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Forecast Discussion for San Diego, CA

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FXUS66 KSGX 211148 AAA

Area Forecast Discussion
National Weather Service San Diego CA
450 AM PDT Sat Jul 21 2018

Monsoonal moisture will increase slightly today with a chance of
thunderstorms for this afternoon and early evening in the mountains
and high deserts. Strong high pressure aloft will move into the
southwest states for the early to middle part of next week bringing
a strong warming trend early next week with the heat expected to
peak on Tuesday and Wednesday. A shallow marine layer and weak
coastal eddy will keep areas near the coast not as hot with patchy
late night and early morning low clouds and fog near the coast.
Towards the end of next week into next weekend...the high pressure
will weaken slightly and shift northward slightly. This will bring a
cooling trend with some return of monsoonal moisture



.SHORT TERM (Today through Monday)...
Update to account for outflow from thunderstorms over Arizona that
may reach desert areas during the morning. The update to the winds
was based on the 10Z HRRR.  The details will probably change some in
subsequent runs. The current timing would have the outflow reaching
the southern end of the Coachella Valley after 8 AM.

In the local area...there was one isolated thunderstorm during
Friday afternoon to the southwest of the Barstow are where there
was sufficient lower level lift from the intersection of two
convergence boundaries...with those convergence boundaries well
forecast by the local higher resolution models.

Southeasterly flow between low pressure well off the Southern
California coast and high pressure over west Texas will bring a
slight increase in monsoonal moisture today. For this afternoon...
the local workstation WRF with NAM boundary conditions develops
some thunderstorms along convergence boundaries from the San
Bernardino Mountains northward into the high desert...and along
convergence boundaries on the east slopes of the mountains of
Riverside and San Diego Counties with that model showing hourly
rainfall to around one half inch with some of those cells. That
southeast flow will also spread some higher level moisture and
high clouds across the area today...some of which is from a
thunderstorm complex over Sonora and south central Arizona.

Otherwise...the forecast is little changed through Monday. The
marine layer will deepen slightly into Sunday with night and
morning coastal low clouds becoming a little more extensive and
spreading a little farther inland...into the western valleys at
times. For today...there will be some minor changes in high
temperatures from those of Friday. For Sunday and Monday...strong
high pressure aloft centered over New Mexico will move slowly
westward. This will bring slow warming on Sunday and greater
warming on Monday with well above average high temperatures inland
from the coast on Monday.


.LONG TERM (Tuesday through Saturday)...
Strong high pressure aloft will move over the southwest states for
the early to middle part of next week. This will bring a period of
very hot weather except near the coast and in the highest
elevations of the mountains. The heat is expected to peak on
Tuesday and Wednesday. Nights will be quite warm as well...especially
near the foothills of the mountains and in the deserts. Toward the
end of next week into next weekend...the high pressure may weaken
slightly and shift northward slightly. This would allow for some
cooling and some return of monsoonal moisture with continuing run
to run and model to model differences among the global models with
the evolution of the high pressure late next week into next


210815Z...Coast/Valleys...Stratus bases BKN-OVC012-016 tops 018
spreading 15 miles inland through 16Z. Local vis 2-4 miles in
fog/haze on higher terrain. Low clouds retreating back to the coast
and clearing from KSAN and KCRQ through 20Z. After 02Z...low clouds
BKN-OVC012-016 returning and spreading 15 miles inland through 15Z

Mountains/Deserts...SCT-BKN100 through 18Z. After 18Z...scattered
TSRA with CB bases 8000 ft and tops to 35000 ft with strong
up/downdrafts and local surface gusts over 35 knots.


No hazardous marine weather is expected through Wednesday.


Smallish surf today will build on Sunday as a long period southwest
swell builds into the Southern California coastal waters. This swell
will be the largest of the summer so far. It will continue to build
on Monday and then peak Tuesday and Wednesday when surf of 6-8 ft is
likely in Orange County and the northern half of San Diego County. A
High Surf Advisory will likely be needed for this event. The swell
begins to fade Thursday but the surf will still be above average.
The surf and swell will continue to fade Friday and Saturday.


Possible record high temperatures for next Tuesday based on the
current forecast temperatures:

Location           Forecast      Current Record
Chula Vista           81           81 in 2014
Ramona               104          103 in 2006
Alpine               103          103 in 2006
Idyllwild             96           96 in 2014
Thermal              118          117 in 2000

Possible record high temperatures for next Wednesday based on the
current forecast temperatures:

Location           Forecast      Current Record
El Cajon              99           99 in 2006
Ramona               104          101 in 1977
Thermal              117          115 in 2000
Borrego              115          115 in 2000

Several record warm low temperatures are likely as well...especially
on Tuesday night and Wednesday night.


Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


CA...Excessive Heat Warning from 10 AM Monday to 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

     Heat Advisory from 10 AM Monday to 8 PM PDT Thursday for Orange
     County Coastal Areas-San Diego County Coastal Areas.





Previous Forecast Discussions may be found at
NWS San Diego, CA (SGX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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