Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 250504
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1004 PM PDT Sun Sep 24 2017

.SYNOPSIS...A gradual warming trend will continue through the first
half of the workweek as high pressure across the eastern Pacific
builds over California. While slightly cooling is expected late in
the week, temperatures are forecast to remain above seasonal
averages.

&&

.DISCUSSION...as of 09:20 PM PDT Sunday...Aside from some high
cloudiness passing through from the north, mostly clear skies
prevail districtwide with the stratus deck having retreated well
offshore. High temperatures this afternoon were generally in the
70s near the water and 80s elsewhere. Downtown San Francisco
itself reached 80 deg, 6 deg warmer than on Saturday and 10 deg
above the climatological normal for the date. Mid-evening
temperatures remain on the mild side, with a few locations still
up in the lower 70s.

Present forecasts appear on-track, though have made some upward
adjustments to the Max Temp grids and forecasts for Monday based
on the actual highs today and latest model output.

.PREV DISCUSSION...As of 01:58 PM PDT Sunday...Sunny conditions
persist over the region this afternoon as the air mass aloft warms
in response to weak offshore flow and building high pressure over
the eastern Pacific. Meanwhile, at the surface, winds along the
coast remain light and slightly onshore while portions of the
interior are experiencing weak north/northeast winds. These
conditions have resulted in a region- wide warming and drying
trend that will continue into the midweek time frame.

Look for temperatures overnight to remain on the cool side of
average for most valley and coastal locations while a more noticeable
warming trend begins in the hills. Temperatures region-wide will
continue on a warming trend Monday and ramp up Tuesday into
Wednesday as surface flow becomes predominantly offshore. By
midweek, 850 MB temperatures are forecast to approach 20 deg C and
will allow for afternoon high temperatures to reach into the
mid/upper 80s at the coast with widespread 90s inland. However, even
the warmest inland areas are likely to stay below 100 degrees and a
more uniform temperature spread in the 80s to mid 90s appears most
likely Tuesday through Thursday.  With this said, the threat for
heat related illnesses will likely remain in the low to moderate
category given decent overnight cooling.

Slight cooling is then forecast by Friday as weak onshore flow
returns to the coast in response to a mid/upper level trough pushing
inland over the Pacific Northwest. However, the ridge of high
pressure does not completely get replaced and temperatures region-
wide will remain at or slightly above seasonal averages. The medium
to longer range forecast models agree that an upper level ridge will
once again become the dominate weather feature across our region by
late next weekend. This will likely lead to another warming trend by
next Sunday into Monday.

&&

.AVIATION...As of 10:04 PM PDT Sunday...Sct-bkn cirrus clouds are still
sweeping in from the north. High confidence VFR forecast tonight through
Monday due to dry offshore wind flow.

Vicinity of KSFO...VFR. Lighter westerly surface wind will shift over
to N-NE much later tonight into early Monday afternoon. Westerly wind
forecast to resume from 22z Monday through Monday evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Light E-SE winds tonight and Monday morning.
Onshore wind returns Monday afternoon and evening.

&&

.FIRE WEATHER...As of 9:00 PM PDT Sunday...The warm and dry air
mass over the area will continue to prevail through at least
Wednesday. Relative humidity values in the hills will continue to
drop into the teens during the afternoon hours with overnight
humidity recoveries no higher than 30 to 35 percent. In addition,
periods of moderate and gusty northeast winds are expected at
times, especially Monday night into Tuesday morning and again
Tuesday night. Each of these will also result in further drying of
the air mass. Red Flag Warnings are in effect for elevations
above 1000 feet in the North Bay and East Bay through Wednesday
afternoon.

&&

.MARINE...as of 8:13 PM PDT Sunday...High pressure over the
eastern Pacific and a thermal trough over the California interior
will keep northwesterly winds going over the coastal waters. The
strongest winds will be over the northern outer waters with
generally lighter winds and seas over the near shore waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

$$

PUBLIC FORECAST: Blier/RGass
AVIATION: Canepa
MARINE: Canepa
FIRE WEATHER: Blier

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