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Forecast Discussion for San Diego, CA

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FXUS66 KSGX 270403

Area Forecast Discussion
National Weather Service San Diego CA
903 PM PDT Sat Sep 26 2020

High pressure will slowly build over the West early this coming
week, bringing much warmer weather and offshore flow. Gusty east to
northeast winds will spill through the passes and down the coastal
slopes by Monday, driving the marine layer offshore, and increasing
the wildfire danger. Winds will weaken through midweek, but very dry
and warm conditions will continue through the work week. Cooler
weather, and the marine layer, return by next weekend.



Marine clouds were already thick along parts of the San Diego County
Coast and offshore at 8 PM PDT. The sfc pressure gradients were
weak, but westerly winds were still gusting 25-30 MPH through the
passes and into the deserts. The 00Z Miramar sounding had a 6.5C
inversion based near 1800 FT MSL. Slight warming was observed above
the inversion, but winds were light and variable all the way up
through 10K FT. Some of that slight warming will be felt inland on
Sunday, but little change is forecast over coastal areas. No
forecast changes this evening.

From previous discussion...

Enjoy the seasonal weather while it lasts, because a heat wave is
in store Sunday through much of next week. High pressure will
begin to build over the West on Sunday, bringing hot weather to
the region for much of the week. The heat will be more noticeable
on Monday, and will peak Tuesday through Thursday. The greatest
warming will be in the inland valleys and along the coast. The
inland valleys will be well into the upper 90s, with some spots
reaching over 100 degrees Tuesday through Thursday. Coastal areas
will also be feeling some heat too, with mid to upper 80s likely,
perhaps some inland coastal areas reaching into the 90s.

Pressure gradients will shift offshore Sunday through Tuesday,
bringing breezy northeast to east winds to the mountains, passes,
and foothills of the valleys. Winds will mostly be weak on
Sunday, with peak gusts around 25 to 30 mph. The strongest winds
are looking to be late Sunday night into Monday afternoon, with
gusts generally peaking at 35 to 40 mph. Higher gusts may occur in
the windier canyons and passes. Winds will decrease Monday
evening, and could increase again on Tuesday, but current model
guidance suggests these winds will be weaker than on Monday. This
offshore flow will also bring low humidity to the mountains,
passes and foothills, with minimum daytime humidity of 10 to 15
percent. Winds, combined with low humidity, will elevate the fire
weather threat through much of the week, with critical fire
weather conditions expected for Monday. A Fire Weather Watch
remains in effect for Monday for the Riverside and San Diego
mountains, as well as the foothills and through the San Gorgonio
Pass. The San Bernardino Mountains were included into the Fire
Weather Watch in this forecast package.

We may see a very slight reprieve from the heat sometime late
next week or next weekend, but temperatures still look to remain
warm and above normal through at least next weekend.


270245Z...Coast/Valleys...CIGS with bases 1000-1400 ft MSL and tops
to 1800 ft MSL will spread around 25 mi inland between 04Z and 09Z.
Vis restrictions, generally 2-4 SM, will be confined to elevated
coastal terrain and some valleys. CIGS at KONT will be unlikely, but
some brief vis 5-6 SM in HZ may occur 11-15Z. Clouds will clear
toward coast 17-19Z, and may be somewhat slow to clear near beaches
and at coastal terminals. CIGS with bases 800-1200 ft MSL will
return starting near 02Z Mon.

Mountains/Deserts...VFR conditions through the period.
East/Northeast SFC winds 15-20 kts with gusts to 30 kts will develop
near and west of mtn ridges and through passes Sun night, mostly
after midnight. Areas of LLWS and MOD up/dwn drfts will be possible
beginning Sun evening.


Northwest winds may see gusts approach 20 kts over the Outer Waters
Tuesday afternoon and evening. Otherwise, no hazardous marine
conditions are expected through Thursday night.


The marine layer will extend into the western valleys again tonight.
The marine air will maintain higher humidity in these areas through
the weekend.

On Sunday, weak offshore winds will begin to surface in the
mountains. Northeast to east winds of 10 to 20 MPH  will occur,
along with minimum RH of around 15 percent. This will bring elevated
fire weather conditions on Sunday far inland.

The stronger offshore winds will arrive Sunday night and Monday with
northeast to east winds of 15 to 25 MPH gusting to 40 MPH and
minimum RH of 10-15 percent. Critical fire weather conditions are
possible for the mountains, passes and coastal foothill areas with
drier air spreading westward toward the coast. A Fire Weather Watch
is in effect from 5 AM to 5 PM for the Riverside, San Bernardino,
and San Diego County mountains, and valleys.

Weak to occasionally moderate offshore winds, lower RH, and hotter
weather are expected Tuesday and Wednesday, resulting in elevated to
near-critical fire weather conditions through much of next week.


Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


CA...Fire Weather Watch from late Sunday night through Monday
     afternoon for Riverside County Mountains-Including The San
     Jacinto Ranger District Of The San Bernardino National
     Forest-San Bernardino County Mountains-Including The
     Mountain Top And Front Country Ranger Districts Of The San
     Bernardino National Forest-San Bernardino and Riverside
     County Valleys  -The Inland Empire-San Diego County Inland
     Valleys-San Diego County Mountains-Including The Palomar
     And Descanso Ranger Districts of the Cleveland National
     Forest-San Gorgonio Pass Near Banning.





Previous Forecast Discussions may be found at
NWS San Diego, CA (SGX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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