Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 232023
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
123 PM PDT Sun Apr 23 2017

.SYNOPSIS...
Increasing onshore flow through Monday will bring cooling well
inland, more nocturnal low clouds and fog as the marine layer
builds, and strong westerly winds across the mountains and deserts.
Fair, dry, and a little warmer midweek as the marine layer shrinks
and onshore flow weakens. Then, windy and cooler again Thursday and
Friday as a strong low pressure center develops over the Great
Basin. Fair, with a warming trend next weekend as the wind lets
up and high pressure rebuilds aloft.

&&

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

Satellite imagery midday showed the thicker high clouds had cleared
the forecast area, with patchy low clouds over the coastal waters.
Despite the strong April sun, temperatures at noon were running some
9 to 15 degrees F below values observed at noon yesterday. Westerly
winds were stronger too, with peak gusts of 35 to 45 MPH reported at
a few remote wind-prone sites in the mts. Surface pressure gradients
continue to gain momentum at 6-7 MBS onshore KSAN to the deserts.

Near term...The main weather concern over the next couple of days is
wind. Westerly winds are increasing today and will be quite gusty
over the mts/deserts this evening. A few gusts to 50 mph or more are
possible in wind-prone mtn and desert foothill areas. Even stronger
winds will develop late Mon through Mon night and should easily
reach Advisory strength over the mts/deserts at times. Local high
wind conditions are possible on the remote desert slopes Mon night
into early Tue where peak gusts could exceed 65 MPH. Expect a Wind
Advisory to be issued for these areas within 24 hours.

It will be cooler Mon with more morning marine clouds, but max temps
will still be within a few degrees of average, then warmer into Thu.

The pattern...
Strong high pressure aloft, centered over the EastPac along 135W,
and a broad trough over the Rockies and Great Plains will continue
a NW flow aloft along the West Coast this week. Shortwaves embedded
in that flow will bring periods of enhanced westerly winds across
SoCal, strongest over the mts/deserts and outer coastal waters late
Mon, and possibly again late in the week.

The latest GFS/ECMWF runs are coalescing around a solution that
strongly digs the Rockies trough on Fri/Sat, cutting off a low
pressure center over northern AZ on Sat. The GFS runs remain the
most aggressive. Depending on how this plays out, we will see more
strong onshore wind later this week, becoming northerly behind a
cold front at some point late Fri into Sat. Besides a period of
strong winds over the deserts/mts, it would be a little cooler than
previously forecast inland late in the week. Any cold advection
west of the mts would be mitigated by the downsloping, offshore
flow. Nights should be cooler though, with drier, continental air in
place and no cloud cover.

&&

.AVIATION...
232016Z...Coast/Valleys...Through 24/0000 UTC, primarily P6SM vis
and SCT-BKN clouds AOA 20000 ft msl. 24/0000-1600 UTC, BKN-OVC
stratus re-developing and gradually filling the coast and valley
areas, with bases 1500-2000 ft msl and tops near 2500 ft msl. Expect
areas of vis 3-5 sm in the valleys. Clearing of stratus likely
24/1600-1800 UTC.

Mountains/Deserts...West winds with sfc gusts 25-35 kt developing
along the ridges, desert slopes, through the San Gorgonio Pass, and
locally on the desert floor, with mod-stg UDDFS and pockets of LLWS
possible over/east of the mountains.

&&

.MARINE...
Periods of northwest wind gusts of 25-30 kt and combined seas of 10-
12 ft are possible in the outer coastal waters Monday evening
through Friday evening. This would result in conditions hazardous to
small craft through much of the week in the outer waters.

Meanwhile for the inner waters, gusts of 20 kt and seas near 8 to 9
feet will be possible at times, but Small Craft Advisory conditions
are not anticipated at the moment.

&&

.BEACHES...
A southwest swell from 200 degrees at 3 ft/15 seconds combined with
elevated west swells will produce surf of 3-6 ft with occasional 7
ft sets today and Monday. The above normal surf will also create
favorable conditions for strong rip currents and longshore currents.
A Beach Hazards Statement remains in effect through Monday evening.

A series of large short to moderate period northwest swells will
maintain elevated to locally high surf and strong rip currents
through most of the week.

&&

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

&&

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

PZ...None.

&&

$$

PUBLIC...JAD
AVIATION/MARINE/BEACHES...Harrison



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