Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 292130

Area Forecast Discussion
National Weather Service San Diego CA
229 PM PDT Wed Mar 29 2017

High pressure aloft will drift east tonight. On Thursday a deep
trough moving across the Great Basin will bring strong and gusty
west winds to the mountains and deserts. Cooler Friday behind the
trough with winds shift to the northeast. High pressure rebuilding
over the region Saturday will bring sunny and warm this weekend.
Cooler early next week as another trough moves in from the



High pressure aloft brought sunny, warm weather Wednesday. Highs
were in the 80s in most areas west of the mountains. Mountain highs
in the 60s and 70s, and the lower deserts were in the lower 90s.
Records are a little out of reach today.

The ridge axis shifts east tonight and we will transition to a
progressively stronger onshore flow pattern Thursday. A deep upper
trough will move into NorCal tonight and then across the Great
Basin/California interior on Thursday. The core of the strongest
winds in SoCal will be Thursday afternoon through Thursday evening,
a relatively short duration onshore wind event. Pressure gradients
ramp up Thursday afternoon and peak Thursday evening with a 994 mb
surface low over southern Utah. Strong gradient winds over the high
deserts from 20-30 mph with gust to 50 mph+. Mountain waves are a
near certainty with an inversion near 700 mb. West winds will
surface down the eastern slopes and into the lower deserts, but the
magnitude of the wind is still in question. The WRF is strongest
with the winds, as usual, and support a low end Wind Warning. But
the Cansac and NAM3 are weaker and support a Wind Advisory. Either
way, there will be a 6-12 hour period of gusty west winds between
Noon-10 pm Thursday. Surface winds of 20-30 mph are likely with peak
gusts of 50-60 mph on the slopes and some parts of the desert floor.
Rotors are likely in the Coachella Valley. A High Wind Watch remain
in effect for most of the mountain and desert areas Thursday
afternoon in Thursday night.

The winds shift north and weaken Thursday night as the trough moves
over northern AZ, setting up a brief period of offshore flow through
midday Friday. The north-south alignment favors gusty winds in the
Cajon Pass, parts of the IE and the Santa Ana Mountains. The
northern part of the Coachella Valley will also see gust north
winds. The remainder of Riverside County and most of San Diego
County will not be experience strong winds.

An sizable coastal eddy will spin up over the coastal waters tonight
which could generate low clouds or fog in the coastal zones tomorrow

Weekend outlook: High pressure aloft fills in behind the trough with
fair warm weather Saturday and Sunday. Another trough will move
across the Great Basin Monday and Tuesday for minor cooling. This is
a weaker inside slider that the upcoming Thursday event, and the
winds won`t be as strong in the mtns and deserts.


292000Z...Coast and Valleys...SKC and light afternoon sea breezes
will prevail this afternoon. Predominantly FEW AOA 20,000 ft msl
tonight, though there is some potential for patchy fog or low
stratus with bases AOB 1,000 ft msl along the San Diego County coast
between 10 and 15Z Thursday. Some clearing is possible between 15
and 20Z Thursday, before SCT-BKN bases AOA 2000 ft msl return to
coastal areas after 20Z.

Mountains and Deserts...FEW AOA 20,000 ft msl and light winds will
prevail through 15Z Thursday. Westerly winds and mountain wave
activity will increase after 15Z, peaking around 00Z Friday. This
will create strong up/downdrafts and LLWS over the deserts and along
the desert slopes, especially between 21Z Thursday and 04Z Friday.
Impacts from LLWS and gusty winds are possible for KPSP and KTRM.


No hazardous marine weather is expected through Thursday morning.
The passage of a cold front will bring NW winds 15-25 kt and
increasing seas Thursday afternoon and Friday. Strongest winds will
likely be found 10 miles offshore and beyond Thursday evening.
Highest combined seas are anticipated overnight Thursday into
Friday, with 3-6 ft seas inside of 30 miles building to 7-10 ft near
and south of San Clemente Island. Winds and swell should decrease
over the weekend, before increasing again early next week.


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


CA...High Wind Watch from Thursday afternoon through late Thursday
     night for Apple and Lucerne Valleys-Coachella Valley-
     Riverside County Mountains-San Bernardino County Mountains-
     San Diego County Deserts-San Diego County Mountains-San
     Gorgonio Pass Near Banning.




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