Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 080450
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
845 PM PST Thu Dec 7 2017

.SYNOPSIS...
A resilient ridge of high pressure over the West will bring gusty
Santa Ana winds and warm weather through the weekend. Weak to
moderate offshore flow will continue all of next week with high
temperatures 5 to 15 degrees above average. No precipitation is
forecast through the middle of December.

&&

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

The exceptionally dry airmass that moved into Southern California
today resulted in a precipitable water of 0.09" on the 12Z NKX
sounding. This is one of the lowest values on record. The dry air
extended all the way to the beaches where at Noon the dewpoint was
an incredible -10F at Imperial Beach, -5F at Montgomery Field, and -
1F at the San Diego Airport. The relative humidities were 3-5%.

The dry, strong ENE winds blasted their way all the way to the coast
today with gusts to 35 mph at North Island and San Clemente Pier. A
peak wind summary is here: goo.gl/ixZue3

Offshore winds were still quite strong this evening with gusts at 8
pm of 66 mph at Sill Hill, 59 mph at Palomar Mountain, and 50 mph at
Banning. A strong 1044 mb surface high over Utah only weakens to a
1040 mb surface high on Friday, so tomorrow will be another day of
strong gusty winds again. They won`t be quite as strong as today,
and mainly confined to the mountains, passes and eastern valleys. A
High Wind Warning remains in effect for the mountains, valleys, San
Gorgonio Pass and all of Orange County through 4 pm Friday.

A notable change for tomorrow will be the return of an onshore sea
breeze in the coastal zones in the morning, spreading into the
valley zones in the afternoon. This shift from offshore to onshore
winds is another hazard the firefighters will have to contend with.

There are no changes to the long range forecast. The resilient ridge
over the west will remain in place through next week with warm, dry
weather and offshore flow.

*From Previous Discussion*

The surface high over the Great Basin will weaken by this weekend,
however breezy to gusty offshore winds will continue for inland
areas through the middle of next week. Upper-level heights building
over the region will create high temperatures 5-15 degrees above
seasonal normals through the middle of next week.

Models are in disagreement in the placement of the upper-level
ridge for the end of next week, with some showing the ridge
anchored over SoCal, and some showing it well off the West Coast.
Models are also hinting at an upper-level low developing to our
south, which could reinforce additional days of offshore winds.
No sign of low stratus or precipitation for the next 7 days.

&&

.AVIATION...
080400Z...VFR will prevail through the TAF period under a mostly
clear sky. Winds will be less than 10 KT tonight, except 10-15 KT
and gusty at KONT. STG UDDFS/LLWS over and W or SW of the mountains.
Winds on Friday will become onshore as a sea breeze develops, then
will become light or even out of the NE at KONT at near 10 KT.

&&

.MARINE...
The strong offshore winds have diminished over the marine areas, so
the Small Craft Advisory has been cancelled. No marine hazards are
forecast.

&&

.FIRE WEATHER...
Extreme fire conditions through Sunday with strong winds and low
humidities in the mountain passes, foothills and eastern valleys.
Peak gusts each morning through mid afternoon will range from 30-50
mph with a few gusts near 65 mph. Relative humidity will be below
10%.

An onshore sea breeze will move into the coastal zones Friday
morning and across the inland valleys in the afternoon, impacted the
Lilac and Liberty Fires. The winds will range from 8-16 mph, and may
result in erratic fire behavior during the time of the wind shift.

The dry offshore flow pattern with a dominant surface high over the
northern Great Basin will be in place through the middle of next
week. Humidities will remain very low, temperatures will be way
above average by 10-15 degrees, and weak to moderate offshore flow
will continue.

The Red Flag Warning remains in effect through 8 pm Sunday for most
areas, the exception is coastal Orange County where it expires at 8
pm Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning until 4 PM PST Friday 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-San Gorgonio Pass
     Near Banning-Santa Ana Mountains and Foothills.

     Red Flag Warning until 8 PM PST Sunday 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 Coastal Areas-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.

     Red Flag Warning until 8 PM PST Saturday for Orange County
     Coastal Areas.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...Moede
AVIATION/MARINE...Gregoria



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