Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 221112
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
412 AM PDT Tue Oct 22 2019

.SYNOPSIS...
Hot and very dry conditions will continue today with gusty
northeast winds near the coastal slopes of the mountains. Offshore
flow will weaken on Wednesday with high temperatures west of the
mountains not quite as hot. Stronger offshore flow is expected to
develop late Wednesday night, peak Thursday, with offshore flow
continuing into Friday. A large trough of low pressure over the
western states will bring cooling for Sunday into early next week
with a slight chance showers along and west of the mountains.

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

High pressure aloft and weak offshore flow will bring additional
warming today, especially for coastal and valley areas. Higher
terrain in coastal areas, inland Orange County, and much of the
San Diego County valleys will warm into the mid 90s to 102 today
with a Heat Advisory in effect from 11 AM to 5 PM today. Gusty
east to northeast winds will continue along the coastal slopes of
the mountains into adjacent foothill areas and below passes and
canyons this morning with strongest gusts to around 40 mph. More
localized east to northeast winds will continue through tonight
into Wednesday morning.

With weakening of high pressure aloft and offshore flow, there
should be at least slight cooling on Wednesday for coastal and
valley areas with 5 to locally 10 degrees of cooling in some
inland coastal and western valley areas.

Another round of stronger offshore flow is expected to develop
late Wednesday night and peak Thursday, with offshore flow
continuing for Thursday night into Friday. There remain
differences among the global models with how much and how quickly
the winds will weaken on Friday. The GFS and its ensemble members
are faster with the weakening of the offshore flow with the
current forecast leaning toward the models that are slower with
the weakening. The offshore flow will weaken further on Saturday
with cooling beginning to spread inland as weak onshore flow
returns near the coast.

For Sunday into early next week, high pressure over the eastern
Pacific will amplify with a downstream trough of low pressure
over the western into the central states. This will bring stronger
onshore flow on Sunday with greater cooling spreading inland.

There remains a decent amount of spread in the details of the
trough of low pressure over the western states for early next
week. For southern California, it should be cooler. But beyond
the cooling, the range of solutions is anywhere from dry and
breezy to breezy with a chance of showers along and west of the
mountains. The current forecast mostly uses the NBM PoPs for
Monday and Tuesday to account for the uncertainty with a slight
chance of showers along and west of the mountains.

&&

.AVIATION...
220900Z...Clear skies today and tonight. Local northeast winds 15-25
knots with gusts to 30 knots will occur through 19Z, mainly in
foothills, below passes and canyons, and locally into the Inland
Empire. LLWS and moderate up/downdrafts are possible over and
west/southwest of the mountains.

&&

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

&&

.FIRE WEATHER...
Weak offshore flow will continue today with lowest inland humidity
around 10 percent. Gusty northeast winds will continue along and
below the coastal slopes of the mountains this morning, becoming
weaker and more localized during the afternoon.

Offshore flow will continue to weaken on Wednesday with weaker
winds and with lowest inland humidity recovering slightly to 10 to
15 percent.

Another round of stronger offshore flow is expected to develop
late Wednesday night and peak Thursday, with offshore flow
continuing for Thursday night into Friday. The winds are expected
to be strongest and most widespread on Thursday with less
certainty on how much and how quickly the winds will begin to
weaken for Thursday night and Friday. Lowest inland humidity will
fall to 5 to 10 percent each day with poor overnight recovery.
Critical fire weather conditions are expected to develop on
Thursday and continue into Friday for the mountains, valleys, and
inland Orange.

Very dry conditions will continue into Saturday but with weaker
winds. A greater recovery in humidity is expected on Sunday as
onshore flow strengthens, spreading cooling and higher coastal
humidity inland.

&&

.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 late Wednesday night through Friday
     evening for 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.

     Heat Advisory from 10 AM this morning to 5 PM PDT this afternoon
     for Orange County Coastal Areas-Orange County Inland Areas-
     San Diego County Coastal Areas-San Diego County Valleys.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...17
AVIATION/MARINE...MM


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