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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
412 
FXUS66 KSGX 191010
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
310 AM PDT Sun Aug 19 2018

.SYNOPSIS...
High pressure aloft over Southern California will transition east
to be positioned over Arizona on Monday, then eventually over 
Texas mid to late week as an upper level trough moves into
northern California and extending southwest over the Pacific. As
the high shifts east, there is a brief opportunity for mountain
and desert thunderstorms Monday and Tuesday afternoon, but that
chance fades mid to late week as much drier air moves into the
area. Temps throughout the week will stay above average, but not
to excessive levels and it will continue humid near the coast with
nighttime and morning low cloudiness. 

&&

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

High pressure aloft currently resides over Southern California.
Global models are in agreement in showing this high transitioning
to the east to be placed over Arizona on Monday then all the way
to Texas during the middle to later part of the week as a trough
moves into NorCal extending southwest into the Pacific. 

There now only looks to be about a two day window where monsoonal
moisture returns to SoCal for afternoon mountain and desert 
thunderstorms. That looks to be Monday and Tuesday afternoon. By 
Wednesday, both GFS and EC now show the local area between a
trough lying to the northwest and ridging centered well off to 
the east with a dry west-southwest flow aloft, shoving the 
monsoonal moisture back to the east. This has been a change from 
model runs 24-48 hours ago, but there now has been some run-to- 
run consistency on this scenario. As such, the forecast was 
trended to reflect isolated-scattered mountain and desert 
thunderstorms Monday-Tuesday with dry weather from Wednesday
onward. Even on Monday-Tuesday, the moisture is not nearly as 
high as our recent monsoonal tstorm episodes, so only isolated- 
scattered tstorms are forecast with a low risk of flash flooding.

Temperatures will continue to run above average through the week
(trough too far away/heights remain rather high locally) and it 
will continue humid near the coast. Gusty west- southwest winds 
will occur especially mid week through passes and from mountain 
ridges to the desert slopes, but doesn't look to reach even 
advisory levels at this time.
  
&&

.AVIATION... 
190950Z...Coasts/Valleys...Areas of low clouds with bases 1200-1700 
feet MSL will continue to develop along the coast and locally spread 
up to 20 miles inland through 15Z. Clouds will clear to the coast by 
18Z. Clouds spreading back inland after 20/03Z with bases 1000-1500 
ft MSL.

Mountains/Deserts...Shallow cumulus clouds may develop over the 
mountain crests during the afternoon, dissipating by sunset. 
Otherwise a few mid and high clouds AOA 10000 ft MSL through Monday 
morning.

&&

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

&&


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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC...Gregoria
AVIATION/MARINE...SS


000
FXUS66 KSGX 191010
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
310 AM PDT Sun Aug 19 2018

.SYNOPSIS...
High pressure aloft over Southern California will transition east
to be positioned over Arizona on Monday, then eventually over 
Texas mid to late week as an upper level trough moves into
northern California and extending southwest over the Pacific. As
the high shifts east, there is a brief opportunity for mountain
and desert thunderstorms Monday and Tuesday afternoon, but that
chance fades mid to late week as much drier air moves into the
area. Temps throughout the week will stay above average, but not
to excessive levels and it will continue humid near the coast with
nighttime and morning low cloudiness. 

&&

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

High pressure aloft currently resides over Southern California.
Global models are in agreement in showing this high transitioning
to the east to be placed over Arizona on Monday then all the way
to Texas during the middle to later part of the week as a trough
moves into NorCal extending southwest into the Pacific. 

There now only looks to be about a two day window where monsoonal
moisture returns to SoCal for afternoon mountain and desert 
thunderstorms. That looks to be Monday and Tuesday afternoon. By 
Wednesday, both GFS and EC now show the local area between a
trough lying to the northwest and ridging centered well off to 
the east with a dry west-southwest flow aloft, shoving the 
monsoonal moisture back to the east. This has been a change from 
model runs 24-48 hours ago, but there now has been some run-to- 
run consistency on this scenario. As such, the forecast was 
trended to reflect isolated-scattered mountain and desert 
thunderstorms Monday-Tuesday with dry weather from Wednesday
onward. Even on Monday-Tuesday, the moisture is not nearly as 
high as our recent monsoonal tstorm episodes, so only isolated- 
scattered tstorms are forecast with a low risk of flash flooding.

Temperatures will continue to run above average through the week
(trough too far away/heights remain rather high locally) and it 
will continue humid near the coast. Gusty west- southwest winds 
will occur especially mid week through passes and from mountain 
ridges to the desert slopes, but doesn't look to reach even 
advisory levels at this time.
  
&&

.AVIATION... 
190950Z...Coasts/Valleys...Areas of low clouds with bases 1200-1700 
feet MSL will continue to develop along the coast and locally spread 
up to 20 miles inland through 15Z. Clouds will clear to the coast by 
18Z. Clouds spreading back inland after 20/03Z with bases 1000-1500 
ft MSL.

Mountains/Deserts...Shallow cumulus clouds may develop over the 
mountain crests during the afternoon, dissipating by sunset. 
Otherwise a few mid and high clouds AOA 10000 ft MSL through Monday 
morning.

&&

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

&&


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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC...Gregoria
AVIATION/MARINE...SS