FXUS66 KSGX 180410
Area Forecast Discussion
National Weather Service San Diego CA
810 PM PST Sun Dec 17 2017
High pressure will bring fair skies, lighter winds and mild weather
Monday and Tuesday with seasonal temperatures. Strong onshore flow
will develop Wednesday as low pressure swings into the Great Basin,
pulling in the marine layer briefly. As the low passes, high
pressure will build inland, forcing flow back offshore across
Southern California with another round of gusty northeast winds
below passes and canyons. Cooler, with more seasonal temperatures
into the weekend.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
The Cajon Pass and areas just below along with the Santa Ana
coastal slopes continue to see northeast winds gusting 30-40 mph.
However, winds will be relaxing overnight. The Wind Advisory was
allowed to expire at 8 PM.
Temps have fallen a bit quicker in portions of the area, so
adjusted the lows for tonight down a tad, mainly for the
A strong ridge remains parked just off the West Coast. The ridge
will expand across the west on Monday, then flatten as a strong
shortwave trough slides SE from higher latitudes. The trough will
dig SE into NV on Wednesday as the ridge off the coast builds
northward. Surface pressure falls over the Great Basin will set
the stage for strong onshore flow over our mts/deserts later
Wed/Wed night, before winds turn back offshore on Thursday as the
Current indications are for westerly winds gusts of 50 to 60 MPH
over the mtn crests/desert slopes late Wednesday before swinging
northerly and then NE on Thursday. The NE winds could be quite
strong as well, especially through the passes and canyons and along
the coastal slopes of the Mts. This event looks to be short-lived
though as models show the trough moving east rather quickly.
The weekend looks like a transition period with higher uncertainty
as the hemispheric pattern begins to undergo a rather large shift.
Both the 12Z GFS/ECMWF runs appear to be hinting at establishing the
massive EastPac ridge farther to the north, allowing shortwave
energy to undercut. How this energy manifests itself remains to be
worked out, but it will at least keep us cooler and tamp down the
persistent dry offshore flow we have been experiencing this month.
The shift in the ridge, if it does occur as seems to be indicated,
will also open the door to Pacific systems that could eventually
bring much needed precipitation.
180345Z...Mostly clear with unrestricted vis through Monday evening.
A trough of low pressure moving through the region will bring
strengthening northwesterly winds gusting 20-25 kt Wednesday night
through Thursday morning.
Winds will subside overnight, with moderate RH recovery. Drier
most areas on Monday as daytime RH falls into the teens over the
mtns/valleys, but winds will be light.
Onshore flow will be increasing and become strong and gusty over the
mtns/desert slopes by Wednesday afternoon and evening as low
pressure passes to the northeast. Gusty offshore flow will follow on
Thursday and could be quite strong into Thursday night.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
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