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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 182123
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
223 PM PDT Sat May 18 2019

.SYNOPSIS...
Cooler and breezy on Sunday as a cold front approaches and moves 
onshore. Showers and an isolated thunderstorm are expected. The 
snow level will lower down to 6000 ft, with several inches 
possible above 7000 ft. Winds will become quite gusty into the 
deserts. Continued breezy and cool on Monday with showers ending 
early. Another large, cold trough develops over the West by 
Tuesday and slowly weakens through Friday. It will maintain strong
onshore flow, with below normal temperatures, a deep marine 
layer, and a chance for more light precipitation midweek. 

&&

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

At 2 PM, water vapor satellite showed an upper-level low around 
400 miles west of the northern CA coast, with weak ridging over 
southern CA. The aforementioned low will move inland across 
central CA by the end of the weekend, with a cold front moving 
across southern CA Sunday. Increased onshore flow will create 
gusty westerly winds for inland areas, especially over the 
mountains and deserts, on Sunday. This system is looking to have 
enough instability for shower development across most of the area,
and with a deep layer of lower-level moisture present, which will
also help showers develop inland and along the mountain slopes. 
CAPE of 400-800 J/kg will help isolated thunderstorms develop, 
mainly over the coastal waters Sunday morning, then over the 
mountains in the afternoon. 

Rainfall amounts are expected to be one-quarter to one-half inch 
along the Coast, to one-half to one-and-one-half inches in the 
mountains where upslope flow and a threat for heavier convective 
showers exists later in the day. Snow is expected down to 6000 ft,
with several inches possible above 7000FT in the San Bernardino 
and Riverside County Mountains and strong and gusty westerly 
winds will develop Sunday afternoon and evening in the 
mts/deserts. Winds will weaken a bit Monday morning, then
strengthen again late Monday through Tuesday. A Wind Advisory has
been issued from Sunday through Tuesday for portions of the
mountains and deserts, where westerly wind gust of 55 to 65 mph
are possible at times. A Winter Weather Advisory has been issued 
for Monday morning through Tuesday morning for the San Bernardino 
and Riverside County Mountains above 6000 ft. 

The airmass moving in Sunday will be quite cold for this time of
year, with high temperatures expected to be 20 to 35 degrees F
below seasonal normals for inland areas. Several locations are 
expected to break their lowest high temperature record at times 
Sunday through Wednesday.

Only a small break in the active weather is expected late Monday
through early Tuesday, then another system moves inland with a
trough moving across southern CA mid-next week. The enhanced 
onshore flow and deep marine layer generated by this system once 
again threatens accumulating precip along and west of the
mountains and gusty winds for inland areas.

Looking ahead to the upcoming holiday weekend, the 
operational and ensemble means for the ECMWF/GFS still favor a 
trough over the SW. It looks weaker with less cold air, so the 
weather may be dry with temps closer to average for late next week
with a small chance of showers for inland areas on Saturday.

&&

.AVIATION...
182000Z...Coast/Valleys...High clouds AOA 20000 FT MSL through 
tonight. SCT to locally BKN low clouds could redevelop on the coast 
after 05Z, but will likely remain patchy through 10Z Sunday, after 
which OVC low clouds with variable bases AOA 2500 FT MSL will surge 
inland to the mountains. -SHRA starting near 12Z at KSNA and KONT, 
progressing from NW to SE through the morning into early afternoon. -
SHRA chances will be greatest near noon at KSAN. Rain will exit the 
area in the afternoon. Local vis 3-5 mi in heavier showers will be 
possible. 

Mountains/Deserts...VFR will prevail through Sunday morning. OVC 
skies and SHRA will affect the mountains after 19/15Z, with 
strengthening west winds after 18Z Sunday and likely MOD-STG UDDFTS 
and LLWS over and east of the mtns. Low confidence in isolated TSRA 
over the mountains Sunday afternoon.

&&

.MARINE... 
A Small Craft Advisory has been issued for Sunday through Wednesday 
in anticipation of hazardous boating conditions. Expect gusty 
northwest winds this evening over the Outer Waters, increasing in 
strength on Monday, with gusts to 25 kts. Winds will weaken slightly 
Tuesday morning, but likely remain above Small Craft Advisory 
criteria over the Outer Waters, before quickly increasing late 
Tuesday into Wednesday. Gusts may reach and locally exceed 30 kts 
late Tuesday.

Expect high combined seas in addition to the strong winds, with seas 
to 10 ft over the Inner Waters and up to 13 ft for the Outer Waters 
Sunday through Wednesday.  

Showers and possibly an isolated thunderstorm Sunday morning over 
the coastal waters. 

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 5 AM Sunday to 5 AM PDT Monday for 
     Riverside County Mountains-San Bernardino County Mountains.

     Wind Advisory from 11 AM Sunday to 11 PM PDT Tuesday 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 noon Sunday to 3 PM PDT Wednesday for 
     Coastal Waters from San Mateo Point to the Mexican Border 
     and out to 30 nm-Waters from San Mateo point to the Mexican 
     Border Extending 30 to 60 nm out including San Clemente 
     Island.

&&

$$

PUBLIC...JJT
AVIATION/MARINE...Rodriguez