Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 272056
Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Thu Apr 27 2017
High clouds will continue to move through the region this afternoon
and tonight. Low clouds will just be patchy tonight as areas of
northeast winds develop below passes and canyons. The winds will
become strong Friday night and Saturday morning, especially in the
Inland Empire and Orange County, 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
Patchy low clouds continued over San Diego County coastal areas this
afternoon, with high clouds covering most of So-Cal. Due to the
marine layer, temperatures were a little cooler west of the
mountains today, with mostly just 70s in the valleys, but a few
locations in the lower deserts topped 90. Local wind gusts were over
30 MPH in the mountains and deserts, and some gusts around/over 40
MPH will occur this evening before winds switch more north/northeast
in the mountains.
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 a little above
90 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, though the mountains and
especially the deserts will be warmer due to increasing temps aloft.
The upper high over the East Pacific will shift 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 to around 100 in the lower deserts and 80s to lower 90s
in the valleys for highs through at least Thursday.
272002Z...Coast/Valleys...patches of BKN-SCT stratus within about 15
sm inland with bases 1200-1700 ft msl and tops around 2000 ft msl
will clear to the coastal waters through 2200 UTC. 2200-28/1500
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 strengthen again this
afternoon with gusts 25-30 kt likely this evening 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.
CA...High Wind Watch from Friday evening through Saturday afternoon
for Orange County Inland Areas-San Bernardino County
Mountains-San Bernardino and Riverside County Valleys-The
Inland Empire-Santa Ana Mountains and Foothills.
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 until 5 AM PDT Saturday for Coastal Waters
from San Mateo Point to the Mexican Border and out to 30 nm.