Wildfire in California, July 23 to 26, 2018

Area Forecast Discussion
National Weather Service San Diego CA
211 PM PDT Mon Jul 23 2018

.SYNOPSIS...
Very strong high pressure aloft will bring very hot weather to
the region through Thursday. The extended heat wave will bring
the hottest days on Tuesday and Wednesday. The lower deserts will
reach around 120, and hottest parts of the Inland Empire will
exceed 110 and over 105 for inland San Diego County valleys. Only
the immediate coast and highest mountains will be mild. The upper
high will suppress most monsoon cloud development but it will
remain muggy along the coast due to the warm ocean temperatures. A
cooling trend is expected to start on Friday as upper level high
pressure weakens slightly and shifts northward allowing monsoon
moisture to return for this weekend.

&&

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

The heat wave has begun and will last through Thursday with
intense heat. 500 mb heights are now 596 DM over Socal which is
strong for anytime of year. This is forecast to increase to
598-599 Dm through Wednesday. The air mass 850 mb temperatures of
28-30 C today peak at 30-33C on Tuesday and Wednesday and only
drop 1C on Thursday. This is the potential temperature we could
reach for full mixing and sunshine and limited monsoon moisture.
We are already seeing temperatures soar to 118F in the Coachella
Valley and 105 to 109 in the Inland Empire hottest locations.
Temperature records date back to the big heat wave of 2006 and
another in 2016. There should be numerous records broken through
Thursday and for Wednesday has some that could be shattered. The
upper high is working to suppress the cumulus growth from the
residual monsoon moisture. Dewpoints are in the 60s to 70 at the
coastal and inland valley areas, largely from the warm sea surface
temperatures that are in the lower 70s, and are mixing out in the
50s for the Coachella Valley due to less monsoon influence. Not
quite a dry air mass but moderate for July and muggy for the
coast. Low temperatures will creep up next 3 nights many areas or
hold steady with the good radiational light wind and mostly clear
skies conditions allowing a drop near sunrise each day, except
very warm for thermal belts and deserts.

Overall have increased maximum temperatures today through
Thursday. Hottest locales could reach 122F given the air mass
potential and moderately dry air and full sun. Its a little
bit of toss up but Wednesday offers the best chances for highest
temperatures in most areas as 598 DM heights (high dome) are
overhead. The flow aloft is near zero on Wednesday and does not
develop southerlies aloft until late Thursday. On Friday we have
a cooler air mass by 1 to 2C but also have potential more marine
influence and also low level moisture surge into the lower
deserts.

The upper high is forecast to nudge north and weaken slightly and
this allows an open door and increased southeast flow aloft for
monsoon surge this weekend...especially on Sunday. Air mass cools
slightly but cloud cover and moist convection will be the big
change. Active thunderstorm days are possible Sunday through
Tuesday. Some activity could spread to inland valleys. This
monsoonal flow will hold temperatures down further but muggier for
deserts.

Next week we are not out of the woods as upper high is forecast to
build back again over northern Arizona and gradual warming trend
but not nearly as strong.

&&

.AVIATION...
232010Z...Coast/Valleys...Mostly clear, except for SCT-BKN009-013
near the coast late tonight about 12Z-16Z. The risk of BKN low clouds
tonight at KSAN is low, so the confidence in the forecast of
no BKN low clouds at KSAN in the TAF is moderate to high.

Mountains/Deserts...Isolated TSRA over the mountains this afternoon
and evening with surface gusts to 35 knots in any storms that do
form.

&&

.MARINE...
West-northwest winds with gusts to near 20 kt over the outer waters near
San Clemente Island this afternoon and evening. No hazardous marine
weather elsewhere.

&&

.Beaches...
A High Surf Advisory is in effect through Wednesday. A long period
16-19 second south-southwest swell from 200 degrees will bring high
surf through Wednesday. The highest surf will be on the
southwest facing beaches of Orange and Northern San Diego Counties
where waves of 5-9 ft are likely. The surf and swell will gradually
lower Thursday. Sea surface temps at beach are upper 60s and lower
70s.

.AVIATION...
232010Z...Coast/Valleys...Mostly clear, except for SCT-BKN009-013
near the coast late tonight about 12Z-16Z. The risk of BKN low clouds
tonight at KSAN is low, so the confidence in the forecast of
no BKN low clouds at KSAN in the TAF is moderate to high.

Mountains/Deserts...Isolated TSRA over the mountains this afternoon
and evening with surface gusts to 35 knots in any storms that do
form.

&&

.FIRE WEATHER...The extended extreme heat and low humidity for
mountains brings elevated wildfire danger through Thursday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 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.

     High Surf Advisory until 9 PM PDT Wednesday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Heat Advisory until 8 PM PDT Thursday for Orange County Coastal
     Areas-San Diego County Coastal Areas.

PZ...NONE.
&&

PUBLIC/FIRE WEATHER...Tardy
AVIATION/MARINE...Small