Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 220350

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

...Excessive Heat in the Deserts through the Weekend...

Continued hot in the deserts through Sunday under high pressure
aloft. It will not be quite as hot in the valleys the next couple
of days as onshore flow increases, extending the marine influence
farther inland. The marine layer will continue to moderate
temperatures in the coastal zones with clouds lingering
into the afternoons at some of the beaches.  The mountains
will remain seasonally hot through the weekend.



Desert temperatures didn`t quite reach yesterdays levels, but 118
at Palm Springs, 116 at Ocotillo Wells, and 114 at Thermal is
plenty hot. Hesperia reached 103 today, two degrees lower than
yesterday. Meanwhile, 70 miles to the west the high was 65 in Del
Mar where clouds shrouded the beaches all afternoon.

High pressure over AZ is forecast to weaken slightly as a trough
passes by to north. This pattern will lead to slightly lower
temperatures, most noticeable in the Inland Empire where a greater
marine layer influence will keep highs from 90-100 Thursday and
Friday, instead of highs from 100-109 today. The deserts will remain
excessively hot through the weekend, with highs around 102-107 in
the high deserts and from 113-118 in the lower deserts. The Heat
Advisories will be allowed to expire at 9 pm for the valleys and

*From Previous Discussion*

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.


220300...Coast/Valleys...Stratus, with bases 300-700 ft MSL and
top to 1000 ft MSL, will continue to slowly develop inland around
10 miles by late tonight. VIS will drop to 2-4 SM BR near sea-
level, to as low as 1/2SM FG along higher mesas. Clouds will clear
towards the coast by mid Thursday morning where they will likely
linger again along the beach throughout the day.

Mountains/Deserts...P6SM vis and SKC through Thursday. High density
altitude at KPSP and KTRM with max temperatures 114-116.


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


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 6.5-7.5 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) along Orange county beaches and San Diego county
beaches north of Oceanside. Also, the aforementioned high tides
will likely peak 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.


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


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.



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