Area Forecast Discussion
Issued by NWS San Diego, CA

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945
FXUS66 KSGX 120029
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
124 PM PST Mon Dec 11 2017

.SYNOPSIS...
High pressure aloft and weak offshore flow at the surface will
likely keep the weather warm and dry through at least this
weekend. Locally gusty northeast to east winds will occur in the
coastal foothills, slopes and in the passes and canyons. Skies
should be mostly clear except for passing high clouds at times.

&&

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

Afternoon visible satellite shows scattered high clouds
(associated with an upper low over Baja) continuing to stream into
the region. The 12Z sounding from Miramar continues to show a
very dry profile up through 500 mb and then the high level
moisture shows up above that level. The sounding also shows weaker
easterly winds in the low to mid levels of the atmosphere, at
only around 5-10 kt. This lack of upper level support and some
weakening in the offshore pressure gradients (down to 5.9 mb from
San Diego to Las Vegas whereas it was 8.9 mb at this time
yesterday) has resulted in much weaker Santa Ana winds this
afternoon. Winds continued to back off today, as the 1 pm
observations show northeast to east wind gusts of 15-25 mph and
locally 35 mph in the coastal foothills/slopes and passes/canyons
while there were westerly sea breezes of around 10-15 mph in the
coast and valleys.

Water vapor satellite shows an upper level ridge over the Great
Basin and the aforementioned upper level low over Baja. Offshore
flow will continue through Thursday but remain weak, with
strongest winds of 10-20 mph with 30-35 mph gusts and locally up
to 45 mph in the coastal foothills/slopes and passes/canyons
through Wednesday and even lighter Thursday. The weak offshore
flow and dry atmosphere will continue to bring warmer than normal
weather (highs mostly 5-15 degrees above normal) to the region
today through much of the week, and possibly into the weekend and
early next week as well, with models not indicating any
significant trough moving down into Southern California. Thus,
rain or cooler weather is not expected through early next week.
There really isn`t even a hint of the marine layer coming back to
the coast except for possibly Friday when there may be a brief
return of onshore flow as the upper level ridge gets pushed west
and a trough moves down through the Inter-mountain West. However,
models show the offshore flow returning on Saturday and
continuing possibly into next Monday.

&&

.AVIATION...
112130Z...SCT-BKN clouds AOA FL200 and unrestricted vis through
Tuesday afternoon.

&&

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

&&

.FIRE WEATHER...
Although the offshore/Santa Ana winds will be much weaker today
through at least Thursday, day-time humidity for everywhere
except coastal areas will be very low (down to 5-10 percent each
day) with very poor overnight humidity recovery. Strongest winds
will be in the coastal foothills/slopes and passes/canyons where
winds of NE to E winds 10-20 mph with gusts to 30-35 mph and
locally 45 mph can be expected through Wednesday. Elsewhere, wind
gusts will mainly be 15 mph or less. Red Flag Warnings not
anticipated as winds will be too weak, with strongest winds pretty
localized. However, elevated fire weather conditions will
continue.

&&

.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...Harrison
AVIATION/MARINE...JJT



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