Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 211702
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
945 AM PDT Sat Oct 21 2017

.SYNOPSIS...
A Santa Ana weather pattern will bring hot, dry weather and very low
humidities Sunday through Wednesday. The strongest winds will
surface Monday and Tuesday. The winds will weaken Wednesday with
cooling spreading inland Thursday and Friday.

&&

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

Santa Ana winds started surfacing in the mountains this morning with
peak gusts of 36 mph at Crestline Ridge in San Bernardino County,
and 40 mph at Pleasants Peak in the Santa Ana Mountains. Dewpoints
were 15-25 degrees lower than 24 hours ago in the mountains, and 5-
10 degrees lower in the lower terrain. As of 8 AM the lowest values
were in the San Bernardino Mountains with 12F at both Big Pine and
Green Valley Lake, and 14F at Baldwin Lake.

The forecast is on track this morning and no significant changes are
needed. The pressure gradients were about 8 mb offshore between a
1023 mb surface high over Nevada and 1015 over the SoCal coastal
waters. The northeast winds today and Sunday will be strongest in
the mountains, foothills and into the Inland Empire, followed by
stronger and more widespread northeast winds Monday and Tuesday. A
strong upper ridge builds over CA through Monday with heights
increasing from 582 dm this morning to 596 dm Monday. This very warm
airmass will bring hot weather to all areas, with added heat in the
Inland Valleys and Coastal areas due to the contribution of
adiabatic warming from downslope flow. Coastal and Valley highs of
95-105 with some spots between 105-110. Beaches will be 80s.

*From Previous Discussion*

High pressure aloft will begin move westward to a position off the
California coast beginning Wednesday with a trough of low pressure
developing over the interior western states for the latter half of
the week. A cooling trend is expected to develop on Wednesday and
extend into Friday and Saturday. The GFS and Canadian models are
faster to move this trough of low pressure into the plains on
Friday and Saturday with the ECMWF slower and more amplified over
the Great Basin and southwest states on Friday before moving it
slowly eastward on Saturday. With these scenarios...the cooling
would be less with the GFS and greater for the ECMWF.

&&

.AVIATION...
211600Z...Coast/Valleys...Patchy stratus with bases around 2500 ft
MSL vcnty KSAN should dissipate by 17Z. Otherwise, skies will be
mostly clear with unrestricted vis through Sunday morning. Areas of
northeast winds will occur through/below passes and canyons at times
after 18Z today through Sunday morning, mainly vcnty KONT, KSBD,
KRAL, KSNA, with speeds 15-30 kt with local gusts 35-45 kt. LLWS
will occasionally affect the above airports, though northeast winds
may not surface at KONT and KSNA until Sunday morning.

Mountain/Deserts... Strong and gusty northeast winds will continue
to develop today and continue through Sunday morning. Winds will be
15-30 kt with gusts to 35-45 kt with strongest winds near ridges and
through passes/canyons, especially San Bernardino and Santa Ana
Mountains.

&&

.MARINE...
San Clemente Basin Buoy still had 10 foot seas from long and short
period WNW swells at 8 AM, but the seas will lower later this
morning. Otherwise, no hazardous marine weather is expected through
next Thursday.

&&

.BEACHES...
A short-period northwest swell from 290 degrees and a long-period
northwest swell from 295 degrees will continue today. This will
bring more elevated surf of 3-6 ft and an increased rip current
threat. Although surf lowers somewhat Sunday, rip currents will
still be a concern. A Beach Hazards Statement is in effect through
Sunday afternoon.

&&

.FIRE WEATHER...
UPDATE: Fire Weather Zone 265 (San Gorgonio Pass Near Banning) will
be added to the Red Flag Warning with the afternoon update due to
strong east winds in the pass. No other significant changes.

Hot and dry Sunday through Wednesday with gusty northeast to east
winds and very low humidity. The most extreme combination of heat,
low humidity, and most widespread winds will be Monday and Tuesday.
Winds started in the San Bernardino County Mountains/Inland
Empire/Santa Ana Mountains this morning, and will increase in
coverage and spread into San Diego County tonight and Sunday.
Strongest winds will be during the mornings Monday and Tuesday.

Lowest daytime humidity of 10 to 15 percent this afternoon will
lowering to 5 to 10 percent Sunday, and then to 5 percent Monday and
Tuesday. Poor overnight recovery.

For today and Sunday areas of northeast winds 15 to 25 mph with
gusts to 40 in the mountains lowering into the coastal foothills and
below passes and canyons. Stronger and more widespread winds Monday
and Tuesday with northeast winds 20 to 30 mph with gusts to 50 mph.

Winds weaken Wednesday with some cooling and increasing humidity
spreading inland Thu and Fri.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Fire Weather Watch from Sunday morning through Tuesday afternoon
     for Orange County Coastal Areas-Orange County Inland Areas-
     Riverside County Mountains-Including The San Jacinto Ranger
     District Of The San Bernardino National Forest-San Diego
     County Inland Valleys-San Diego County Mountains-Including
     The Palomar And Descanso Ranger Districts of the Cleveland
     National Forest.

     Red Flag Warning until 6 PM PDT Tuesday for
     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-Santa Ana Mountains-Including The
     Trabuco Ranger District of the Cleveland National Forest.

     Excessive Heat Watch from Monday morning through Tuesday evening
     for Orange County Coastal Areas-Orange County Inland Areas-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Coastal Areas-San Diego County
     Valleys.

     Beach Hazards Statement through Sunday evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...Moede
AVIATION/MARINE/BEACHES...Maxwell



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