Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 202155
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
200 PM PST Mon Nov 20 2017

.SYNOPSIS...
High pressure aloft along the West Coast will bring unseasonably
warm weather this week and mostly clear skies except for periodic
high clouds. High temperatures will be 15 to 25 degrees above
average Wednesday and Thanksgiving. A slow cooling trend will begin
Friday and continue through early next week, 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, and the patches of fog
over the coastal waters dissipated late this morning. Warmest areas
had temperatures in the upper 70s to lower 80s, mainly in the
valleys west of the mountains. Except for the high clouds, skies
should be clear tonight, especially with HRRR solutions showing few
to no low clouds in the coastal waters versus earlier solutions
which had some.

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...
202055Z...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 Saturday.

&&

.FIRE WEATHER...
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 Wednesday and Thursday.
Conditions shouldn`t be extreme, but relative humidity values of 10-
15% and wind gusts of 25-40 mph will bring the 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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