Weather Service Report


249 
FXUS66 KSGX 202022
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
122 PM PDT Fri Jul 20 2018

.SYNOPSIS...
Monsoonal moisture will slowly decrease through Saturday with 
isolated afternoon and early evening thunderstorms possible over 
the mountains and high deserts. For Monday through Thursday... 
strong high pressure aloft over the southwest states will bring an
extended period of very hot weather with the heat expected to 
peak on Tuesday and Wednesday. Not quite as hot towards the end of
next week as the high pressure weakens a little bit.

&&

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

Low clouds continuing to cling to the immediate coast in San Diego
and southern Orange County. Weak onshore flow will continue
through Saturday with another round of coastal low clouds likely
tonight and Saturday morning. Meanwhile enough instability and
remnant moisture in place for isolated showers and thunderstorms
over the San Bernardino County Mountains and the High Desert this
evening and again Saturday afternoon and evening. Strong winds
will preclude organized convection however. 

The big story for the weather forecast for SoCal is the long
duration heat wave slated for next week. Although the heat wave is
expected to last from Monday through Thursday and even into Friday
for inland areas, the hottest days (near record see climate
section below) will be Tuesday and Wednesday. The excessive heat
warning remains in effect for all inland areas including the
mountains below 7000 feet. A heat advisory was recently issued for
the entire coastal area, where temperatures in the 90s will be
likely away from the immediate coast. 

As mentioned the peak of the heat wave event will be Tuesday and
Wednesday, but the medium range models are indicating only slight
weakening of the monster upper level ridge over the SW, lowering
H5 heights from about 600 DM to about 595 DM through next weekend.
And as we all know pretty well now, the medium range models
sometimes like to break down the ridge a little too fast in these
heat wave scenarios. Therefore the heat products are in effect
through Thursday, and could conceivably extended to Friday even
for some inland areas. Another important point with this event is
that while the temperatures are not likely to be more extreme than
the event from two weeks ago, the duration will likely be nearly
twice as long, bringing a heightened potential for heat illnesses
for all of the SoCal region. 

&&

.AVIATION... 
201930Z...Coast/Valleys...Low clouds, with bases 1000-1600 ft MSL 
and tops to 1700 ft MSL, will be difficult to clear along the San 
Diego County Coast this afternoon, and may develop along Orange 
County Beaches late this afternoon. Stratus will redevelop along the 
entire coast and move into the valleys tonight with similar tops and 
bases. VIS of 2-4 SM BR is expected where low clouds near higher 
terrain. Low clouds should clear towards the coast by late Saturday 
morning.

Mountains/Deserts...VFR conditions will prevail with some high 
clouds. An isolated TSRA is possible this afternoon over the San 
Bernardinos with CB bases 8000-9000 ft MSL and tops to 35000 ft MSL 
with strong up/downdrafts, local surface gusts over 35 knots, 
lightning and reduced VIS from downpours.

&&

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


&&

.BEACHES...
Swells from the South Pacific will arrive and gradually increase at 
SoCal beaches over the weekend, peaking Tuesday through Wednesday. 
Surf of 6-8 ft could occur along south-facing beaches, along with 
strong rip currents. Surf should diminish Thursday.

&&

.CLIMATE...
Possible record high temperatures for Tuesday based on the 
current forecast temperatures:

Location           Forecast      Current Record
San Diego             86           85 in 2006
Vista                 90           91 in 2000
Chula Vista           84           81 in 2014
Ramona               103          103 in 2006
Alpine               102          102 in 1959
Thermal              117          117 in 2000
Borrego              114          116 in 2014

Possible record high temperatures for Wednesday based on the 
current forecast temperatures:

Location           Forecast      Current Record
Chula Vista           84           82 in 2015
El Cajon              97           99 in 2006 
Ramona               104          101 in 1977
Thermal              118          115 in 2000
Borrego              114          115 in 2000

Several record warm low temperatures are likely as well...especially 
on Tuesday night and Wednesday night.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning from 10 AM Monday to 8 PM PDT Thursday 
     for Apple and Lucerne Valleys-Coachella Valley-Orange 
     County Inland Areas-Riverside County Mountains-San 
     Bernardino County Mountains-San Bernardino and Riverside 
     County Valleys-The Inland Empire-San Diego County Deserts-
     San Diego County Mountains-San Diego County Valleys-San 
     Gorgonio Pass Near Banning-Santa Ana Mountains and 
     Foothills.

     Heat Advisory from 10 AM Monday to 8 PM PDT Thursday for Orange 
     County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.
&&

$$

PUBLIC...Brotherton
AVIATION/MARINE/BEACHES...JJT

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Western Regional Climate Center, wrcc@dri.edu