Wildfire in California, July 25 to 31, 2018

Area Forecast Discussion
National Weather Service San Diego CA
950 AM PDT Wed Jul 25 2018

.UPDATE...
A thick marine layer along the coast may keep some beaches cloudy
throughout the day today, which will also keep coastal locations
cooler. Surface dewpoint temperatures have increased to the low
70s in the lower deserts this morning. This will also likely
limit how high temperatures can get in the San Diego County
Deserts and the Coachella Valley this afternoon. The update this
morning lowered highs along the immediate coast, over the San
Diego Valleys, and for the lower deserts. The eddy is expected to
linger through Friday, which will help keep locations right near
the coast not as hot. The Climate section below has been updated
with the newest forecast high temperatures.

&&

.SYNOPSIS...
Strong high pressure aloft will continue our very hot weather
through Thursday except near the beaches and at the highest
elevations of the mountains. A weak coastal eddy will bring patchy
late night and early morning low clouds and fog near the coast. A
few thunderstorms may form over the mountains today. The high will
weaken slightly Friday through the weekend, but it will still be
hotter that average. Scattered thunderstorms are possible over the
mountains and deserts this weekend through early next week.

&&

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

.PREV DISCUSSION FROM 355 AM THIS MORNING...
Despite the synoptic scale subsidence associated with strong high
pressure aloft, there will still be a chance for afternoon
thunderstorms over the mountains today. PWATs will be around 1.2"
this afternoon, and like Tuesday, if parcels reach the LFC there
will be 500-1000 J/kg of energy for updrafts to grow into isolated
TCU.

Thursday will be another very hot day in the mountains and deserts
where highs will essentially be unchanged from today. That means
another day of highs near 120 in the Lower Deserts and near 110 in
the High Deserts. Coastal and valley highs may trend downward a
couple degrees as the high aloft weakens slightly and stronger
surface pressure gradients resulting in a stronger sea breeze.

For Friday the models are trending slower with the retreating upper
high over the Southwest and hotter with the daytime highs over the
lower deserts. MOS guidance for Max T at PSP and TRM Friday is above
115, and the Excessive Heat Warning may need to be extended to
Friday in the deserts. West of the mountains it will be a few
degrees lower than Thursday.

Over the weekend the high doesn't fully relent and temperatures will
still be above average for the end of July. It will still be hot,
just not quite as hot west of the mountains where the coastal eddy
and a deeper marine layer will spread inland. Valley highs will
range from 90-100, and coastal highs will be from 75 at the beaches
to around 90 ten miles inland.

The high lifts north Saturday and Sunday, and the ensuing weak
monsoonal east-southeast mid-level flow will bring a greater chance
for mountain and desert thunderstorms over the weekend through early
next week.

&&

.AVIATION...
251600Z...Coast/Valleys...Mostly clear with unrestricted
visibilities, except near the coast and locally inland BKN-OVC low
clouds based 700-1000 feet MSL with tops near 1200 feet MSL
and local visibilities 2-4 miles in fog and haze.

After 26/04Z low clouds and fog spreading onshore, extending inland
about 10-15 miles overnight. Local visibilities below 1 mile along
the inland edge of the low clouds. The risk of low clouds returning
again tonight is high, so high confidence in the KSAN TAF low cloud
forecasts.

Mountains/Deserts...Isolated SHRA/-TSRA possible over the mts in the
afternoon. CB bases near FL100 with tops to FL300. Otherwise...SCT
clouds AOA FL150 and unrestricted vis through tonight.

&&

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

&&

.Beaches...
Swells from the Southern Hemisphere at 16-17 seconds from 200
degrees will bring high surf through the day. The highest surf will
be on the south and southwest facing beaches of Orange and Northern
San Diego Counties today, where waves of 5-9 ft are likely. The surf
and swell will gradually lower Thursday. Strong rip and longshore
currents will create hazardous swimming conditions at all beaches. A
High Surf Advisory remains in effect through 9 PM Today.

&&

.FIRE WEATHER...
The extreme heat and low humidities will continue elevated fire
weather conditions through Thursday or Friday, especially in the
deserts and desert slopes of the mountains where westerly winds with
gusts to 35 MPH will occur each late afternoon and evening.

&&

.CLIMATE...
Possible record high temperatures for Wednesday based on the
forecast temperatures:

Location           Forecast      Current Record
Riverside            108          107 in 1943
Ramona               103          101 in 1977
Campo                107          104 in 1959
Thermal              116          115 in 2000
Borrego              116          115 in 2000

Possible record high temperatures for Thursday based on the
current forecast temperatures:

Location           Forecast      Current Record
Ramona               102          102 in 1977

San Diego, Santa Ana, Riverside, Palm Springs, Thermal, and Campo are
among the locations that are on track for 2018 to be among the 5 warmest
Julys on record. If that occurs for Santa Ana, Riverside, Palm Springs,
and Thermal, 6 of the 10 warmest Julys on record for those locations
will have occurred since 2005, with 5 of the 10 warmest Julys for Campo
since 2005, and 4 of the 10 warmest Julys for San Diego since 2005.

&&

.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 Thursday 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.

     Heat Advisory until 8 PM PDT Thursday for Orange County Coastal
     Areas-San Diego County Coastal Areas.

     High Surf Advisory until 9 PM PDT this evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.
&&

CLIMATE/UPDATE...JJT
PUBLIC/FIRE WEATHER...MOEDE
AVIATION/MARINE...Small