Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 162052

Area Forecast Discussion
National Weather Service San Diego CA
152 PM PDT Fri Jun 16 2017

Strong upper-level high pressure building over the Southwest will
create hot to very hot weather inland through next week, with
Tuesday and Wednesday likely the hottest days. A shallow marine
layer will keep coastal areas cooler through the period, with
areas of night and morning low clouds and fog. Otherwise, skies
will be mostly clear.



The weather pattern through next week will be dominated by a
strong ridge aloft. Water vapor satellite shows the ridge to the
south starting to build into the region, bringing 590 dm 500 mb
heights. The 12Z Miramar sounding shows a few degrees of warming
taking place from the surface through most of the atmospheric
profile compared to yesterday`s 12Z sounding. This indicates the
anticipated warming and presence of the ridge taking shape. As of
1 pm, temperatures are several degrees higher than 24 hours ago.
Expecting highs today in the low 110s in the lower deserts, upper
90s/100 in the Inland Empire and High Deserts, upper 80s/low 90s
in the San Diego county valleys, inland Orange county and the
foothills of the mountains, 70s/low 80s at the coast and in the
higher elevations. This morning`s sounding also shows a marine
layer inversion of around 8 deg C at around 700-800 feet msl, and
areas of dense fog were reported within 3 to 8 miles of the
coast. Fog was able to clear by mid-morning, and visible satellite
shows clear skies across the region this afternoon.

The ridge will remain at around 591 dm 500 mb heights on Saturday
with little change in temperature. Although the ridge remains at a
similar strength Sunday, models show 850 mb temperatures
increasing a bit, so Sunday will likely be a bit warmer. The ridge
then strengthens next Monday and Tuesday, with 500 mb heights
reaching near 597 dm over us on Tuesday. Thus, expect significant
warming Monday and further warming on Tuesday. Although the ridge
appears to be strongest on Tuesday, 850 mb temperatures are
actually the highest on Wednesday, with the GFS and ECMWF showing
widespread 31 deg C all the way to the coast. So, wouldn`t be
surprised if Wednesday ends up being the hottest day of the heat
wave. The ridge weakens by a couple dm on Thursday, which should
result in temperatures about 5 degrees lower than Wednesday,
although it will still be hot, especially in the deserts. With the
position of the ridge moving more to the south over the SE
Arizona/SW New Mexico/Mexico border by Thursday, southerly flow
may bring enough moisture into the area for some cumulus build-ups
during the afternoon and perhaps a shower or two over the
mountains. This moisture could also serve to lower temperatures a
bit more than expected, but confidence in that occurring is low at
the moment. With the marine layer remaining very shallow due to
the ridge, dense fog will be possible along the coast each night
and morning, including tonight/Saturday morning. The presence of
the marine layer and onshore flow should keep temperatures at the
coast moderated.

For next weekend, GFS and ECMWF really don`t show the ridge going
away altogether. In fact, the ECMWF re-strengthens the ridge late
next Sunday, meaning that the heat wave may continue all the way
through next weekend!


162100Z...Coast... P6SM and mainly light winds through about 08Z
Saturday morning. Patchy low clouds/fog should return between 08Z
and 16Z Saturday with Ceilings mainly along the coastal strip with
bases 200-500 ft MSL and patchy dense fog and visibility down to 1/4
SM at times.

Valleys/Mountains/Deserts...SKC, P6SM and mainly light winds will
continue through 00Z Sunday.


Areas of dense fog possible with visibilities 1 NM or less over the
coastal waters, primarily during the overnight and morning hours,
through the middle of next week. Otherwise, no hazardous marine
weather is anticipated, with seas running 4 ft or less and mainly
light northwest winds.


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


CA...Excessive Heat Warning until 9 PM PDT Wednesday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near

     Heat Advisory from 11 AM Saturday to 9 PM PDT Wednesday for
     Riverside County Mountains-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Mountains.

     Excessive Heat Warning from 11 AM Saturday to 9 PM PDT Wednesday
     for Apple and Lucerne Valleys.

     Heat Advisory from 11 AM Monday to 9 PM PDT Wednesday for Orange
     County Inland Areas-San Diego County Valleys-Santa Ana
     Mountains and Foothills.




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