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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 150411 AAA
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
910 PM PDT Sun Oct 14 2018

.SYNOPSIS...
Some patchy stratus may occur late this evening along the coast. 
From late tonight through Tuesday, a Santa Ana weather pattern will 
bring strong gusty northeast winds to the mountains, valleys and 
even some coastal areas, along with low humidity and higher 
temperatures. The offshore flow will be much weaker Wednesday 
through Friday, but dry warm weather will continue. Upper low 
pressure could bring a few clouds this weekend.

&&

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

Evening update: Made an update this evening to add a wind advisory 
for Monday for the Coachella Valley, San Diego County Deserts, San 
Gorgonio Pass, and Coastal San Diego County. The winds in the desert 
will be strongest below the south facing slopes and could even 
approach wind advisory level (45 mph) in the Coachella Valley. The 
winds in Coastal San Diego County will be strongest (35-40 mph) 
north of Encinitas towards Camp Pendleton where Santa Ana wind will 
surface out of the northeast. Winds will likely remain below 
advisory level in the City of San Diego although still gusty at 
times throughout the day Monday. 

Have also added blowing dust in areas of strong winds especially for 
the Northern Inland Empire where blowing dust could create impacts 
to travel during the strongest winds. There could also be some 
blowing dust/sand concerns in the lower deserts immediately below 
the south facing slopes. 

Other than the above changes the forecast remains on track with a 
strong offshore gradient developing late tonight, continuing through 
Tuesday. The strongest winds will be likely late tonight through 
Monday, although periods of strong winds will be likely through 
Tuesday although not quite as strong. The strongest winds will be 
likely below the Cajon Pass and in the Santa Ana Mountains where 
gusts as high as 80 mph will be possible in the more remote 
locations, and gusts of 60 mph are forecast for populated areas, 
which could cause damage to trees and property.

The remainder of the previous forecaster discussion issued at 200 pm 
Sunday afternoon remains valid below: 

The big change will occur late tonight and early Monday as a Santa 
Ana wind event develops. Winds will gradually increase from the 
northern mountain crests a little after midnight tonight south and 
southwest through the coastal foothills and valleys, including 
through and below passes and canyons. Winds likely will not arrive 
in the San Diego County Valleys until after sunrise Monday. 
Strongest support aloft will be late tonight and Monday morning, 
with high-resolution models, including the local WRF and Cansac WRF, 
indicating gust potential between 70 and 80 MPH in the strongest 
locations, mainly below Cajon Pass and in the Santa Ana Mountains in 
the 4 AM-noon PDT time range Monday. San Diego County should have 
somewhat weaker winds than farther north, with peak gust potential 
around 50-55 MPH in strongest locations. There will be much less 
support for strong winds Monday night and Tuesday, but local gusts 
over 50 MPH will still be possible Tuesday morning. Humidity will be 
low due to the offshore flow, below 10 percent at times. 
Temperatures will be higher once the offshore flow arrives with 
mostly 80s west of the mountains starting Monday.

The upper low which will move through the region from north to south 
Monday will remain over the SW US the rest of the week, with the 
interior SW being the most likely location of the low. This will 
keep us on the back side of the low with NE flow aloft and mostly 
weak offshore flow at the surface. Some model runs have the upper 
low moving west towards So-Cal or northern Baja next weekend which 
could enhance the offshore flow again, though that is dependent on 
the track of the low. Some moisture wraps around the low, based on 
the 12Z GFS solution, and that could even bring some precipitation. 
12Z ECMWF has some precip just to the north and east of our area. 
Have not added any precip for next weekend, but if models continue 
to show some precip in or near our forecast area, then I will add 
that to the forecast package Monday. MOS guidance shows it could be 
quite warm next weekend with 90s possible west of the mountains 
based on GFS MOS.

&&

.AVIATION... 
150200Z....Coastal low clouds will develop after 05Z tonight with 
bases near 2500 ft MSL and spreading 15-20 miles inland, then a slow 
clearing around 10-11Z once offshore winds develop. N-NE winds will 
strengthen tonight with sfc gusts 35-45 kt on the coastal mountain 
slopes and through and below the passes after 06Z, then increasing 
to 45-55 kt by Monday morning and spreading into the valleys and 
Orange County coastal plain. LLWS likely at SBD, KONT, and KSNA 
Monday morning prior to winds surfacing. STG-SVR UDDFS likely over 
and S/SW of the mountains. Gusty sfc winds will continue into 
Tuesday and begin to diminish Tuesday evening. 

&&

.MARINE...
Northeast wind gusts to around 20 kt possible near and northeast of 
San Clemente Island Monday morning through Monday evening. No 
hazardous marine weather is expected Tuesday through Thursday.

&&

.FIRE WEATHER...
Critical fire weather conditions will occur at least Monday and 
Tuesday due to the Santa Ana Winds. Fuels which will be initially 
wet from the recent rains should dry out Monday as humidity will be 
10 percent or less in most low elevation locations, combined with 
winds 20-40 MPH with local gusts 55-75 MPH (Santa Ana Mtns and 
Inland Empire). Strongest winds will be Monday morning with winds 
somewhat weaker Tuesday. Mostly lighter winds are expected Wednesday 
through Friday, though humidity will stay low.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 3 AM Monday to 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 Monday for Coachella Valley-San 
     Diego County Deserts-San Gorgonio Pass Near Banning.

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

     Beach Hazards Statement until 10 PM PDT this evening for Orange 
     County Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory from 6 AM to 6 PM PDT Monday for San Diego County 
     Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...Maxwell/JMB
AVIATION/MARINE/BEACHES...Connolly