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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 161627
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
927 AM PDT Tue Oct 16 2018

.SYNOPSIS...
Offshore flow will continue this morning, but with northeast 
winds not as strong and widespread as on Monday. The winds 
will weaken during the afternoon. Periods of weaker northeast 
winds will continue at times into the weekend. Areas near the 
coast will cool a little today and Wednesday, with inland warming
into Saturday. For Sunday into Monday, a weak upper level low 
pressure system off the southern California coast could bring
increasing clouds and a slight chance of showers and thunderstorms.

&&

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

This morning...Sfc pressure gradients remain offshore but are
trending weaker, with -6.7 mb SAN-TPH and -0.1 mb SAN-TRM. So far,
three locations have reported peak wind gusts of 50-60 mph. We
expect that winds today will be generally weaker and less
widespread than yesterday. Humidity recovery was marginal
overnight and this afternoon could reach single digits in most 
areas.

Through Thursday...The upper level low pressure centered over 
Arizona will slowly weaken and be centered over Utah by Thursday.
A the same time, the sfc high over the Great Basin will move
eastward. This will result in weakening offshore flow across 
southern California.

The northeast winds will mostly diminish during the afternoon. 
Periods of weaker and more localized northeast winds will continue
for Wednesday and Thursday. 

With the weakening offshore flow and decreasing lower level cold
advection from the Great Basin, high temperatures near the coast
will decrease a little today and Wednesday while areas farther 
inland warm several degrees today and a few more degrees on 
Wednesday. High temperatures on Thursday will be even a degree or
two warmer.

Friday through Monday...Weak upper level low pressure will 
develop off the southern California coast on Friday and remain 
through Sunday, then begin to move slowly inland on Monday. The 
upper level low pressure could draw some mid level moisture 
westward into portions of southern and central California for 
Saturday night into Monday. Model solutions continue to favor 
relatively greater chances for showers and isolated thunderstorms 
for San Bernardino, Riverside, and Imperial Counties and lesser 
chances for areas farther west. 

Some additional warming is expected for Friday and Saturday with 
continuing mostly weak offshore low level flow with gusty 
northeast winds near the coastal foothills. For Sunday into 
Monday, greater cloud cover would bring some cooling. 

There is less cold air aloft with this low pressure system than
with the one at the end of last week. High temperatures on Sunday
and Monday should be closer to seasonal averages than last 
Saturday and there should be less potential for thunderstorms than
last Friday night and Saturday.

Chances for precipitation decrease as the upper low moves
northeast late Monday into Tuesday.

&&

.AVIATION...
161600z... Clear skies expected through tonight. Offshore winds will 
continue through this afternoon, before weakening this evening. 
Strongest winds will be through 20Z today in the valleys, mountains 
and in Orange County at 20-30 KT with top gusts over 40 KT. Isolated 
gusts 55-60 mph possible in wind-prone mountains and passes. LLWS 
possible this morning as the winds surface, as well as this evening 
around 21-02Z as winds diminish. MOD UDDFS on coastal mountain 
slopes through this evening.

&&

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

&&

.FIRE WEATHER...
The Red Flag Warning continues through 8 PM this evening for the
mountains, valleys, and Orange County. Critical fire weather 
conditions will continue with periods of gusty northeast to east 
winds and very low humidity.

Northeast winds this morning in San Diego County will be similar
in strength to those on Monday, but a little less widespread.
Northeast winds in Riverside, San Bernardino Counties will not be
as strong this morning as on Monday and will be a little less
widespread. The northeast winds will mostly weaken during the 
afternoon. While there has been modest humidity recovery 
overnight with some areas reaching 20 to 30 percent, the humidity 
will fall to around 10 percent from mid morning through the 
afternoon. 

For Wednesday and Thursday, northeast winds will be significantly
weaker and less widespread with a steady increase in humidity.

&&

.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 this evening 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.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...Connolly/JJT