Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 212102
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
202 PM PDT Wed Jun 21 2017

...Excessive Heat Continues Across the Deserts Through the
Weekend...

.SYNOPSIS...
Very hot conditions will continue across the deserts this week
under a high pressure ridge. A shallow marine layer will continue
to moderate conditions along the coast and into the western
valleys, along with areas of nocturnal clouds and fog, lingering
into the afternoons at some beaches. It will be a little cooler
west of the mountains over the next couple of days as onshore
flow increases, extending the marine influence farther inland. The
foothills and lower coastal slopes will remain seasonably hot
through the weekend. Inland temperatures closer to seasonal
averages could return towards the middle of next week.

&&

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

Upper ridge will continue to be centered over Arizona through the
upcoming weekend. The strength of the ridge locally has been eased
a tad as a trough to our north skirts by. This pattern will lead
to slightly lower temps area wide along with a continued marine
influence along the coast. In fact, the marine layer will deepen a
tad over the next few days as inland pressure gradients increase.
This will allow more cooling to occur further inland into the
inland valley and to the mountain regions. However, the deserts
will remain excessively hot through the weekend, even despite a
lowering of temps by a few degrees.

There was a moist surge across the Coachella Valley today and this
has held temps lower compared to yesterday. As such, 120s may be
difficult to attain. Highs were lowered, though still excessively
hot well into the 110s this afternoon. 110s will continue across
the lower deserts through the weekend with the high desert into
the 105-110F degree range each day.

Winds again will increase later this evening across the desert
slopes and through the passes with gusts to near 30 mph
anticipated before lessening overnight. This pattern will repeat
itself the next few nights.

An upper-level disturbance moving westward on the south side of
the upper level high could bring some elevated moisture to SoCal
on Sat and Sun. This is unlikely to have much of an effect on
conditions since any associated clouds will be mostly thin and
above 10000 ft.

More noticeable cooling is possible for the middle of next week as
the upper ridge weakens in response to a low pressure trough
moving inland to our north.

&&

.AVIATION...
212100...Coast/Valleys...Clouds and fog along the coast will move
inland after 03Z. Bases around 600 feet msl with tops to 1100 feet.
Vis 3-5sm along coast, but locally 0-2sm especially in valleys and
coastal mesas between 12-15Z. Scatter out Thursday by 16-17Z, but
still not completely clearing at immediate coast.

Mountains/Deserts...P6SM vis and SKC through Thursday. High density
altitude at KPSP and KTRM with max temperatures 115-118.

&&

.MARINE...
A shallow marine layer will continue to bring patchy dense fog (with
visibilities of 1 NM or less) to the coastal waters through at least
Thursday morning. Confidence lower, but dense fog possible nights
and mornings through weekend.

&&

.BEACHES...
A southerly swell of 3-4 ft/13-15 seconds from 165-170 degrees
combined with a short-period westerly 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 Thursday.
This swell will also produce surf to 5 ft (with local sets to 6 ft)
at Orange county beaches and San Diego county beaches north of
Oceanside. Also, the aforementioned high tides will likely reach
around 7+ ft during the mid-evening hours Thursday through Saturday.
Tides this high may result in minor tidal overflow at low lying
beaches. The Beach Hazards Statement continues through Friday, and
may need to be extended into Saturday.

&&

.FIRE WEATHER...
The hot weather, coupled with very low relative humidity will
make it difficult to extinguish any wildfires that develop or are
ongoing in wind-prone areas for the next few days, but forecast
conditions remain generally below criteria for a Fire Weather
Watch or Warning.

Elevated Wildfire conditions will generally prevail along the
mtn/desert interfaces, where the combination of heat, gusty winds
and low relative humidity will exist. Of greatest concern will be
the ridges and north slope of the San Bernardino Mts, where
southwest winds of 15 to 20 MPH with gusts of 30 MPH or more, and
RH values of 10% or less are expected each afternoon/evening.

&&

.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 Sunday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

     Heat Advisory until 9 PM PDT this evening for Orange County
     Inland Areas-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.

PZ...NONE.
&&

$$

PUBLIC/FIRE WEATHER...Gregoria
AVIATION/MARINE...MM



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