Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 222232
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
332 PM PDT Thu Jun 22 2017

.SYNOPSIS...
Southern California weather will continue to be dominated by a
ridge of high pressure. The center of the ridge will lie over
southern Arizona through the weekend and actually re-strengthen
over the local area this weekend. This will continue excessive
heat across the deserts through the weekend and even into Monday
for the lower deserts. It will continue to be slightly cooler
west of the mountains through Friday before conditions heat back
up over the weekend inland from the coast, especially Sunday. The
immediate coast will continue cool due to the continued influence
of the marine layer. The ridge of high pressure will gradually
become displaced south over northwestern Mexico and the adjacent
Pacific next week, leading to gradual cooling area wide.

&&

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

.Highlights...

* Excessive Heat Lower Deserts Through Monday; High Deserts
  Through Sunday

* Heat Advisory Issued for the Inland Empire, Mountains Below 5000
  Feet Including the Santa Ana Foothills, and Inland San Diego
  County Effective on Sunday

A hot ridge of high pressure will continue to dominate the
weather across Southern California through the weekend. The
strength of the ridge has lessened and continues to be situated
over Arizona. However, model consensus shows the ridge
re-strengthening across the area this weekend. In fact, H85 temps
climb to near what occurred this past Tue-Wed. This will lead to
an increase in temperatures with perhaps another shot at 120F
degrees across the lower deserts by Sunday. This long duration
desert heat wave continues.

Model trends continue to show increasing temperatures away from
the coast this weekend, especially Sunday and possibly even
Monday. The marine layer will gradually become shallower by the
weekend as the ridge re-asserts itself. H5 heights are climbing in
the models, now showing 595-596DM into our service area this
weekend, even through Monday per GFS. This will lead to hotter
temps for areas inland from the coast.

Given the ridge strength projected and model trends, decided to
issue a Heat Advisory for the Inland Empire, the mountains below
5000 feet, and Inland San Diego County effective Sunday. This
looks to be the hottest day of this secondary heat peak. We will
have to monitor to see if this needs extension into Monday as
well, but wanted to get the word out on the heat for these areas,
especially since the trend continues to increase. Saturday was
not included as most locales do not meet heat advisory conditions,
though isolated locales could. Sunday is the hot one (high enough
confidence on an advisory) and perhaps Monday, so this advisory
could need extension into Monday.

Early next week the ridge will finally become displaced over
northern Mexico and the adjacent Pacific. This will lead to zonal
flow with gradually lowering heights and a gradual cooling trend
from Tuesday on.

Models continue to show an upper wave rotating around the ridge
periphery Fri-Sat, but this looks to bring just a bit of high
level moisture with perhaps some high level cloudiness. There is
some limited instability aloft, but the assessment is that it is
not enough to produce dry lightning. Aside from patchy drizzle
along the coast tonight, have a dry forecast through the period.

&&

.AVIATION...
222012...Coast/Valleys...Through 23/0000 UTC, mostly P6SM vis and
SKC, except at and near portions of the beaches where BKN-SCT
stratus clouds around 1000-2000 ft msl and 5 sm vis may linger.
23/0000-1600 UTC, low stratus re-developing 15-25 sm inland, with
bases around 400-800 ft msl, tops around 1500-2000 ft msl, areas of
vis 1-5 sm and local vis down to 1/4 sm. Moderate confidence that
KONT and KSBD will get some low clouds/fog by 23/1400 UTC. Clearing
of stratus/fog taking place 23/1600-1900 UTC.

Mountains/Deserts...P6SM vis and mostly SKC through Friday morning.

&&

.Fire Weather...

Winds peaked to 33 mph across the San Bernardino desert slopes
into the high desert (through and downwind of the Cajon Pass),
except to 43 mph at Burns Canyon. Similar winds are expected
across these areas late this afternoon and early this evening
with a few hours of gusts to around 35 mph. These gusty winds
combined with the low relative humidity (5-15%) will create a few
hours of conditions favorable for quick spreading wildfires.
However, a Red Flag Warning will not be issued as conditions are
borderline and of short duration. Winds Friday afternoon-evening
will be less with gusts 25-30 mph forecast.

Some upper level moisture and limited instability will move into
the area on Saturday. The moisture and instability combo looks
limited enough to where we did not include dry lightning in the
forecast. Chances are too low, but something we will monitor.

&&

.MARINE...
A shallow marine layer will continue to bring patchy dense fog (with
visibilities of 1 NM or less) to the coastal waters this morning.
Patchy dense fog will be possible during the nights and mornings
through the weekend.

Northwest wind gusts over the outer waters may reach 25 kt during
the afternoons and evenings from Sunday through Tuesday, potentially
resulting in conditions hazardous to small craft.

&&

.BEACHES...
A south swell of 3-4 ft at 13-15 seconds from 165-170 degrees
combined with a short-period west swell and large tidal swings (high
tides of 6.5-7 ft with low tides around -1.0 ft), will result in
strong and dangerous rip and longshore currents through Friday. This
swell will also produce surf to 3-6 ft (with local sets to 7 ft) at
Orange county beaches and San Diego county beaches north of
Oceanside. Also, the high tides will likely reach around 7+ ft
during the evenings today through Saturday. Tides this high may
result in minor tidal overflow at low lying beaches. The Beach
Hazards Statement has been extended through late Saturday evening.
The high tides will fall below 7 feet Sunday, lowering the tidal
overflow threat.

&&

.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 9 PM PDT Monday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

     Heat Advisory from 10 AM to 9 PM PDT Sunday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-San Diego County Valleys-Santa Ana
     Mountains and Foothills.

     Excessive Heat Warning until 9 PM PDT Sunday for Apple and
     Lucerne Valleys.

PZ...NONE.
&&

$$

PUBLIC...Gregoria
AVIATION/MARINE...Harrison



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