Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service San Diego California
922 am PST Fri Nov 24 2017
a ridge aloft over the southwest will be displaced by a fast-moving
trough from the northwest by Monday. The weakening ridge and a
developing coastal eddy will increase onshore flow this weekend.
Temperatures will remain well above normal again today, then
noticeably cooler Saturday through Monday. As the marine layer
returns, areas of dense fog could return to coastal areas this
weekend, and some patchy drizzle is possible by Monday morning.
Gusty westerly winds will develop over the mountains and deserts
Sunday night through Monday, turning offshore again by Tuesday
morning as the trough passes to the east. Dry and seasonally mild
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
No changes to the ongoing forecast database this morning.
Temperatures are trending as much as 10 degrees cooler this morning
compared to 24 hours ago. Light offshore gradients continue this
morning but much weaker at 3 to 5 mb from the coast to the Great
Basin. Temps away from the coast will still be well above normal
today, as much as 15 degrees above normal.
..early morning forecast discussion...
Other than some scattered high cirrus, skies were clear across
socal, including the coastal waters. Surface pressure gradients were
trending a bit more onshore and peak wind gust reports were under 20
miles per hour at 3 am PST. Temps were running a few degrees lower than 24
Expect another warm and dry day today, but the offshore gradient and
associated flow has weakened, so the sea breeze should become better
established through the day, gradually cooling coastal areas. This
trend will continue through the weekend, with cooler and moister
marine air making inroads through the valleys.
The marine air is already recovering well offshore where a San
Clemente Island observation at around 200 ft mean sea level reports dewpoints
back into the upper 50s. This recovery will reach the coast tonight
as a shallow layer that may turn to dense fog by Sat morning. A
repeat performance is possible, extending farther inland Sun
By Monday, a vigorous Pacific shortwave trough will be digging
across the region, generating gusty onshore winds over the mts/
deserts. Some patchy drizzle/sprinkles are not out of the question
west of the mts as the marine layer rockets upward in response to
the wave. Once it passes though, the marine layer will subside
rapidly as offshore gradients develop. Some locally gusty offshore
winds are likely by Tuesday morning, but this looks short-lived as
the trough moves quickly east and height recovery is muted due to
more incoming shortwave energy.
The operational model runs diverge a bit more through next week, but
there is some agreement for another offshore event to materialize by
the end of the work week. It remains to be seen if this will be
noteworthy since a split flow is developing over the eastpac, which
increases pattern uncertainty here over socal. In any case, the
pattern remains dry and mild.
241630z...fog may develop after 06z Saturday with a small chance of
vis below 1 mile and cigs below 500 ft mean sea level along the coast and up to
5 miles inland, although confidence is low. Otherwise few-scattered clouds
at or above fl200 and unrestricted vis through Saturday.
areas of dense fog may develop over the coastal waters late tonight
into Saturday morning and again Saturday night into Sunday morning.
Visibility may be reduced to 1 nm or less at times.
A trough of low pressure moving through on Monday will bring gusty
northwest winds 20 to 25 kt over the outer waters.
the wildfire threat will ease today due to light winds, but after a
couple of very warm days, it remains very dry out there, and with
minimum relative humidity in the teens again today, fire weather conditions will
still be slightly elevated inland beyond ten miles of the coast.
Gusty onshore winds will develop Sunday night through Monday. This
will elevate the wildfire threat along the highest terrain and along
the desert slopes, but relative humidity should remain above critical levels.
For next Tuesday...winds turn back offshore and may be locally gusty
below favored passes and canyons. The wind and lower humidity will
again raise wildfire concerns west of the mts due to the very dry
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.