Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 182047
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
145 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...

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...
182030Z...Clear skies, unrestricted visibility and generally light
winds through tonight. Winds will begin to pick up in the mountains,
foothills and valleys Friday morning with N to NE winds 30-40 mph
and gusts to 50 mph. LLWS likely Friday at KONT and KSBD 07-11Z and
at KSNA 09-13Z as winds begin to surface. MOD-STG UDDFS on coastal-
facing mountain slopes. Winds will begin diminish around 02Z
Saturday.

&&

.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 will not be needed today.

&&

.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.

&&

$$

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


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