837
FXUS66 KSGX 301009
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
309 AM PDT Sun Jun 30 2024

.SYNOPSIS...
Warmer today with highs well above normal. A slight cooldown on
Monday will be short- lived before a warming trend sets in across
the region for the rest of the week and into next weekend. A
prolonged period of hot weather will exacerbate any heat impacts
this week. Areas of night and morning low clouds and fog will
continue along the coast and far western valleys through the week.

&&

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

Marine layer low clouds have returned to the coastal areas and
some of the far western valleys in San Diego County with clear
skies elsewhere. Clouds will clear back to the coast by late
morning. High pressure aloft building in from the east today will
bring widespread warming to the region. High temperatures will be
around 5 to 10 degrees above normal, with the greatest departure
from normal in the far inland valleys where highs will be in the
low 100s. Low deserts will see highs of around 110 to 114 degrees,
and the high deserts will be in the low 100s. The marine layer
will help moderate temperatures at the coast into the western
valleys, where highs will be in the upper 70s to around 90. An
Excessive Heat Warning remains in effect for the low deserts.
There is around 10 percent chance of showers and thunderstorms in
the southern portions of the San Diego County mountains and
deserts this afternoon. The 00Z run of the HRRR did show at least
light showers over our area, but later runs now keep any activity
south of the border, so our chances are dwindling.

Brief minor cooling occurs on Monday as an upper trough moves
inland across the West Coast, though high temperatures will remain
a few degrees above normal. The upper level high off the West
Coast very slowly shifts eastward over CA and eventually into the
Great Basin through the week as it steadily strengthens. This will
bring a prolonged heat wave to the region with a degree or two of
warming each day through Thursday, followed by another 2 to 4
degrees of warming on Friday, which is currently forecast to be
the hottest day. Ensemble guidance is still showing a bit of
spread with the placement of the upper high, especially beyond
Thursday, and to a lesser degree, the strength of the high. This
brings in some uncertainty in the high temperature forecast,
though even the lower end of the range is still quite hot. With
the EC ensebmle coming more in line with the GEFS in terms of the
strength of the high, overall temperatures have trended upward for
Fri and Sat. NBM now shows a 22 percent chance of Palm Springs
hitting 120 or more by Friday, increasing to 25 percent on
Saturday. Saturday and Sunday are even more uncertain as there is
the potential for a short wave to drop through the interior west,
pushing the upper high back westward and bringing cooling, or at
least not as hot, weather here, but this only accounts for around
20-40 percent of the ensemble space depending on the day, with the
remaining members having the upper high persisting somewhere
across CA into the Great Basin. The Excessive Heat Warning remains
in place for the lower deserts through Friday, with an Excessive
Heat Watch for the high deserts for Tuesday through Friday.
Additional heat products may be needed for other inland areas
late in the week.

Aside from the heat, some mid-level moisture may make its way in
here around Wednesday as an upper low develops to our southwest.
However, at this time instability is very marginal with strong
capping from the nearby ridge, so thunderstorm chances remain
below 10 percent. Otherwise a continuation of night and morning
low clouds and fog will continue along the coast and occasionally
into the far western valleys as the marine layer persists. The
marine layer and onshore flow each day will help moderate
temperatures at the coast through the week.

&&

.AVIATION...
300850Z...Coast/Valleys...Low clouds increasing in coverage at this
hour. Bases are 900-1100 ft MSL with tops to 1700 ft MSL. Low clouds
could extend 15 miles inland - locally farther - by 14Z. Vis 3-5SM
in fog, with local vis 1SM on higher coastal terrain through 16Z.
Expect clearing to the coast 15-17Z. Low clouds returning to coastal
areas after 06Z Monday with less coverage.

Inland...Westerly winds gusting locally 25-30 knots through Cajon
and San Gorgonio Passes and into adjacent deserts again this
afternoon/evening. Mostly clear skies with unrestricted VIS today
except SCT100 after 18Z, mainly over mountains.

&&

.MARINE...
No hazardous marine conditions are expected 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 Watch from Tuesday morning through Friday evening
     for Apple and Lucerne Valleys.

     Excessive Heat Warning from 10 AM this morning to 8 PM PDT
     Friday for Coachella Valley-San Diego County Deserts-San
     Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...SS
AVIATION/MARINE...PG