin down with general onshore flow prevailing at the terminals 
overnight. Marine inversions are quite compressed, down to a few 
hundred feet, thus any stratus and/or fog should stay confined to 
the immediate coastline tonight and Tuesday.

Vicinity of KSFO...VFR. Recent wind shift to SW per observations will
probably stick for the evening, low confidence forecast. Otherwise
in general expecting W wind flow near 10 knots tonight and Tuesday.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Low to moderate confidence VFR. Light onshore
winds becoming E-SE overnight should help keep VFR going tonight. Onshore
winds redevelop Tuesday afternoon and evening.

&&

.FIRE WEATHER...As of 3:20 AM PDT Monday...A Red Flag Warning 
remains in effect for the North and East Bay Hills and Valleys and
the Santa Cruz Mountains until 5 am Tuesday morning. Strong and 
dry offshore winds were occurring in the hills of the San 
Francisco Bay Area early Monday morning, particularly in the North
Bay where these strong winds were fanning multiple wild fires. 
Locally gusty winds were also occurring near sea level, primarily 
in the North and East Bay. Strong and gusty winds are expected to 
persist through at least sunrise, and then gradually diminish 
through midday. Although winds are expected to decrease 
significantly by late today, the Red Flag Warning will likely 
remain in effect into tonight due to continued warm and very dry 
conditions and because of the multiple wild fires across the North
Bay. 

&&

.MARINE...as of 4:42 PM PDT Monday...Fairly light winds can be 
expected to continue through tonight. Northwesterly winds will 
increase again Tuesday afternoon over the northern outer waters, 
and moderate northwesterly winds will then increase across all of 
our coastal waters through midweek.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...NONE.

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Canepa
MARINE: Bell 
FIRE WEATHER: Dykema

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