182
FXUS66 KSGX 081634
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
934 AM PDT Sun Sep 8 2024

.SYNOPSIS...
Hot conditions will continue into Monday, with well above average
temperatures across the area. There are chances of showers and
thunderstorms in the forecast from the valleys to the deserts this
afternoon. Main impacts from any thunderstorm that develops will be
heavy rain, erratic gusty winds, and frequent lightning. A trough is
expected to move into the western states by the middle of the week,
leading to a quick cooling trend, drier weather, a deeper marine
layer, and areas of gusty winds.

&&

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

At 9 AM, temperatures at the coast were running a few to 5 degrees
warmer than yesterday morning with temperatures a few miles inland
and in the valleys running 5 to 10 degrees warmer than yesterday
morning. In the mountains and deserts, conditions were similar to a
few degrees cooler than yesterday. Hot conditions are on track to
continue into Monday with the ridge of high pressure over the
Western United States. Highs on Monday for the coast and valleys
will still be 10 to 15 degrees above average. Highs in the mountains
and deserts will be 5 to 10 degrees above average. High pressure
aloft is suppressing the marine layer, preventing that cooler
marine air from moving inland. As the ridge weakens and gets
pushed to the west due to a trough moving into the Pacific
Northwest, the marine layer will be allowed to deepen and rebuild.
Low clouds and fog are expected to make their return to coastal
areas and potentially into portions of the valleys around mid-
week.

An inverted trough over northwestern Mexico will provide light east
flow aloft with continued monsoonal moisture. Highest confidence for
thunderstorm development is along the mountains drifting into the
high desert and Inland Empire again today per latest HRRR/WRF
models. Some thunderstorms may drift into the eastern valleys of San
Diego county as well. We can expect the heaviest rainfall in the
mountains with rates 0.50 to 0.75 inches per hour, some ensemble
members of the HREF are indicating localized rates of 1 inch per
hour are possible. Areas of flash flooding are possible where
thunderstorms develop, especially in the mountains. Gusty and
erratic downburst winds are possible where thunderstorms develop.
Available moisture will begin to decrease Monday with the trough
looming to the north and the high weakening. High resolution
convective allowing models are indicating isolated shower and
thunderstorm activity Monday, and the current forecast has a 15 to
35 percent chance across the mountains. After Monday, no
thunderstorm chances remain in the forecast.

By Wednesday the deep trough axis moves over the West Coast. This
will significantly cool our region from 10-15 degrees above average
today to up to 10 degrees below normal for the middle of the week.
Thursday cools even further and will be crowned the coolest day of
the week. With the exception of the lower deserts, locales will see
high temperatures from the upper 60s to mid 80s. Chances are low to
moderate that lower desert locations see triple digit readings.
Winds will also increase across the passes and adjacent deserts with
this cooling nearing 30-45 MPH at times. The marine layer will build
through the week as well, providing better low cloud and fog
development near the coast and and into the valleys each evening to
morning. Ensemble model clusters indicate broad troughing continuing
across our area by later this week, which will keep temperatures
near to slightly below normal readings for mid September.

&&

.AVIATION...
081430Z...Coasts...FEW-SCT clouds at/above 12,000 ft MSL and local
vis restrictions in FU/HZ near the Roblar Fire through Monday
morning. Very low (5-10%) chance of fog developing along the
southern San Diego County coast between 09-16z Monday.

Valleys/Mountains/Deserts...20-50% chance of TSRA across the
mountains, foothills, Inland Empire, and deserts 18-02Z today with
the highest chances across the mountain ridges and coastal mountain
slopes. Reduced visibility in RA/small hail, strong up/downdrafts,
and gusty outflow winds likely VCTY TSRA, including near KRIV and
KHMT. CB bases 10,000-12,000 ft MSL and tops to 35,000 ft MSL.
Otherwise SCT clouds at/above 12,000 ft MSL and reduced visibility in
FU/HZ near the Line Fire, including at KSBD.

&&

.MARINE...

No hazardous marine weather 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...Heat Advisory until 8 PM PDT Monday for Orange County Coastal
     Areas-San Diego County Coastal Areas.

     Excessive Heat Warning until 8 PM PDT Monday for Orange County
     Inland Areas-San Bernardino and Riverside County Valleys-
     The Inland Empire-San Diego County Valleys-Santa Ana
     Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE...Munyan