Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 271633
Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Thu Apr 27 2017
Areas of low clouds this morning will gradually clear, with mostly
sunny skies this afternoon. Low clouds will just be patchy tonight
as areas of northeast winds develop below passes and canyons. The
winds will become locally strong Friday night and Saturday morning
but diminish rapidly Saturday afternoon. Otherwise, fair weather
will prevail through the middle of next week with temperatures
averaging a little above normal, except for a very warm day Saturday
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Low clouds covered San Diego County coastal areas and parts of the
Orange County coast at mid-moring, with some high clouds drifting
over the region. It may take until around noon for the stratus to
clear San Diego County, but overall fair weather will prevail today
with temperatures similar to those from Wednesday.
Broad low pressure aloft covered much of the contiguous US with a
high pressure ridge over the East Pacific. A shortwave moving
southeast from the Pacific Northwest will help amplify the interior
western US part of the trough while the upper high off the coast
also amplifies, and the resulting north flow aloft will combine with
a surface high moving into the Great Basin to produce increasing
offshore flow from tonight through Saturday morning. With a stable
layer between about 750 and 650 MB north of the San Bernardino
Mountains, there is a potential of a strong mountain wave which
could drive strong winds into the valleys. Gust potential is greater
than 60 MPH below Cajon Pass and in/just below the Santa Ana
Mountains. Will consider a high wind watch for Friday night/Saturday
morning for the afternoon forecast package for the Inland Empire and
Orange County. The marine layer should be wiped out for a while with
the offshore flow, and temperatures should increase west of the
mountains Friday and especially Saturday. Some highs in the 90s will
be possible Saturday in the valleys and even some areas 15 miles
inland from the coast. Onshore flow rapidly returns by Sunday, so it
will be cooler west of the mountains. The upper high over the East
Pacific could move into California early next week, but with onshore
flow, a marine layer will form beneath the subsidence of the high
and keep the coast cool with some stratus at times, while inland
areas will be quite warm, generally in the 90s in the lower deserts
and 80s in the valleys for highs.
271532Z...Coast/Valleys...BKN-OVC stratus about 10-25 sm inland with
bases 1200-1700 ft msl and tops around 2000 ft msl will clear to the
coastal waters through 1900 UTC. 1900-28/1500 UTC...primarily P6SM
vis and SCT-BKN clouds AOA 20000 ft msl, with possibly some patches
of BKN clouds 1000-2000 ft msl within 15-25 sm inland during the
28/0300-1500 UTC time-frame.
Mountains/Deserts...After 28/0000 UTC, W winds 15-25 kt with gusts
35-40 kt along mountain ridges, desert slopes and through the
passes, resulting in mod-strong uddfs/llws over and east of the
mountains. Vis briefly reduced in BLDU and sand in the deserts.
Otherwise, SCT-BKN cloud layers AOA 20000 ft MSL and P6SM vis
through Friday morning.
Northwest winds over the outer waters will continue to gust 25-30 kt
through late Friday night. In addition to the winds, short-period
seas will increase to 9-12 ft. A Small Craft Advisory for the outer
waters starts continues through late Friday night.
For the inner waters, outer portions of that zone may get 25 kt
gusts by late this afternoon, with more widespread strong winds
likely late Friday, along with steep seas. A Small Craft Advisory
for the inner waters starts 3 pm today and continues through late
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
PZ...Small Craft Advisory until 5 AM PDT Saturday for Waters from San
Mateo point to the Mexican Border Extending 30 to 60 nm out
including San Clemente Island.
Small Craft Advisory from 3 PM this afternoon to 5 AM PDT
Saturday for Coastal Waters from San Mateo Point to the
Mexican Border and out to 30 nm.