Dust Devil in California, August 4, 2024

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Sun Aug 4 2024

.SYNOPSIS...
Hot and dry weather will prevail through Monday under high
pressure aloft. Increasing monsoonal moisture will return by mid-
week and bring a 15 to 25 percent chance of afternoon and early
evening thunderstorms in the mountains and deserts, along with
minor cooling. Patchy night and morning low clouds and fog will
continue along the coast. Drier with minor warming Friday and
Saturday.

&&

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

This afternoon...Thunderstorms have developed over the mtn peaks
of northern Baja, several miles south of the border. Some of that
activity could make it's way into the mtns of San Diego County but
the probability is very low that significant tstms will develop owing
to more stable conditions and lower mtn peaks in San Diego
County. Marine layer low clouds persist at some beaches and will
likely spread several miles inland tonight. If the marine layer
gets any shallower tonight, there could be localized dense fog on
higher coastal terrain and mesas late tonight into Monday morning.
Temperatures are a few degrees higher than at this time yesterday
inland away from the marine layer influence.

From previous discussion...
A warming trend will continue through Monday as the expansive
upper level high pressure extends across the southwest U.S. High
temperatures today will be around 5-10 degrees above normal,
increasing to around 7-12 degrees above normal on Monday. This
translates to temperatures in the upper 70s to low 80s near the
coast, upper 80s to mid 90s for Inland Orange County and the
western San Diego County valleys, upper 90s to around 109 for the
inland valleys, mid 80s to low 100s for the mountains below 6500
ft, 102 to 108 for the high desert, and 109-118 for the lower
deserts. With the strong ridging aloft and associated subsidence
as well as the absence of deep-layer moisture, thunderstorm
chances over the mountains remain less than 15 percent for today
and Monday. The marine layer will become even more shallow with
patchy fog at the beaches and locally into the coastal areas each
night and morning.

The west-east oriented ridge axis shifts north of SoCal on
Tuesday, this reduces the subsidence and allows for some minor
cooling and an increase in monsoonal moisture with a 15-20 percent
chance of thunderstorms over the mountains. A weak easterly wave
moves into SoCal on Wednesday, potentially bringing showers or
thunderstorms to areas both on the desert and coastal sides of
the mountains. Details in timing and track of this wave are still
uncertain, and deterministic models are not showing much if any
elevated instability with it, so chances will be low for showers/tstms
not triggered by afternoon heating over the mtns and high desert
on Wednesday.

Gradual drying takes place for the remainder of the week with
lower thunderstorm probabilities over the mountains Thursday
afternoon. Weak ridging across the southern tier of the US with
the potential for more inverted troughs in the vicinity of Baja
California will maintain warm weather with highs a few degrees
above normal for the remainder of the week.

A low pressure trough moving inland off the Pacific Ocean to our
north could bring significant changes for late next weekend but
the details of any changes are highly uncertain at this time.

&&

.AVIATION...
042030Z...Coast...Patchy low clouds move inland this evening and
CIGs develop for most coastal sites by 09z-11z Monday, with bases
600-900ft MSL and tops to 1200ft MSL. Localized VIS reductions to 1-
3SM possible for higher coastal terrain and valleys through 16z.
Confidence in timing of low clouds and VIS restrictions is moderate
(40-70%). Clearing for most coastal sites will occur between 14z-16z
Monday with generally SKC and unrestricted VIS beyond this point.

Valleys/Mountains/Deserts...Satellite shows FEW-SCT Cu near the
mountains with bases to 12,000ft MSL, continuing through 00z.
Generally SKC and unrestricted VIS overnight and through Monday
morning.

&&

.MARINE...
Breezy northwest winds with gusts 15-20kts expected in the outer
waters this evening and Monday afternoon and evening. Otherwise, no
hazardous marine conditions are expected through Friday.

&&

.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 11 PM PDT Tuesday 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 until 11 PM PDT Tuesday for Orange County Inland
     Areas-Riverside County Mountains-San Bernardino County
     Mountains-San Diego County Mountains-San Diego County
     Valleys-Santa Ana Mountains and Foothills.

PZ...None.

&&

PUBLIC...PG
AVIATION/MARINE...Zuber