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000 
FXUS66 KSGX 190351
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
851 PM PDT Thu Oct 18 2018

.SYNOPSIS...
High pressure building over the Great Basin will bring warm, dry 
weather through Saturday. This Santa Ana pattern will also bring 
gusty offshore winds to the mountains, foothills and inland valleys. 
On Sunday and Monday an upper level trough moving inland through 
central California will bring some clouds to the mountains and 
deserts. It will also bring back night and morning low clouds and 
fog to the coastal and valleys areas. 

&&

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

...Update....
 
Another day of a crystal clear sky and warm temps prevailed across
Southern California as offshore flow continues. Highs today ranged
from 56 at Baldwin Lake to 92 at Lake Forest. This trend will
continue on Friday with the hottest readings west of the
mountains as a Santa Ana revs up late tonight through Friday with
NE-E winds of 20-30 mph and gusts to around 45 mph through and
below the passes and canyons, foothills and into the IE and Orange
County. No changes were made to the forecast this evening.

...Previous Discussion (Issued at 145 PM PDT Thu Oct 18 2018)...

The current Santa Ana weather pattern will bring clear skies and 
warm days Friday and Saturday. Downslope adiabatic warming will push 
high temperatures into the low to mid 90s in the Inland Empire and 
Inland Orange County. Coastal zone highs will be in the 80s as will 
the San Diego Valleys. Mountain highs will range from the 50s-70s, 
depending on elevation, the high deserts will be in the upper 70s, 
and the low deserts from 88-93. This is one of those scenarios where 
the highest temperature in our region will be in the IE or Orange 
County instead of the lower deserts on Friday. 

The warm, dry weather combined with the gusty northeast Santa Ana 
winds from 15-30 mph with gusts to 45 mph in the mountain passes, 
foothills and valleys will elevate fire weather concerns. A Red Flag 
Warning will be in effect from 3 AM to 10 PM Friday. Somewhat 
lighter winds and better humidity recovery is expected on Saturday.  

On Sunday the synoptic pattern changes. A trough of low pressure 
will move inland across California bringing some cooling, onshore 
flow and the return of marine layer clouds to the coast. Low clouds 
will first arrive Saturday night at the coast, initially low enough 
for possible pockets of dense fog in a few places. But a coastal 
eddy spins up Sunday morning that will lift the cloud bases and 
allow the low clouds to move several miles inland across the coastal 
zones. 

The trough will draw modest amounts of moisture in from the 
southeast, primarily over the mountain and desert areas where the 
Precipitable Water increases to 0.75". Most of the precipitation 
will likely remain over the eastern San Bernardino and Riverside 
County deserts. 

Monday through Friday: The trough drifts east and is replaced by 
weak ridging aloft for dry, mild weather next week. Temperatures 
will be a little above average for the fourth week of October. 

&&

.AVIATION... 
190330Z...Skies will remain clear throughout the period, with no 
cigs or vis restrictions. N/NE Winds will pick up significantly 
starting 09-10Z Fri, and will peak near midday. Peak winds 15-20 kts 
gusting to 30 kts are likely at KONT and KSBD, with KSNA, KPSP, KTRM 
and KSAN about 5-10 kts lower. Winds will remain quite STG overnight 
Fri with gusts to 15-20 kts expected at most terminals through noon 
Sat. Pockets of MOD-STG UDDFS are likely on leeward side of mountain 
ridges, above the foothills. An isolated pocket of LLWS cannot be 
ruled out during the wind onset and dissipation periods, but should 
not be widespread given that low-levels should remain well-mixed.

&&

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

&&

.FIRE WEATHER...
A Red Flag Warning will be in effect from 3 AM to 10 PM Friday. 
Northeast winds will be strongest in the passes, foothills and in 
the Inland Empire below the Cajon Pass. Lowest daytime humidity will 
be from 10 to 15 percent. 

On Saturday there will be slightly better humidity recovery with 
lowest RH around 20 percent. The winds will also be a little 
lighter. 

Onshore flow will return Sunday into early next week with a cooling 
trend for coastal and valley areas and a further recovery in 
humidity.

&&

.SKYWARN... 
Skywarn activation is not needed. 


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 3 AM to 10 PM PDT Friday 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.

PZ...NONE.
&&

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