Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 240226
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
726 PM PDT Mon Oct 23 2017

...Areas of Strong Gusty Winds Developing Overnight...
...Record-Breaking Heat Again Tuesday...

.SYNOPSIS...
Areas of strong winds will develop overnight through Tuesday
morning in Santa Ana style. Another day of record-breaking heat is
forecast Tuesday. High pressure will prevail throughout the week,
but will weaken. This will lead to a gradual moderation in
temperatures and a relaxation of the Santa Ana winds.

&&

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

...Update...

Record-breaking heat scorched the area today with triple digit
readings over much of the area. The hottest location was Fullerton
in Orange County, hitting 107F degrees. Extremely dry air was
entrenched region wide with min relative humidity in the single
digits and teens uniform over all but the immediate coast. Peak
Santa Ana winds this morning were in the 40-50 mph range, except
Sill Hill in San Diego County recorded a wind gust of 57 mph at
9 AM this morning.

Now to the forecast. The main hazards will be the development of
stronger winds overnight and another day of record-breaking heat
on Tuesday.

The pressure gradient will tighten up overnight with -14mb
projected from San Diego to Tonopah, NV. Global models show H85
winds strengthening to about 25 KT by 12Z Tue. Hi-res models show
strong winds developing in the favored windy locales:
Through and below the Cajon and San Gorgonio Pass, the Santa Ana
coastal foothills (Inland Orange County) and the coastal foothills
and eastern inland valleys of San Diego County.

Current assessment has winds stronger that what occurred this
morning. Thinking is winds by Tue morning will prevail out of the
northeast (winds more ENE in San Diego County) at 20-35 mph with
peak gusts of 50-60 mph. Some cities most likely to experience
the strongest winds include:

Ontario, Rancho Cucamonga, Rialto, Fontana, Beaumont, Alpine and
Ramona. Places like Sill Hill and Freemont Canyon could peak out
at around 70 mph.

The strongest winds will occur at dawn through about 10 AM
Tuesday, but will continue gusty in corridors through the
afternoon, especially through and below the Cajon Pass extending
through the I.E. to the central and southern Orange County coast.
Another potentially favored corridor of gustier ENE winds will be
form just west of Julian through Ramona towards Encinitas.

The heat will be on again Tuesday with more record highs likely.
Increased temperatures along the coast in this update, especially
for central and south Orange County to about Encinitas. Further
south hi-res models show a potential weak eddy which could result
in more onshore winds over southern San Diego County. Tough temp
forecast for the coast. Highest confidence on hot beaches is
across central and southern Orange County where temps should soar
well into the 90s. Inland locales west of the mountains should be
similar to what occurred today due to significant adiabatic
warming/compressional heating on downslope flow. Mountain locales
likely will be a few degrees cooler as temps aloft nudge slightly
lower.

...Previous Discussion (Issued at 153 PM PDT Mon Oct 23 2017)...

Hot and very dry weather will continue through mid-week with
upper-level ridging aloft and surface high pressure over the
Great Basin. H500 heights will peak around 595 DM through
tomorrow over southwest CA. This will create high temperatures
around 10 deg above normal for desert and mountain locations. The
downsloping Santa Ana winds will help create highs 15 to 25 deg
above normal for coastal and valley locations through Tuesday.
Several high temperatures records are expected to be broken or
tied over the next few days. Please see our weather story on our
webpage for the specific temperatures and record information. An
Excessive Heat Warning will continue for the Coasts and Valleys
through Tuesday for highs in the low 100s inland, and the mid-80s
to mid-90s at the beach.

Gusty Northeasterly winds will continue through Wednesday
afternoon in the mountains, valleys and over most of Orange
County. Sustained winds of 15-30 mph with gusts of 40-60 mph are
possible through the period, with strongest winds developing
Tuesday morning though mountain passes and along coastal mountain
slopes. A Wind Advisory remains in effect through the period.
A Red Flag Warning also remains in effect through Wednesday
evening for extremely low relative humidity in the single digits,
gusty Northeasterly winds and hot weather.

The ridge aloft will weaken through the end of the week, but
remain over the region. High temperatures will lower to just above
seasonal normals by Saturday. Returning onshore flow will
increase humidity across the coast and valleys by the end of the
week, and also create the possibility of low clouds and fog along
the immediate coast.

&&

.AVIATION...
232015Z...Clear with unrestricted vis through Tuesday. Areas of
northeast winds 15-25 kt and gusts 35-45 kt will occur at times,
strongest Tuesday morning. Strongest winds will be through and below
the passes and canyons, and on coastal mountain slopes and
foothills. This will produce MDT-STG UDDFS and LLWS over and W/SW of
the mountains. This will impact vcnty KONT, KSBD, KRAL and KSNA at
times. Surface northeast winds will be most likely at those airports
Tuesday morning, though KONT will continue to be northeasterly at
the surface at times this afternoon and tonight as well.

&&

.MARINE...
No hazardous marine weather is expected through Friday.

&&

.BEACHES...
A combination of west-northwest and south swells will bring mostly 3-
6 foot surf at the beaches of Orange County and San Diego County
through Wednesday, along with a high rip current risk.

&&

.FIRE WEATHER...
High pressure aloft and surface offshore flow will create critical
fire weather conditions for areas over and west of the mountains
through Wednesday. Northeasterly wind gusts of 40-60 mph are
possible for portions of the mountains, valleys and areas of
Orange County, with strongest winds occurring Tuesday morning
along coastal mountain slopes. Minimum relative humidity will be
in the single digits for most areas, with poor overnight recovery.
High temperatures will range from 10-25 deg above normal, as well.
A Red Flag Warning remains in effect through Wednesday evening.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 6 PM PDT Wednesday 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 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-
     Santa Ana Mountains-Including The Trabuco Ranger District
     of the Cleveland National Forest.

     Wind Advisory until 2 PM PDT Wednesday for Orange County Coastal
     Areas-Orange County Inland Areas-Riverside County Mountains-
     San Bernardino County Mountains-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Mountains-San Diego County Valleys-Santa Ana Mountains and
     Foothills.

     Excessive Heat Warning until 8 PM PDT Tuesday 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.

PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/JJT (Prev Discussion)
AVIATION/MARINE...SS


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