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Area Forecast Discussion
FXUS66 KSGX 170950
Area Forecast Discussion
National Weather Service San Diego CA
250 AM PDT Fri Sep 17 2021
Fair and seasonal weather is expected this coming week. Coastal
clouds will continue nights and mornings. High pressure building
early next week will bring warmer weather Monday through Wednesday.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Coastal clouds were slowly expanding in coverage early this
morning and should cover most of the coastal basin by sunrise. A
weak upper low off the SoCal coast will draw up subtropical
moisture and clouds across the southeast corner of the state
(we're seeing that already). Skies will be mostly sunny west of
the mountains today after coastal clouds clear, but cumulus and
other mid-level clouds will accent the sky today and tonight in
the mountains and deserts. Thunderstorms are possible east of our
area in Imperial County and eastern parts of Riverside and San
Bernardino Counties. Temperatures will continue a little below
normal for this time of year. The upper low fills and moves
northeast Saturday and Sunday. So the weekend will be just like
today, minus the higher clouds. A progressive and rather deep
trough of low pressure will move through the northwestern U.S.
Sunday and Monday. For SoCal this will probably generate a
coastal eddy Sunday night and Monday, but the marine layer cloud
coverage won't change too much each night and morning. The colder
air moving into the Great Basin will produce offshore flow and
weak offshore breezes Monday night and Tuesday morning. Highest
gusts might be 25-30 mph, and it won't be very hot or extremely
dry. Recent guidance has been consistent in this weak offshore
flow solution and has tempered concerns about getting a full blown
Santa Ana event. The higher pressure aloft and the touch of
offshore flow will start a warming trend Monday that peaks
Wednesday, the last day of summer (or first day of fall?). High
pressure seems to weaken again later next week for a modest
cooling trend. The marine layer and coastal clouds won't go away,
but will retreat as weak offshore flow, subsidence and plenty of
sunshine push temperatures above normal. On Wednesday, the
projected warmest day, 90s will be common in the Inland Empire and
high desert, with upper 80s in the western valleys and around 105
in the lower desert. Forecaster brains are turning the page to
fall thinking as the season changes right on schedule.
170900Z...Coast/Valleys...Low clouds with bases 1500-2000 feet MSL
will continue for coastal and valley areas inc KONT. Visibility of 3
SM in BR/HZ possible near higher coastal terrain and along the
inland extent of the stratus in the valleys. Scatter out expected 16-
Mountains/Deserts...Clear skies with unrestricted vis through
No hazardous marine weather is expected through Wednesday.
Fire weather conditions will continue elevated to locally critical
for a few hours along the desert slopes and near passes during
afternoons and evenings this weekend. Slightly higher humidity is
expected today. Warmer and drier weather is expected Monday
through Wednesday with higher pressure and weak offshore flow, but
conditions do not appear to be critical.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.