Heat Advisory 3, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
236 AM PDT Thu Jul 6 2017

.SYNOPSIS...
High pressure will bring warmer weather through Saturday,
followed by minor cooling early next week. Southeasterly flow
will also bring some showers and thunderstorms, mainly to the
mountains during the afternoons. Marine layer low clouds will be
patchy and restricted to the coastal areas, with little if any low
clouds over the weekend.

&&

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

Patchy low clouds were along the coast with a few mid and high
clouds moving north over the inland areas this morning. Low clouds
will be even less widespread tonight into Friday morning, then for
the most part dissipate over the weekend.

The warming trend will continue today as an upper level high
strengthens over the Four Corners region, with 500 mb heights
peaking at an impressive 600 dm. Mid and high level moisture will
increase under south-southeast flow aloft. The base of the
moisture plume will be slightly lower and instability increases,
giving us a better chance of convection developing over the
mountains this afternoon, at least over the higher peaks. The sub-
cloud layer remains very dry, so again the main threats will be
dry lightning and gusty outflow winds. For Friday and
Saturday...the upper high shifts west and remains quite strong,
bringing hot conditions inland. The Excessive Heat Watch has been
upgraded to a warning in the deserts and Inland Empire for Friday
morning through Saturday Evening. Head Advisories have been issued
for the mountains below 5500 ft and inland portions of the San
Diego County Valleys, also valid Fri morning through Sat evening.
Saturday looks to be the hottest day, when highs could climb
into the 115-120 range in the low deserts, and 105-110 in the high
deserts and Inland Empire, locally up to 115 in the hottest spots.
Highs in the San Diego County Valleys will be around 95-105.

As the high expands over Southern California, the deeper layer
moisture will be shunted southward with mid-level drying,
especially on Saturday. Precipitation chances decrease each day,
but there remains enough instability that a couple showers and
thunderstorms over the mountains are possible.

The high begins to weaken and lift northeast just enough for the
flow aloft to turn more southeasterly, bringing another influx of
moisture Sunday and Monday. This will bring some cooling with
increasing potential for thunderstorms over the mountains and high
deserts. An inverted trough rotates northward around the west
side of the ridge, though at this time it appears any lifting and
instability with this wave will be too far west to bring us
nocturnal thunderstorms. Flow aloft turns northwest Tue and Wed,
ushering in drier air. There may be enough residual moisture
Tuesday for some cu buildups and isolated showers over the
mountains Tuesday, but Wed looks dry. Otherwise expect minimal day
to day variations in temperatures and a return of coastal low
clouds during the nights and mornings.

&&

.FIRE WEATHER...
Isolated thunderstorms will bring a risk of dry lightning and
gusty outflow winds over the mountains each afternoon through the
weekend. Hot and dry conditions near the surface accompanied by
gusty southwest to west winds on the desert mountain slopes each
afternoon and evening will increase fire weather concerns,
especially on Friday and Saturday. Sunday and Monday will be
cooler with increasing humidity in the mountains, however isolated
dry lightning and gusty outflow winds are still a threat.

&&

.AVIATION...
060846Z...Coast/Valleys...Patchy stratus should continue to develop
within 10-15 sm of the coast through 1400 UTC, with bases around 700-
1000 ft msl, tops around 1100-1300 ft msl, and local vis 1-5 sm,
while P6SM vis and FEW clouds AOA 15000 ft msl continues elsewhere.
1400-1700 UTC, any stratus should clear out, resulting in P6SM vis
and SCT-FEW clouds AOA 10000 ft msl which will continue through
07/0600 UTC. 07/0600-1400 UTC, very patchy stratus/fog possible
within 10 sm of the coast, with bases around 400-700 ft msl and tops
around 800-1000 ft msl. However, confidence is low in timing and
occurrence of any BKN/OVC cigs at KSAN, KCRQ and KSNA. Otherwise,
P6SM vis and SCT clouds AOA 10000 ft msl will continue.

Mountains/Deserts...Isolated -TSRA likely over the San Bernardino,
Riverside and San Diego county mountains during the 2000 UTC-07/0100
UTC time-frame, with bases around 9000 ft msl, CB tops to 40000 ft
msl, strong up/downdrafts and locally gusty surface winds.
Otherwise, SCT-FEW clouds AOA 10000 ft msl and P6SM vis through
Friday morning.

&&

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

&&

.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 11 AM Friday to 9 PM PDT Saturday
     for Apple and Lucerne Valleys-Coachella Valley-San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Deserts-San Gorgonio Pass Near Banning.

     Heat Advisory from 11 AM Friday to 9 PM PDT Saturday for
     Riverside County Mountains-San Bernardino County Mountains-
     San Diego County Mountains-San Diego County Valleys-Santa
     Ana Mountains and Foothills.

PZ...NONE.
&&

PUBLIC...SS
AVIATION/MARINE...Harrison