Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 252049
Area Forecast Discussion
National Weather Service San Diego CA
149 PM PDT Tue Oct 25 2016
Fair and warmer weather is expected through Wednesday with higher
pressure aloft and night and morning low clouds in the coast and
western valleys. Another low pressure system will bring cooler
weather, with showers mainly over and west of the mountains
Thursday night through Friday. Generally fair and warmer on
Saturday before we possibly get some more showers, cooling and a
deep marine layer on Sunday as another trough moves into
California. Drier and still cool on Monday as the trough moves
into the inter-mountain west.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Water vapor satellite shows the upper level shortwave trough that
brought the thunderstorms Sunday and Monday has moved off to the
east, with a ridge to the south building north into our area. The
12Z sounding from Miramar shows a very stable atmosphere with some
moisture in the low layers. Radiation fog was reported this
morning in some of the usual locations, such as Corona, French
Valley and Ramona but cleared out late in the morning. The upper
level ridge will continue to build over our region today which,
in addition to clearing skies, will create a warmer day today.
Also, we should have a better chance for the marine layer to re-
establish itself tonight, with low clouds/fog likely in the
coastal and western valley areas.
The upper level ridge will continue to build Wednesday, producing
another day of warming, with highs reaching near normal in the
coast and western valleys, and above normal elsewhere. The ridge
will also likely make for a shallower marine layer, increasing the
chances for dense fog in the coastal areas Wednesday
night/Thursday morning. The ridge will start to weaken on Thursday
as a trough approaches California from the west. Although models
bring most of the moisture north and west of our area, there is
still a plume of 1.4 inch precipitable water that makes it into
our region in the southwesterly 850 mb flow late Thursday through
Friday. Expect to see precipitation chances increasing Thursday
night, and then widespread precipitation Friday. All precipitation
will fall as rain, as snow levels will be much too high. Overall
rain totals will be light to moderate, with the highest rainfall
amounts expected to fall in Orange county (0.15-0.25 inches), the
Inland Empire (0.15-0.25 inches) and especially the San
Bernardino county mountain coastal slopes where local amounts of
1.5 inches or greater will be possible due to efficient upslope
orographic rainfall. Meanwhile, updated forecast indicates mainly
a few hundredths to 0.10 inches possible over and west of the San
Diego county mountains, with 0.05-0.15 inches possible in the
high deserts, while only a trace to 0.05 inches are expected in
the lower deserts. Also, expect temperatures to fall below normal
on Friday with all of the clouds and precipitation.
Saturday should be a little warmer and dry as the trough weakens
and moves to the northeast and weak ridging builds a little.
Another trough will move into Northern California on Sunday,
creating stronger onshore flow, a deep marine layer, another
cool-down and possibly a few light showers over and west of the
mountains. Still cooler than normal on Monday with clearing skies
as the trough moves inland through the Inter-mountain West.
252000Z...Mostly clear skies and P6SM VIS through this afternoon.
Stratus will develop along the coast tonight, with bases around 1200
ft MSL and tops near 1600 ft MSL, and spread 15-25 miles inland into
the valleys by early Wednesday morning. VIS could lower to 2-4 SM BR
inland where low clouds near higher terrain tonight. Low clouds and
lowered VIS should improve by late Wednesday morning. Forecaster
confidence is moderate to high.
No hazardous weather conditions are expected through Thursday
afternoon. A storm system will create scattered showers across
the region late Thursday though Late Friday and also on Sunday.
Thunderstorms are also possible over the waters late Thursday
night into early Friday.
Skywarn activation will not be needed today.