Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 291640
AFDSGX

AREA FORECAST DISCUSSION
National Weather Service San Diego CA
940 AM PDT FRI JUL 29 2016

.SYNOPSIS...
A strong ridge of high pressure aloft will bring very warm
conditions for inland areas today. Monsoonal moisture will produce
increasing chances and coverage of afternoon and early evening
heavy showers and thunderstorms over the mountains and deserts
through Tuesday. Some cooling expected this weekend as the ridge
weakens slightly, then perhaps some warming Monday and Tuesday due
to slightly stronger high pressure. The ridge will then weaken
again Wednesday through the rest of the week as a trough of low
pressure moves in along the west coast, resulting in slow cooling.
Chances for afternoon and early evening thunderstorms decrease
starting Wednesday due to drier air moving in. Patchy night and
morning marine layer low clouds and fog will continue to be
possible over the coast and western valleys.

&&

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

Morning visible satellite shows that marine layer stratus is quite
patchy once again over the coast and coastal waters. The 12Z
Miramar sounding shows a precipitable water value of 1.34 inches
which is almost exactly what it was yesterday. One thing of note
is a capping inversion at 430 mb/23000 ft, which may inhibit the
vertical development of clouds this afternoon and early evening.
Nevertheless, the latest HRRR shows a few showers and
thunderstorms developing over the mountains and high deserts this
afternoon and early evening, with the best chances over San
Bernardino county. As far as temperatures go, although the ridge
aloft is forecast to weaken slightly, models show 850 mb
temperatures remaining about the same today, and so we could see
highs similar to what we saw yesterday, with temperatures 5-10
degrees above normal. Meanwhile, with the marine layer stratus
having been so patchy the past couple nights and the weather
pattern not changing significantly, am expecting any stratus along
the coast tonight and Saturday morning to be patchy once again.

Water vapor satellite shows a strong upper level ridge over the
desert southwest. Models show the ridge weakening through the
weekend which should bring some cooling. Then the ridge rebuilds a
bit Monday and Tuesday which could create slightly warming,
before a slow and gradual cooling trend begins again Wednesday
through the rest of the week as a trough moves in along the west
coast and the ridge aloft weakens. Models also show monsoonal
moisture increasing from the east to southeast direction through
next Tuesday, with precipitable water reaching 1.4 inches
Saturday, 1.7 inches Sunday and Monday, and 1.8 inches Tuesday.
This moisture, in addition to instability produced by day-time
heating, will result in chances for afternoon and early evening
heavy showers and thunderstorms over the mountains and deserts
through at least Tuesday. Storm motion looks light on Saturday and
Sunday, which would increase the flash flood threat, especially on
Sunday when more low level moisture moves in.

Although moisture starts to decrease Wednesday into Thursday,
wouldn`t be surprised if there was still enough moisture and
instability to create isolated afternoon/early evening showers
and thunderstorms over the mountains on those days. Meanwhile,
onshore flow will continue to result in patchy night and morning
stratus/fog over the coast and western valleys.

&&

.AVIATION...
291500Z...Coast and Valleys...P6SM and SKC-FEW100-150, except for
patchy stratus development late tonight between 30/10-16Z over the
coastal waters, extending inland up to 10-15 miles with bases 800-
1200 FT MSL and tops AOB 1500 FT MSL. Local vis restrictions of 1-3
SM possible along the higher coastal terrain.

Mountains and Deserts...P6SM and FEW-SCT100-150 through this
evening, except for possible isolated thunderstorm development 20Z-
02Z along the ridge tops and across the high desert with assoc UDDFS
and LLWS.

&&

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

&&

.FIRE WEATHER...
With mid-level moisture and instability, some afternoon and early
evening thunderstorms are likely to develop over the mountains
and portions of the deserts through at least Tuesday. The
thunderstorms may initially produce dry lightning strikes today
and Saturday, and then becoming mainly wet strikes by Sunday.

&&

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

&&

.SGX Watches/Warnings/Advisories...
CA...None.
PZ...None.
&&

$$

PUBLIC/FIRE WEATHER...Harrison
AVIATION/MARINE...TS


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