Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 300316
Area Forecast Discussion
National Weather Service San Diego CA
816 PM PDT THU SEP 29 2016
Warm weather will continue over the next couple of days with
daytime high temperatures in the 80s and 90s across the inland
valleys. Temperatures will steadily decrease through the weekend
into early next week. Onshore flow will strengthen with a return
of the marine layer. Gusty winds will develop over the mountains
and deserts each afternoon and evening beginning Saturday,
strongest on Sunday and Monday. Monday will also likely be the
coolest day, with daytime high temperatures mostly in the 70s west
of the mountains. A warming trend begins Tuesday and continues
through the work-week.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Residual low and mid-level moisture coupled with daytime heating
resulted in widespread cumulus clouds across the region this
afternoon. An upper level disturbance moving northeast provided
enough dynamic forcing to trigger sct tstms over the mtns in
southern San Diego County. The storms resulted in significant,
localized rainfall. One location recorded 0.78 inches in less than
one hour. The upper level disturbance is moving northeast and the
convection has dissipated, leaving behind significant amounts of
low and mid-level debris clouds.
A vigorous, large-scale trough of low pressure now off the coast
of WA/OR will intensify and move southeast through the weekend. A
closed upper low will reach southern NV/CA by Monday morning. This
will bring a significant cooling trend, with daytime high
temperatures lowering into the 70s west of the mtns, even in the
inland valleys. This low pressure trough will also bring a return
of coastal low clouds and strong onshore flow. The onshore winds
will peak Sun night/Mon morning, producing wind gusts of 40-60 mph
at times in the mtns and adjacent desert areas. Current model
solutions are mostly dry for our region but the ECM does show some
small amounts of precip on Mon morning, in contrast to the GFS
which keeps all of the precip to our north. However, the marine
layer will be quite deep by then so some drizzle west of the
mountains will be possible.
Temperatures will begin to rebound for Tue through the end of the
work-week as high pressure aloft and possible offshore flow
develop as the trough moves east into the Rockies and Central
300305Z...Coastal and Valley areas...a few scattered high and mid
level clouds through 300600Z After 06Z...there is a risk of SCT-
BKN001-005 spreading 5-10 miles inland through 301600Z Friday. The
latest model runs are looking LESS likely that this will occur.
There also arisk of areas of vis 1-4 miles in fog from the coast
to the coastal mesas including KCRQ. Very low confidence of
lengthy impact at coastal airports. Clearing skies after 301600Z.
Friday night after 010200Z low clouds, fog with lower visibility
is really a major concern as the marine moisture moves inland with
stronger onshore flow as the next storm system moves in from the
northwest. Ceiling heights will start out likely below 200 feet
and visibility could be as low as 1-3 miles and could start as
soon as 010200Z. Confidence on Friday night into Saturday is
Mountains and Deserts...Clear skies and unrestricted visibilities
will be the general rule into Saturday. Tonight there are a few
clouds over the mountains with bases to 8000-12000 feet and
more will be likely Friday afternoon, but clear overnight.
High confidence forecast.
No hazardous marine weather is expected through Friday. Northwest
winds will increase over the weekend, strongest from Sunday
afternoon through Monday when winds over the Outer Waters will
increase to 20-30 kt. A Small Craft Advisory may be needed Sunday
and Monday for the combination of strong winds and high seas.
Prevailing southerly swells through Sunday will bring 3-5 foot surf,
with occasional sets to 6 feet in Orange County. High rip current
Strong gusty west winds may impact the beaches Sunday evening
through Monday afternoon as a deep Pacific trough moves inland.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.