Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 232112
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
212 PM PDT Sat Sep 23 2017

.SYNOPSIS...
A low pressure trough over the West will keep it comfortably cool
again today. The trough will weaken next week, allowing surface high
pressure to build over Great Basin, which will turn the winds
offshore over southern California. This will set the stage for
sunny, warmer days, and clear, cool nights through the end of the
month. The drying northeast winds will become gusty at times along
the coastal foothills, especially Monday and Tuesday, increasing
the threat of wildfires.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

A continued unseasonably cool day today across the region,
especially inland of course where temperatures continue to run 10
to 15 degrees below normal. A weak coastal eddy is also helping to
keep scattered clouds across the coastal areas and some clouds
banking against the coastal slopes as well. Do not think the
coastal eddy will be strong enough to spin up a widespread stratus
deck tonight but will need to keep an eye on that.

On Sunday as the upper level trough begins to move out of the
Great Basin, surface high pres will develop over the Great Basin,
helping to develop offshore flow over SoCal. This pattern will
strenghten Monday through Wednesday. Temperatures will moderate
Sunday and Monday and spike above normal through the middle of
next week. Although the offshore pattern is not particularly
strong, it will be long lasting, through the end of the work week,
with a coastal troughy pattern possibly developing by next
weekend.

With the moderate offshore pattern, gusty offshore winds will be
most likely Sunday night and into Monday morning and again Monday
night and into Tuesday morning, possibly repeating on Wednesday.
However the strength of the event doesn`t look to reach advisory
thresholds at this time, except for isolated locations.

&&

.AVIATION...
232130Z...Coast/Valleys/Coastal Slopes...Mostly clear skies and
unrestricted vis prevailing through Sunday...except at the beaches
and along the immediate coastal strip where mainly SCT coastal
stratus will linger at times, but not likely to impact any of the
coastal TAF locations. Gusty offshore winds will develop Sunday
afternoon along the coastal slopes and and through and immediately
below the W facing canyons...with gusts to 40 knots possible in the
most wind prone locations.

Mountains/Deserts...Clear with unrestricted visibility through
Sunday morning.

&&

.MARINE...
No hazardous marine weather is expected through Thursday.

&&

.FIRE WEATHER...
Offshore flow will develop on Sunday, and become gusty below the
coastal slopes, canyons and passes of San Bernardino, Riverside,
and Orange Counties Mon/Tue. The RH will drop considerably, on
Sunday with minimum daytime values down to as low as 10% through
Thursday. In the favored, offshore wind-prone areas, we are still
expecting to see occasional winds of 25 to 35 mph with isolated
gusts to 40 mph, especially Mon/Tue mornings. Several hours of
near critical fire weather conditions are possible in these
foothills areas, mainly north of San Diego County Mon/Tue due to
low RH and winds exceeding 25 mph. However, with the limited
coverage and duration of critical conditions, no fire weather
product issuance is anticipated at this time. A significant
concern for the fire weather forecast is the longevity of the hot
and dry weather pattern for much of the work week. The medium
range models do suggest some improvement by next weekend as a
trough may develop along the west coast.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
 encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC/FIRE WEATHER...Brotherton
AVIATION/MARINE...JMB


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