Scientific Forecaster Discussion
fxus66 ksgx 271614
Area forecast discussion
National Weather Service San Diego California
914 am PDT Tue Jun 27 2017
stronger onshore flow will bring a cooling trend through Thursday
with high temperatures returning to near average for Wednesday and
Thursday. Coastal low clouds and fog will return to coastal areas
tonight...and spread into some valleys late tonight into Thursday
morning. Slightly warmer Friday under weak high pressure...then
slow cooling for Saturday through early next week with a weak
trough of low pressure across Southern California.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Much like yesterday there was exactly one patch of fog along the
San Diego coast from Cardiff south, but today we don't have a
southerly surge for that fog to move north along the coast. In
general, the clear sky above the ocean the past couple days was
probably the result of northwest flow just above the surface.
Now we watch a big tongue of stratus clouds marching swiftly and
purposefully into the bight. This appears to be in response to a
shortwave moving by to our north. The resulting decrease in high
pressure aloft will help the intense heat take a chill pill in
the interior away from the marine layer, and the marine layer
itself will take care of the cooling west of the mountains. Expect
more coastal clouds for the coming week. Initially this evening
the coastal clouds will be fog, but the cloud deck rushing into
our region is not as shallow on the deck as our coastal patch was
this morning. In other words, a whole different cloud in a shiny
new marine layer driving into the showroom. As it moves ashore
this evening it should deepen rapidly overnight to lift the fog at
the coast, but spread it inland into western valleys.
Temperatures, already running lower this morning, will trend
toward seasonal averages today and Thursday. A brief rebound in
the high pressure ridge appears on Friday before a weak trough
pattern arrives Saturday and continues into early next week. That
would temporarily make Friday a warmer day before getting back to
seasonal this weekend. The coastal clouds will make it into some
of the westernmost inland valleys during the nights.
271530z...coast...patchy fog along the immediate coast of San Diego
County is unlikely to impact any of the coastal taf sites. It should
mostly dissipate by 17z but could linger at a few beaches into the
afternoon. More widespread low clouds are likely to develop along
the coast between 03z-06z Wed with bases near 500 ft mean sea level. Low clouds
will slowly spread 10-15 miles inland by 12z Wednesday morning, with
bases 500-800 ft mean sea level. Expect areas of fog with vis 3-5 sm. Vis may
be reduced locally to 1sm or less on the coastal mesas and over
higher coastal terrain. Otherwise, clear with unrestricted vis
through Wed morning.
Valleys/mountains/deserts...except for smoke near San Gorgonio Pass
and aloft vicinity kpsp, clear skies with unrestricted vis will prevail
through Wed morning. West winds gusting 30-40 kt will occur over and
east of the mountains through tonight. This will produce low level wind shear and
MDT up/downdrafts over and east of the mountains through Tuesday
evening. Winds will weaken early Wed morning.
stronger west northwest winds with local gusts 20-25 kt will develop
this evening near San Clemente Island. Areas of fog with
visibilities 1 mile or less are likely late tonight into Wednesday
morning. Otherwise, no hazardous marine conditions are expected
single-digit humidity will continue for the deserts and desert
slopes of the mountains of Riverside and San Diego counties
through Wednesday with a slight recovery Thursday. Stronger
onshore flow will bring periods of strong gusty west winds along
the desert slopes of the mountains into the deserts of Riverside
and San Diego counties through late tonight. Critical fire weather
conditions will continue through Wednesday night, however they
will become more localized and mostly in the desert where there is
little if any fuel to burn if a fire were to start. The red flag
warning remains in effect through 1 am Wednesday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...red flag warning until 1 am PDT Wednesday for Coachella Valley-
including the Palm Springs South Coast desert district-
Riverside County mountains-including the San Jacinto Ranger
district of the San Bernardino National Forest-San Diego
County deserts-including the Anza Borrego Desert State Park-
San Diego County mountains-including the Palomar and
Descanso Ranger districts of the Cleveland National Forest-
San Gorgonio Pass near Banning.