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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 151709
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1000 AM PDT Mon Oct 15 2018

.SYNOPSIS...
Upper level low pressure over Arizona and surface high pressure
over the Great Basin will bring periods of strong gusty northeast 
winds today, with winds not as strong tonight and Tuesday. The 
strongest winds will be in Orange County and the mountains and 
valleys of San Bernardino and Riverside Counties. Periods of weaker 
and more localized northeast winds are expected Wednesday through 
Friday. Coastal areas will warm and inland areas will cool today. 
Inland areas will be warmer Tuesday through Friday. Upper level low 
pressure could move west off the Southern California coast and draw 
some moisture into portions of Southern California and result in a 
chance of showers and thunderstorms over the weekend.

&&

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

The Santa Ana Winds have arrived in most areas, mainly from NW San 
Diego County and Riverside County north behind a cold front. Highest 
recorded gust so far has been 75 MPH at Fremont Canyon, with 
numerous locations having gusts over 55 MPH. There was patchy fog 
between about 5 AM and 7 AM in the valleys of San Diego County, and 
some cumulus due to a moist unstable layer around 700 MB still was 
occurring in San Diego County ahead of the upper low and cold front. 
The peak of the winds should occur this morning before a gradual 
decrease occurs this afternoon and evening, with a smaller and more 
localized peak in the winds late tonight and Tuesday morning as the 
inversion currently a little above 700 MB will likely lower to 
around 800 MB tonight, which will restrict the strong winds to the 
coastal mountain slopes with much less wind near the coast and even 
in many of the valleys. Humidity is much lower where the offshore 
flow is occurring, below 20 percent in most areas at mid-morning, 
locally below 10 percent. While the temperatures have increased at 
low elevations where the strong winds were occurring, they are much 
lower in the northern mountains, with some 24 hour decreases of 10-
15 degrees in San Bernardino County.

The upper low moving into Arizona will meander over that area 
through late week with a piece of the low moving west towards 
coastal southern California by the weekend. Some moisture will wrap 
around the low, with a likely increase in clouds, probably cumulus, 
Wednesday, then perhaps enough moisture and instability this weekend 
for showers and thunderstorms. With the low-level east flow, chances 
will be best from the mountains east to the deserts, but enough 
moisture could spread west of the mountains, even with the 
downsloping (mostly light) winds, to produce a few showers or 
thunderstorms there. Temperatures will increase in most areas 
Tuesday with warm weather continuing through the weekend, possibly 
in the 90s in some locations by Saturday west of the mountains. The 
only exception would be any places along the coast that get westerly 
low-level return flow.

&&

.AVIATION... 
151600Z....Main issue this forecast period will be winds. Northeast 
winds will continue to strengthen this morning and peak late morning 
through mid afternoon at 15-30 KT. However, some areas particularly 
in foothills, adjacent valleys and Orange County including KONT, 
KSBD, and KSNA will see winds of 20-40 kts with gusts to 60 kts. 
LLWS can be expected anywhere west of the mountains including KCRQ 
until these winds surface. STG-SVR Up/downdrafts likely over and 
S/SW of the mountains. Winds will decrease some late this afternoon 
and evening. Winds will increase again Tuesday morning for a few 
hours, but not as strong as today. No issues with marine layer 
stratus given the presence of offshore flow.  

&&

.MARINE...
Gusty northeast winds mainly near Camp Pendleton this morning, but 
also intermittently anywhere within the stretch between Camp 
Pendleton and San Clemente Island. These intermittent gusts to 25 KT 
or higher would be briefly hazardous to small craft through this 
afternoon. Lighter winds south of a line from Oceanside to south San 
Clemente Island. No hazardous marine weather is expected tonight 
through Friday.

&&

.FIRE WEATHER...
Critical fire weather conditions will continue through Tuesday with 
periods of gusty northeast to east winds and much lower humidity. 
Lowest humidity inland will fall to 5 to 10 percent today and around 
10 percent Tuesday with poor overnight recovery. For San Bernardino, 
Riverside, and Orange Counties from the coastal slopes of the 
mountains to the coast, widespread northeast to east winds of 30 to 
40 mph with gusts to 60 mph are expected for this morning, 
diminishing some to 20 to 30 mph with gusts to 45 mph for tonight 
and Tuesday. Isolated gusts to 80 mph are possible this morning, 
mainly below passes and canyons and near the coastal slopes of the 
Santa Ana Mountains. In San Diego County, the strongest northeast to 
east winds are expected from the coastal mountain slopes into the 
inland valleys with winds of 20 to 30 mph with gusts to 45 mph.

Weaker and less widespread northeast winds are expected for
Wednesday through Friday with a slow recovery of humidity for
inland areas.

&&

.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 8 PM PDT Tuesday 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-Santa Ana Mountains-Including The 
     Trabuco Ranger District of the Cleveland National Forest.

     Wind Advisory until 8 PM PDT this evening for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass Near Banning.

     High Wind Warning until 3 PM PDT this afternoon for Orange 
     County Inland Areas-San Bernardino County Mountains-San 
     Bernardino and Riverside County Valleys-The Inland Empire-
     Santa Ana Mountains and Foothills.

     Wind Advisory from 6 AM this morning to 6 PM PDT this evening 
     for San Diego County Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...Maxwell
AVIATION/MARINE...Moreland