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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 201034
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
334 AM PDT Sat Apr 20 2019

.SYNOPSIS...
A pair of low pressure troughs will move over Southern California
this weekend, ramping up the onshore flow and the marine layer. 
Strong west winds will accompany these systems over the mountains
and deserts, and a few light showers may develop as well, 
especially for western San Diego County. Cooler conditions will
persist this weekend, then warmer next week as high pressure 
builds aloft and onshore winds weaken and trend offshore, sending 
temperatures back into above normal territory. 

&&

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

An upper level trough passing east of San Diego attm is evident 
on water vapor satellite. Surface pressure gradients have peaked 
over the last few hours at 8 to 9 mb from San Diego to Thermal. 
Gusty winds have been noted in the mountains and deserts with peak
gusts in the windiest spots around 40 mph, with gusts to 25 mph 
in the Coachella Valley. The marine layer has deepened as a result
of the onshore gradients and low clouds are affecting most areas 
west of the mountains attm, with patchy drizzle as well, 
continuing through this morning.

Another weak shortwave will zip across California this afternoon 
followed by deepening inside slider tracking over the Great Basin
tonight through through Sunday. This system will generate a 
stronger surface pressure gradient peaking 10 to 15 mb from the 
coast to the Great Basin this evening. A wind advisory will go 
into effect this afternoon through early Sunday morning, when even
stronger winds are likely, with peak gusts in the windiest 
corridors, such as the San Gorgonio Pass, and along the desert 
slopes, up to 60 mph, and in the deserts, including the Coachella 
Valley, up to 45 mph at times, with areas of blowing dust/sand 
possible as well. The series of low pressure troughs will also 
generate a few showers tonight and early Sunday morning out of the
meager moisture profile, with some enhancement from the deep 
marine layer. 

For Monday through mid next week, building upper level ridging 
will bring a warming trend to the temperatures for all areas, 
especially inland valleys and the lower deserts, including the 
Coachella Valley. Expect we'll see a few more 100 degree readings 
by Wednesday through Friday in the lower deserts and Coachella 
Valley. Temperatures in the inland valleys will kiss the 90 degree
mark Tuesday through Thursday, with an approaching series of weak
low pres troughs bringing increasing onshore flow Friday into 
next weekend, with cooler conditions west of the mountains once 
again.




&&

.AVIATION... 
200915Z...Coast/Valleys...Widespread low clouds with bases around
1500 ft MSL already reaching the coastal mtn slopes and obscuring
higher terrain. All TAF sites west of the mtns are expected to 
have cigs through 17Z. Partial clearing, with SCT low clouds 
around 2000 ft MSL, is expected between 18Z today and 02Z Sun. Low
clouds will increase in coverage and spread inland after 03Z 
Sunday.

Mountains...Mostly clear with unrestricted vis through this 
evening. West winds 15-20 kt gusting to 35 kt over the mountains, 
increasing to 20-30 kt gusting to 40 kt after 18Z today. 

Deserts...After 18Z today through Sunday morning...NW winds 
15-25kt gusting to 30 kt at KPSP and KTRM with areas of reduced 
vis in blowing dust.

&&

.MARINE...
A Small Craft Advisory will be in effect over the Outer Waters 
from 10 PM Saturday to 9 AM Sunday for NW winds 10-15 kt gusting 
20-25 kt and combined seas of 7-8 FT. Winds will weaken Sunday 
afternoon. There is a slight chance of showers late Saturday night
into Sunday morning. Otherwise, no hazardous marine weather is 
expected for Monday through Wednesday. 


&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 2 PM this afternoon to 6 AM PDT Sunday for 
     Apple and Lucerne Valleys-Coachella Valley-Riverside County 
     Mountains-San Bernardino County Mountains-San Diego County 
     Deserts-San Diego County Mountains-San Gorgonio Pass Near 
     Banning.

PZ...Small Craft Advisory from 10 PM this evening to 9 AM PDT Sunday 
     for Waters from San Mateo point to the Mexican Border 
     Extending 30 to 60 nm out including San Clemente Island.

&&

$$

PUBLIC...Brotherton
AVIATION/MARINE...PG