FXUS66 KSGX 290938
Area Forecast Discussion
National Weather Service San Diego CA
238 AM PDT Fri May 29 2020
High pressure over Southern California will weaken through Saturday
as a low pressure system moves northeast offshore. This will bring
stronger onshore flow and cooling, along with greater coverage of
low clouds into the valleys. The gusty south winds and hot, dry
weather over the high desert areas this afternoon will create a
period of elevated fire weather conditions. Another low pressure
area will form off the coast of Southern California early next week.
The proximity of this system will dictate how much of a change we
see in our Spring weather pattern, but expect some coastal low
clouds to persist, along with seasonally warm conditions inland. A
longer-period, south swell will create large surf and dangerous rip
currents at some beaches this weekend.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Low clouds were extensive overnight offshore and extended deep into
the valleys early this morning. Above this stratus layer were higher
clouds circulating around a cut-off low pressure center some 600
miles west of San Diego. Surface pressure gradients were weak to
moderate onshore this morning to the deserts, and at 2 AM PDT, only
light winds were reported.
For today the onshore gradient will be increasing to the high desert
areas as the cut-off low off the coast approaches. Southerly winds
will be rather strong and gusty off the San Bernardino Mts into he
high deserts by afternoon. Given the wind potential later today and
this evening, coupled with the heat and low relative humidity, a
Wind Advisory has been issued, mainly to highlight an elevated fire
The low pressure center will continue NE through Saturday,
maintaining onshore flow and a fairly deep marine layer west of the
mts. Clearing the stratus layer west of the mountains looks to be a
challenge today, but prospects are better on Saturday, except
perhaps along the immediate coast. Above the stratus and inland,
there will be some high clouds, but fair conditions will prevail,
with continued cooling through Saturday.
Sunday and early next week we will indicate some warming inland, but
continued onshore flow with a shallow marine layer over coastal
areas as a new upper low develops offshore. There is considerable
uncertainty regarding how far offshore this low will set up. For
now, the NBM solution was used to populate the maximum temp grids
beyond Monday. This solution is not as hot as it has been inland,
and a continuation of moderate conditions over coastal areas.
290830Z...Coast/Valleys...OVC skies with CIGS 900-1500 ft MSL and
tops to 2300 ft MSL will continue through at least 16Z at terminals
west of the mountains. Slow clearing toward the coast is likely
through 19Z, with coastal terminals including KSAN experiencing
limited if any clearing tomorrow. BKN skies may prevail for much of
the day, with cloud bases closer to 2000 ft MSL. Expect some VIS
restrictions of 3-5 miles on elevated terrain obscured in clouds.
Low clouds will expand inland again after 02Z Saturday with similar
bases and vis restrictions, affecting all valleys west of the
Mountains/Deserts...Skies will remain mostly clear through Saturday
with the exception of a few high clouds. Primary concern will be the
development of gusty winds Friday afternoon and evening from the
mountain crests north and eastward into the deserts. Surface gusts
of 25-35 kts will be possible at times, with LLWS and MOD-STG
up/down drafts probable over and east of the mountains. Strongest
winds are expected across the High Desert, through passes, and on
desert-facing mountain slopes.
Northwest winds gusting to around 20 kts, strongest over the outer
waters, are likely each evening through Monday.
A long-period south-southwest swell will generate elevated surf of 4
to 6 feet at area beaches through the weekend, with highest surf
conditions likely affecting south and southwest-facing beaches of
Orange County. Rip current risk will be high. A Beach Hazards
Statement is in effect for Orange County beaches - see the bulletin
for more information.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Excessive Heat Warning until 7 PM PDT this evening for Apple and
Lucerne Valleys-Coachella Valley-San Diego County Deserts-
San Gorgonio Pass Near Banning.
Wind Advisory from 2 PM this afternoon to 9 PM PDT this evening
for Apple and Lucerne Valleys.
Beach Hazards Statement from noon PDT today through Sunday
afternoon for Orange County Coastal Areas.
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