Wildfire in California, July 13 to 22, 2023

Area Forecast Discussion
National Weather Service San Diego CA
854 PM PDT Thu Jul 13 2023

.SYNOPSIS...
High pressure will strengthen over the Southwest this weekend, as a
weak eddy develops over the California Bight. The eddy could help to
lower coastal temperatures a bit and bring in more low clouds, while
well inland, it continues to warm. The ridge will weaken by the
middle of next week, easing the heat inland somewhat, but the
deserts will still see triple digit temperatures each day. Fire
weather will remain elevated near and below the passes each
afternoon and evening due to gusty west to southwest winds, and in
areas of excessive heat.

&&

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

It was a mostly clear day across SoCal, and this evening, the only
low clouds visible in satellite imagery were over the CA Bight and
along the San Diego County Coast. The robust sfc pressure gradient
from the coast to the lower deserts was supporting wind gusts over
50 MPH through the San Gorgonio Pass and 35-40 MPH below it, into
the northern Coachella Valley this evening. No 00Z Miramar sounding
was available this evening, but recent cloud observations suggest
the marine layer was about 800 FT deep. No forecast updates planned
this evening.

From previous discussion...

High Temperatures on Friday are forecast to be about 5 degrees
warmer than they were today away from the coast. For the mountains,
deserts, and far inland valleys, the heat should peak on either
Saturday or Sunday. High temperatures over the weekend are expected
to be 115-120 for the lower deserts, 110-115 for the Apple and
Lucerne Valleys, and around 105-110 for the more inland portions of
the Inland Empire. By early to mid-next week the heat loosens its
grip a little bit as the high pressure moves from directly over
us off to the east, centering more over Arizona and New Mexico.
Even with the gradual cooling, highs into the middle to end of
next week will still be in that 5 to 10 degree above average
range. NBM keeps high temperatures for Palm Spring above 110 and
in the upper 90s at Ontario through next week.

In addition to above average high temperatures, low temperatures
will also be above average into next week. This will mitigate
overnight relief from the heat. This is most noticeable in the
deserts and mountains where low temperatures are forecast to be 10
to 15 degrees above average. That prevents lows from falling below
70 degrees in the High Desert and mountains, and below the mid-80s
in the low deserts.

For areas closer to the coast, the development of a coastal eddy
should help moderate temperatures a little bit for Friday through
the weekend. By Sunday, some of that cool marine air may make it
into the western valleys which will help moderate temperatures
there. The return of the eddy may also bring patchy low cloud and
fog coverage back to the coast.

&&

.AVIATION...
140330Z...Coast...Mostly clear through Friday evening. Except patchy
low clouds with bases 600-900 feet MSL developing overnight. Cigs
possible and intermittent for coastal TAF sites 10-16Z, with locally
reduced vis of 3-5SM, below 1SM in BR/FG on higher coastal terrain.
Similar low cloud situation Friday night.

Valleys/Mountains/Deserts...Mostly clear through Friday evening. W-
NW winds with sfc gusts 25-35 kt and isolated gusts to 40 kt along
the mtn ridges, desert slopes, and through passes through 11Z. Mod
up/downdrafts over/east of mtns and areas of LLWS.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday.

&&

.FIRE WEATHER...
A prolonged heat wave through early next week should peak
Saturday through Monday, with high temperatures some 10 to 15
degrees above average from the far inland valleys, east into the
deserts. Low minimum RH values of 10-15% each afternoon will
combine with the heat and gusty westerly winds, to elevate fire
weather conditions.

A weak coastal eddy at times this weekend, may bring slow deepening
of a shallow marine layer, which will spread cooler, more humid air
along the coast and into the western valleys.

&&

.CLIMATE...
NBM probabilities for Palm Springs to reach 120 or higher over
the weekend have increased to 86 percent on Saturday and 82
percent on Sunday. NBM probabilities for Palm Springs to equal or
exceed the existing all-time record high temperature of 123 are
greatest on Sunday at 46 percent followed by 25 percent on
Saturday.

The locations most likely to tie or exceed existing high temperature
records over the weekend are in the deserts followed by the
mountains. The locations most likely to tie or exceed record warm
minimum temperatures over the weekend are in mountains and deserts
and some inland valley locations.

...EXISTING RECORD HIGH TEMPERATURES...
         ...PALM SPRINGS...  ...THERMAL...  ...BORREGO SPRINGS...
July 14      119 (2003)        117 (2003)         118 (2005)
July 15      118 (2006)        118 (2019)         117 (2006)
July 16      120 (1998)        118 (1998)         118 (1998)
July 17      120 (2005)        121 (2005)         120 (2005)

NBM probabilities to tie or break the existing high temperature
records for Palm Springs are greatest on Saturday at 92 percent
followed by 82 percent on Sunday and 59 percent on 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 until 8 PM PDT Tuesday for Apple and
     Lucerne Valleys-Coachella Valley-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 Gorgonio Pass Near
     Banning.

     Excessive Heat Warning from 10 AM Friday to 8 PM PDT Tuesday for
     San Diego County Valleys-Santa Ana Mountains and Foothills.

PZ...None.

&&

PUBLIC/FIRE WEATHER...10/CO
AVIATION/MARINE...MM
CLIMATE...17/CO