Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 262055
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
155 PM PDT Tue Sep 26 2017

.SYNOPSIS...
High pressure over the Great Basin will continue to bring
offshore flow through Wednesday with sunny, warm days and cool
nights. Localized gusty winds will occur on the coastal sides
of the passes. It will get slightly warmer Thursday and Friday
with lighter winds. Conditions will cool slightly this weekend as
a trough moves by to the north.

&&

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

High pressure over the Great Basin continues offshore pressure
gradients across Southern California. However, the gradients are
weakening. Peak wind gusts this morning were only at 34 mph and
with the gradient decreasing a tad, expect peak gusts tonight-Wed
morning only to be at 20-30 mph. Low relative humidity continues
with only teens most areas beyond about 20 miles of the coast. A
sea breeze is pushing inland this afternoon, moderating humidity
from west to east as it pushes by.

WRF shows a little eddy developing and sending low cloud and fog
potential to the coast. However, this was way too aggressive last
night and we believe it is just as aggressive tonight. Still,
there is a chance of some low clouds and/or fog developing along
the coast, mainly along the San Diego coast. Low confidence on
this occurrence.

Weak offshore flow prevails through Friday as the longwave
trough, which has been over the West since last week, finally
lifts out. That keeps inland areas quite dry and warm through
Friday with daytime temperatures several degrees above average.

Global models show another trough moving by mainly to the north
this weekend. This will create onshore flow and a slight cooling
of temperatures as it does so.

&&

.AVIATION...
262030Z...Mostly clear skies through Wednesday. Locally breezy
northeast winds will produce intermittent and isolated up/downdrafts
LLWS in the foothills of the Santa Ana Mountains and south of the
Cajon Pass again Wed between 09Z and 21Z. KONT and KSBD may be
impacted at times.

Cigs blo 1000 ft Msl and vis blo 3SM could return to the southern
coastal areas of San Diego County after 09Z Wed, but confidence is
low.

&&

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

&&

.FIRE WEATHER...
Minimum relative humidities over the Inland Empire and the far
inland valleys will be in the teens through the remainder of the
day. However, as winds continue to relax, critical fire
conditions are not anticipated. A sea breeze is moving inland and
will continue to do so with RH moderation from west to east
through this evening.

RH is forecast to increase Wednesday through Friday over coastal and
western valley areas, but minimum RH will still fall to 15-25
percent across the far inland valleys. Overnight recovery will be
better, and northeast winds will be weaker as well during this time.
A general onshore flow pattern will return this weekend for cooler
conditions and higher daytime humidity.

&&

.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...Gregoria
AVIATION/MARINE...PG


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