Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 280324
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
824 PM PDT Thu Jul 27 2017

.SYNOPSIS...
Seasonal summer weather through Friday with high pressure over the
Southwest. Weak monsoonal flow returns over the weekend with
isolated thunderstorms over the mountains and deserts Saturday and
Sunday. The monsoonal pattern strengthens Monday and Tuesday with
greater thunderstorm coverage over the mountains. Some
thunderstorms may drift west of the mountains into the valleys.

&&

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

...Update...

No showers or thunderstorms developed today as a drier airmass was
in place. Just a few cumulus developed over the mountains. The PW
on the San Diego sounding this evening was only at 0.84". A
tranquil night is expected with marine layer stratus along
portions of the coast developing further and moving some 15-20
miles inland. Further inland the sky will remain clear.

The temp soared to 115F degrees at Palm Springs this afternoon.
However, heights do lower a tad on Friday and for this reason
decided to keep the 110F forecast for Friday. No significant changes
will be made to the forecast this evening. See previous
discussion below for further forecast details.

...Previous Discussion (Issued at 148 PM PDT Thu Jul 27 2017)...

For mid summer today is shaping up to be near normal for most
areas. The marine layer is pretty strong for this time of the year
but the much lower atmospheric moisture has helped to burn off
the morning clouds quicker than previous days. With the relatively
strong marine layer in place morning clouds will slow heating
near the coast Friday morning, but clearing will affect all areas
by late morning. Temperatures Friday will be similar to today.

A gradual return to a SE monsoonal flow pattern will setup this
weekend. On Saturday there will be a slight chance for mountain
thunderstorms in the afternoon and evening and with dry lower
levels there will be a slight risk for dry lightning strikes.
Sunday through next week will see gradual increase in atmospheric
moisture due to persistent SE flow in our region. Monday and
Tuesday may see the highest relative coverage of convection,
possibly affecting areas west of the mountains too, due to a
couple of weak easterly waves moving through the flow regime.
Flash flood risk will also be relatively the highest at that time
due to potentially better thunderstorm organization.

The moist SE monsoonal pattern will generally continue through
next week. Deep tropical moisture will remain well to the south as
the hurricane activity moves west over the open Pacific Ocean.

The medium range models are suggesting that a strong upper level
high will shift north across Central and Northern Nevada towards
the end of next week. The GFS is more aggressive strengthening the
high to 600 DM during the period which could bring a very hot
pattern to the deserts, with the most abnormally hot weather north
of our area...but continued above normal for Southern California
as well.

&&

.AVIATION...
280300Z...Coasts/Valleys...Through 28/1400 UTC, stratus moving
15-20 sm inland, with bases around 1200-1600 ft msl, tops around
1800-2000 ft msl and local vis 3-5 sm. Confidence in stratus/fog
reaching KONT is low. Forecast marine layer inversion strength of
6.5C at 28/0000 UTC. Clearing of stratus likely during the
28/1500-1800 UTC timeframe. For valley locations beyond 20 sm
inland, P6SM vis and mostly SKC will likely continue through
Friday morning. Low stratus will move back in after 29/0200Z near
the coast.

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

&&

.MARINE...
No hazardous marine weather is expected through Tuesday.

&&

.BEACHES...
Wave Watch 3 continues to show the upcoming swell generated by
Hurricane Hilary peaking at around 5 ft/13-15 seconds from 180-190
degrees late Saturday through late Monday. A reinforcing swell with
a longer period south swell (also from 180 degrees) will reach
around 2-3 ft/18-19 seconds Monday through Wednesday. These two
swells will likely combine to bring high surf of 5-7 FT with sets to
8 or 9 FT along south facing beaches of Orange county and Northern
San Diego county, mainly Saturday through Tuesday. A Beach Hazards
Statement remains in effect due to the potential for high surf. The
forecast surf heights could change depending on the track and
strength of Hilary, which is still somewhat uncertain. The swells
will also create strong rip and longshore currents, resulting in
dangerous swimming conditions.
&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Saturday morning through Tuesday
     evening for Orange County Coastal Areas-San Diego County
     Coastal Areas.

PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/Brotherton (Prev Discussion)
AVIATION/MARINE...Gregoria/PG



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