Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 181117

Area Forecast Discussion
National Weather Service San Diego CA
315 AM PST Sat Jan 18 2020

This weekends weather will be dry and mild with weak high pressure
aloft and offshore flow at the surface. Next week a trough will
bring cooler weather with more clouds and perhaps a little light
rain Tuesday night or Wednesday. High pressure rebuilds late in the
week for dry, mild weather Thursday and Friday.



This weather this weekend will be warmer than it has been in quite a
while with high temperatures in the 70s west of the mountains. The
last time highs were in 70s in the coastal and valley zones was
eleven days ago, back on January 7th during a Santa Ana event.
Downslope flow combined with higher heights from ridging aloft will
account for the warming.

A 1040 mb surface high will build over western Wyoming this weekend,
strong enough for easterly offshore winds of 15 to 30 mph to funnel
through our local mountain passes and into the foothills and inland
valleys. Sunday will be the warmest day and the 70 degree highs will
be most widespread that day, perhaps reaching the upper 70s in a few
spots. The Mountains and Deserts will also be warmer too with highs
in the High Deserts and Mountains in the 50s and 60s. Lower Desert
highs will be in the 70s.

Cooler weather returns next week. The ridge breaks down Sunday night
ahead of an approaching Pacific trough for cooler weather,
increasing clouds and gusty mountain and desert winds Monday through
Wednesday. There aren`t any significant shortwaves or any band of
deep layer moisture with the weak shortwaves that will trek across
SoCal early next week, so the precip chances are slim and any
amounts will be light. Perhaps the best chance for precip will be
with a shortwave Tuesday night into Wednesday, but the arrival time
of these small shortwaves in the fast flow aloft will be another
forecast challenge.

The trough moves east Wednesday night followed by weak ridging
Thursday for dry, mild weather. Beyond Thursday the flow fluctuates
between weak ridging and weak troughing. Ensembles suggest 500 mb
heights at or just below average next weekend for weather that will
be a little cooler than average. There are weak signals that a
trough may develop along the West Coast next weekend for what might
be our next real chance for precip.


180950Z...VFR conditions expected with SCT-BKN high clouds AOA 20000
ft MSL through the TAF period. Light winds, with only weak sea
breeze expected at coastal TAF sites in the afternoon Sat.


Expect an increase in wave height on Wednesday over the extreme
southwestern portions of the Outer Waters south of San Clemente
Island. The new NW swell will generate seas of 6-8 ft. Otherwise, no
hazardous marine conditions are expected.


Skywarn activation will not be needed this weekend.





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