Scientific Forecaster Discussion
fxus66 ksgx 270357
Area forecast discussion
National Weather Service San Diego California
857 PM PDT Mon Jun 26 2017
the weather will not be as hot for the coming week as high pressure
aloft relaxes and the marine layer rebuilds. Locally strong westerly
winds will push through mountain passes and into deserts during
afternoons and evenings. The marine clouds and fog will return and
gradually spread into the valleys in the coming nights.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
The sky was clear across the socal at 8 PM PDT. Winds were
increasing across the mountains and deserts with onshore sfc
pressure gradients to the deserts increasing. The 00z Miramar
sounding had a weak inversion based near 1300 feet mean sea level with increasing
northwest flow from the sfc t0 approximately 10k feet. Peak wind gusts
exceeding 60 miles per hour were observed at Burns Canyon near the morongo pass
area in the San Bernardino mts late today, with numerous other
sites across the High Desert recording peak gusts in excess of 35
miles per hour. The low relative humidity and strong winds have created
dangerous fire weather conditions across portions of the mts and
high deserts late today. A red flag warning is in effect for the
mts/deserts and since the heat will be easing, the heat advisories
and warnings have been cancelled.
The development of any widespread stratus/fog overnight still
appears unlikely, despite the onshore flow. It appears the indirect
circulation associated with a mid-level jet streak is resulting in
subsidence over the California bight and will discourage the redevelopment
of marine layer clouds until sometime tomorrow. It will also keep
the inversion very low, so if anything, there may be patchy dense
fog along the immediate coast by morning, otherwise clear.
A minor forecast update was issued this evening to add some smoke to
the Coachella Valley and Riverside County mts and reduce the stratus
and fog over the coastal waters and coastal areas. Also to remove
the heat headlines.
From previous discussion...
The heat is just off sunday's pace with temps averaging a degree
or two lower than Sunday at this time for many areas. Some areas
are hotter, however. Look for a few daily Max temp records this
afternoon. A patch of persistent fog continues to hang along the
San Diego coast and it is rather dense. Our dominant high pressure
ridge has begun to erode and that will continue as a low pressure
trough pushes the ridge a little southward through Wednesday.
That will bring cooler weather to all areas for the coming week.
The increase in onshore flow will push some locally strong winds
through the desert slopes of the mountains and through the
deserts the next few days (see fire weather info below). While
the marine layer will take time to develop, only a few patches of
coastal fog is expected tonight. Lower pressure aloft and an
intermittent eddy circulation will rebuild the marine layer and
form a more uniform cloud deck Tuesday night and beyond. Coastal
clouds and fog will extend farther inland into some valleys each
night and morning. Rather persistent weather through the coming
weekend with only minor fluctuations in coastal cloud/fog
coverage and temperatures. Temps will get much closer to seasonal
averages by Wednesday.
270300z...coast...clear skies and unrestricted vis will prevail this
evening. Patchy fog will likely form along the immediate coast,
mainly San Diego County, after 08z with vis of 1/4 mile or less
accompanied by cigs of less than 300 ft mean sea level possible. Confidence is
low of fog reaching any airports, including ksan and kcrq. Most
areas should clear by 16z Tue. Stratus is likely Tuesday night with
somewhat higher cloud bases.
Valleys...clear skies with unrestricted vis will prevail through Tue
evening, except vicinity kbuo where smoke will occur tonight, possibly
Mountains/deserts...except for smoke near San Gorgonio Pass and
aloft vicinity kpsp and ktrm tonight and possibly Tue, clear skies with
unrestricted vis will prevail through Tue evening. Strong gusty
winds will occur from the mountain crests east through the desert
slopes and locally into the deserts through 05z with west-SW gusts 35-
55 knots, then gradually weakening late tonight and Tuesday with west-
SW gusts 25-35 knots. Occasional low level wind shear will occur over and east of
the mountains through Tuesday evening.
patchy dense fog could occur late tonight and Tuesday morning over
the coastal waters with vis below 1 mile. Stronger west-northwest winds Tuesday
evening near San Clemente Island could bring local gusts 20-25 kt.
onshore flow will bring stronger and gusty southwest to west winds
to the desert slopes of the mountains into adjacent desert. The
winds in the High Desert and north slopes of the mountains will
decrease late tonight and Tuesday, but continue strong and gusty
along the east slopes of the mountains into the lower deserts
through Tuesday night. Lowest daytime humidities will fall to
around 5 percent with poor overnight recovery. The combination of
strong gusty winds and low humidities will bring critical fire
weather conditions for the desert slopes of the mountains into
adjacent deserts. A red flag warning has been issued. Winds will
weaken some Wednesday with slowly increasing humidity Wednesday
night and Thursday.
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.
Red flag warning until 1 am PDT Tuesday for Victor valley-Apple
Valley-Lucerne Valley-Johnson Valley.