157
FXUS66 KSGX 280423
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Thu Jun 27 2024

.SYNOPSIS...
Slight cooling will occur in most areas Friday, with the greatest
amount of cooling at night. A warming trend will occur this weekend
and continue early next week, with excessive heat likely in the
deserts again. With high pressure aloft continuing over the region,
the excessive heat will likely continue most of next week in the
deserts, with the high deserts of San Bernardino County having
its highest temperatures the second half of next week with little
change in the lower deserts. Otherwise, fair weather will prevail
with night and morning coastal low clouds and patchy fog
continuing, along with milder coastal conditions.

&&

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

Skies were mostly clear this evening except for developing low
clouds near the coast. The stratus will continue to develop
overnight near the coast and extend into the San Diego County
Valleys with the Inland Empire mostly staying clear. The late
afternoon NKX sounding had precipitable water down to 1.33" from
1.73" 24 hours before, though 1.33" is still above average for late
June. Regardless, impacts continue to be minimal from the moisture
aloft, with only scattered afternoon cumulus over the mountains and
no thunderstorms. Today was the first day since June 22 that we did
not have a record high minimum (morning) temperature, and the
next 2 nights will be near or just slightly above normal west of the
mountains (as well as the day Friday, though with some warming
Saturday), though days and nights will continue to be above normal
in the deserts.

The main weather impact for the next week will be the heat, mainly
in the deserts, and with the expiration of the excessive heat
warning at 8 PM this evening, we issued a new excessive heat watch
for Sunday/Monday for the lower deserts. Current guidance has high
confidence of increasing temperatures through the week in the high
deserts, and some locations in San Bernardino County near Apple
Valley/Victorville could approach 110 the second half of next week
due to the East Pacific upper high building into California/Nevada
and connecting with the west-east oriented southern US/northern
Mexico upper high. Ensembles differ on the details after that, with
some solutions sliding the upper high towards the interior desert
southwest but other solutions keeping it overhead. Regardless, most
solutions suggest temperatures 5-10 deg F above seasonal normals.

From previous discussion...

Pressure heights will continue to rise Sunday into Monday. Chances
for 115 degree readings across the lower deserts increase to
around 30-60 percent by this time per NBM. By Sunday, increased
heat risk will not only be across the deserts but also most areas
away from the coast. Highs in the near or above 100 degrees are
likely for portions of the Inland Empire, with highs in the 90s
across southern mountain areas and SD/OC valleys.

Global ensembles are generally in agreement about high pressure
building into area off the coast by the middle of next week, near
596-600 dm. This would continue the very warm conditions for much
of the week for areas away from the coast. If this does occur,
temperatures will continue to be 5 to locally 10 degrees above
average. Confidence is moderate to high that temperatures will
fluctuate minimally from day to day with warmer overnight low
temperatures as we near the 4th of July holiday.

&&

.AVIATION...
280400Z...Coast/Valleys...Marine layer building in at KSAN with
OVC015 and tops ranging along the coast/valleys between 1500-2100ft
MSL. Marine layer builds in through early Friday morning, with most
coastal airports having BKN-OVC CIGs 1200-1500 ft MSL beginning
between 05-07Z Friday. Localized VIS below 3SM in BR/FG possible in
the coastal valleys overnight. Similar to Thursday morning,
expecting marine layer scattering out beginning around 16-18z
Friday. Synoptic pattern doesn`t look to change much for Friday
evening as marine layer builds in once again beginning around 29/03z.

Mountains/Deserts...Gusty northwest winds continue for parts of the
Coachella Valley, ending by 28/06z. Light and variable overnight
with SKC into Friday morning, with gusty west winds picking back up
late Friday afternoon. Periods of strong gusts through mountain
passes exceeding 40kts at times, and mod up/downdrafts possible in
the vicinity, especially for low-flying aircraft. Some Cu possible
over the mountains Friday afternoon, with bases likely at or above
15,000ft MSL. Gusty northwesterly winds pick back up in the
Coachella Valley beginning between 28/20z-29/02z. Lowering VIS looks
unlikely at this point, but periods of strong gusts may bring
localized blowing dust.

&&

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

&&

.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 Sunday morning through Monday evening
     for Coachella Valley-San Diego County Deserts-San Gorgonio
     Pass Near Banning.

PZ...None.


&&

$$

PUBLIC...Maxwell (Update)/APR (Previous Discussion)
AVIATION/MARINE...Zuber