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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