Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 201802
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1000 AM PST Mon Nov 20 2017

.SYNOPSIS...
High pressure aloft along the West Coast will bring unseasonably
warm weather this week and mostly clear skies. High temperatures
will be 15 to 25 degrees above average Wednesday and Thanksgiving. A
slow cooling trend will begin Friday and continue through next
weekend, but temperatures will remain above average.

&&

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

High clouds were drifting over the region with a few patches of fog
over the coastal waters. Marine inversion was surface based on the
NKX sounding this morning and very weak and nearly surface based in
the AMDAR soundings, so any stratus/fog that occurs today will be
restricted to the coastal waters and beaches as there is only a +1
MB MSLP gradient from San Diego to the lower deserts, which is
actually a little stronger versus 24 hours ago. Highs in the lower
80s in some of the valleys and lower deserts for today looks good.

Upper level high will build from off the west coast of Baja north
into southern California/Arizona through Wednesday, continuing
Thursday, then gradually shift east Friday through the weekend. Weak
offshore flow will prevail at the surface. Local WRF has a gradual
lowering of near-surface RH over the coastal waters through tonight,
so the chance of any fog at the coast will be very low
tonight/Tuesday. The profile gets quite warm Tuesday through
Thursday, with 850 MB temps reaching 22-23 deg C in some areas west
of the mountains Wednesday, which is near the late-November record
of 22.7 deg C for NKX. Hence, we will likely not only have record
highs Tue-Thu but we could approach highest temps for this late in
the year. However, with low sun angles and low humidity, the heat
will be more bearable, especially in wind-sheltered areas which will
still have cool nights with lows in the 40s and 50s. Moderate
offshore flow will bring locally gusty northeast winds to the
southwest of mountain crests and through and below passes/canyons,
but with limited support aloft, most gusts will be 40 MPH or less.

A trough in the northeast Pac will gradually shift east during the
weekend and bring a cooling trend Friday through the weekend.
However, temps will remain above average. There could be a period of
dense fog in coastal areas when the marine layer returns, though
timing is far from certain as this probably will not be until at
least Saturday. No precipitation is expected through the weekend,
with only a small chance early next week when the trough moves
through northern California.

&&

.AVIATION...
201600Z...P6SM vis and SCT-BKN clouds AOA 20000 ft msl expected to
continue for all areas through Tuesday morning, with only a very
small chance for dense fog developing within 3 sm of the coast
during the 21/0300-1500 UTC time-frame.

&&

.MARINE...
Small chance of patchy dense fog developing over the coastal waters
late tonight into Tuesday morning. Otherwise, No hazardous marine
conditions are expected through Friday.

&&

.FIRE WEATHER...
Locally elevated fire weather conditions area expected along the
coastal slopes in San Diego County and below the passes and
canyons in Riverside and San Bernardino Counties on Wednesday and
Thursday. Conditions shouldn`t be extreme, but relative humidity
values of 10-15% and wind gusts of 25-40 mph will bring elevated
fire weather conditions.



&&

.SKYWARN...
Skywarn activation will not be needed this week.


&&

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

$$

PUBLIC/FIRE WEATHER...Maxwell
AVIATION/MARINE...Harrison


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