Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 250426
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
926 PM PDT Sun Sep 24 2017

.UPDATE...
At 9 PM PDT, a 1022 mb surface high over central UT and a 1011 mb
surface low just off the coast of San Diego was creating weak
northeast to easterly winds along coastal mountain slopes. Water
vapor imagery showed an upper-level trough to our east, and an
upper-level ridge well off the coast, with NNW flow aloft over SW
CA. With the exception of some high clouds moving in, skies will
be clear of low clouds overnight. No changes to the forecast
needed this evening.

&&

.SYNOPSIS...
High pressure over the Great Basin will force weak to moderate
offshore flow over Southern California for most of the week. The
dry northeast winds will lower humidity, and bring much warmer
days and continued cool nights. Winds will be gusty at times along
the coastal foothills, and will increase the threat of fire
behavior, especially from now through the middle of the week.

&&

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

.PREV DISCUSSION...
Offshore winds have kicked in today for locations along and west
of the coastal slopes. Winds have not been particularly strong but
the VWPs have been showing some isolated 25 knot measurements
just off the deck. These winds are bringing very dry and much
warmer conditions to the valleys with temperatures about 10
degrees above yesterdays readings, and dewpoints as much as 20 to
30 degrees lower. With the offshore flow as expected skies are
completely clear.

The offshore winds will increase tonight into Monday morning with
diurnal drainage and will pick up through the canyons and along
the coastal slopes, however we are not expecting these winds to
reach advisory levels except in isolated and remote locations as
is common during a moderate offshore regime. The pattern will
continue through Wednesday and then we will see some relaxing in
the offshore gradients due to a brief cutoff low developing in the
bottom of the trough over SE CA and W AZ with some marine layer
and sea breeze action each day over the coastal strip and into the
western valleys.

By next weekend, a broad high pres ridge may settle over SoCal
bringing another warmup with temperatures several degrees above
normal for all areas and no rain in site.

&&

.AVIATION...
250330Z...Offshore flow will bring clear skies and unrestricted
visibility through Monday. Strongest winds should be felt
below/through the passes and canyons, especially in the northern
Inland Empire south of the Cajon Pass. Areas of LLWS between 500-
2500 ft AGL will accompany the gusty winds in the northern Inland
Empire, Coachella Valley and Orange County. Minimal impact from
the winds is expected at the TAF sites, though KONT, KSBD, KSNA
and KPSP may see peak gusts of 20-25 kt out of the northeast with
LLWS possible through 17Z Monday.

&&

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

&&

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

&&

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

$$

UPDATE...JJT
PUBLIC...Brotherton
AVIATION/MARINE...Albright



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