Heat in California, August 6 to 9, 2018

Area Forecast Discussion
National Weather Service San Diego CA
917 AM PDT Mon Aug 6 2018

.SYNOPSIS...
Very hot and dry conditions will continue for inland areas through
Tuesday. Monsoonal moisture will begin to return on Wednesday,
bringing higher humidities and a chance of mostly afternoon and
early-evening thunderstorms, mainly in the mountains, deserts,
and inland valleys. For next weekend, a trough of low pressure
moving inland through the Pacific Northwest will bring some drying
and strengthen the onshore flow, with gusty southwest to west
winds in the mountains and deserts each the afternoon and
evening.

&&

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

This morning...A shallow marine layer (about 1000 ft deep) brought
low clouds and patchy fog to the coastal areas overnight. The
clearing process is under way and sunny skies should extend to the
beaches by late morning.

From previous discussion...
High pressure aloft, centered over New Mexico and Arizona will
expand across Southern California, bringing very hot and dry
conditions for inland areas through Tuesday. The marine layer and
weak onshore flow will help to moderate temperatures near the
coast, though sea surface temperatures in the mid to upper 70s
will continue to keep nights warmer near the coast with low
temperatures mostly in the 70s. The local high-resolution model
shows a coastal eddy developing tonight and continuing into
Tuesday. This might bring some patchy low clouds to areas near the
coast late tonight into Tuesday morning.

On Wednesday...monsoonal moisture will begin to return. This will
take the edge off the excessive heat for inland areas and bring a
chance for thunderstorms over the mountains on Wednesday
afternoon and early evening.

For Thursday and Friday...southeast flow between high pressure to
the north centered over Nevada and a tropical cyclone off the
southwest coast of Baja will maintain the influx of monsoonal
moisture into Southern California with continuing chances for
afternoon and early evening thunderstorms for the mountains,
deserts, and inland valleys. Some convection could occur overnight
and spread west of the mountains around Thursday night as a weak
upper level disturbance moves in from the southeast. With weaker
onshore flow, high temperatures for coastal areas could be warmer
for Thursday and Friday than earlier in the week with high
temperatures in the 90s extending almost to the coast.

For next weekend, a trough of low pressure moving inland through
the Pacific Northwest will bring a return of onshore flow and
some slow drying. Medium-range deterministic models show some
differences on the timing of the drier conditions, with the
European model a little faster and the GFS slower.

&&

.AVIATION...
061530Z...Coast/Valleys...Low clouds and fog have quickly burned off
this morning. Less coverage of stratus and fog are expected tonight and
Tuesday morning, and will leave ceilings SCT in the TAFs accordingly.
Haze will affect inland empire terminals with visibilities 4-6SM
during the daytime hours.

Mountains/Deserts...VFR conditions with clear skies and unrestricted
visibilities. Localized gusty northwest winds can be expected
during the evening hours 23-04Z.

&&

.MARINE...
No hazardous marine weather is expected through Friday.

&&

.BEACHES...
Evening high tides will rise to around 7 ft beginning on Wednesday,
peaking at around 7.5 ft on Friday evening. Evening high tides will
remain at or above 7 ft through Sunday. In addition, potentially
large south swells from Tropical Storm John will move into the
coastal waters beginning Thursday and continue through the weekend.
The combination of high tides and elevated to high surf will likely
cause coastal flooding during the late afternoon and evening each
day during this period. The overall impact of the flooding will
largely depend on the swell/surf, which is uncertain due to model
differences in the intensity of the tropical system as it passes
through the swell window.

&&

.FIRE WEATHER...
Very hot and dry conditions will continue for inland areas through
Tuesday with lowest daytime humidities of 5 to 10 percent in the
inland valleys, mountains, and deserts with a slight increase in
the lower deserts on Tuesday. Monsoonal moisture will begin to
return on Wednesday bringing higher humidities and a chance of
mostly afternoon and early evening thunderstorms, mainly in the
mountains, deserts, and inland valleys.

&&

.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-Orange County Inland Areas-
     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 Diego County Valleys-San Gorgonio Pass Near Banning-
     Santa Ana Mountains and Foothills.

PZ...NONE.

&&

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...Moreland