Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 060427
Area Forecast Discussion
National Weather Service San Diego CA
827 PM PST Mon Dec 5 2016
Cloudy and not as cool tonight, but cooler on Tuesday due to more
cloud cover and prevailing onshore flow. Deepening marine layer
stratus may bring a few light rain showers or patchy drizzle at times
through Tuesday night. Weak offshore winds will push the marine
stratus back offshore later on Wednesday, with fair and warmer
weather for the balance of the work week.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
At 8 PM PDT...satellite imagery showed low clouds blossoming west of
the mts. The developing cloud pattern offshore, coupled with the S-SE
winds observed at coastal sites confirms the eddy circulation
forecast by the hi res models. Even the 00Z miramar sounding had S-SE
winds around 8-10 KTS up through 3500 FT. A weak 4 degree C inversion
was based just above 2K FT.
A weak shortwave will zip by to our NE overnight, followed by a
stronger wave that will slice across the PacNW and over the Great
Basin on Tuesday. These systems are supporting sfc pressure falls
across the interior West which will reinforce the onshore flow over
SoCal through Tue and maintain the coastal eddy and extensive
marine clouds. Given the rapid deepening of the marine layer
overnight and the depth of saturation indicated on some of the hires
model soundings, some patchy drizzle or scattered, light rain showers
are possible at times through Tue.
Fair over the deserts, but expect limited sun along and west of the
mts on Tue with gusty westerly winds over the mts/deserts. High temps
will be from 3 to 9 degrees F below average west of the mts, ranging
to about average over the deserts. Not as cold overnights though, due
to the cloud cover and wind in some areas. No changes to the forecast
are indicated at this time.
From previous discussion...
The aforementioned shortwave will shift rapidly eastward through
the Intermountain West tomorrow, as a cold 1046 mb surface high
builds southward over eastern WY/MT by Thursday. This will bring
breezy mountain/desert winds tomorrow and temperature falls,
especially over the mountains and Apple/Lucerne Valleys Wednesday.
Weak offshore winds will develop Wednesday-Thursday. These winds
should be limited to sub advisory levels by a lack of upper level
support and weak surface gradients due to a surface high (around
1024 mb) off the SoCal coast. Temperatures will return to near
average values by Friday.
Onshore flow will return over the weekend as several weak
shortwaves work their way through the Pacific NW and Northern CA.
Prevailing northwest flow aloft may bring a fading plume of
subtropical moisture and increasing high clouds to SoCal by
Sunday, but forcing appears to weak for any light precipitation
chances to be added to the forecast at this time.
060330Z...Coast/Valleys...Areas of low clouds will become widespread
overnight with bases mostly 2000-2500 ft MSL and tops to 3500 ft MSL
with areas of higher terrain obscured. Low clouds could reach KONT
aft 08Z and possibly also KSBD aft 09Z. Expect partial clearing
Tuesday between 17Z and 20Z.
Mountains/Deserts...Areas of clouds at/above 15000 ft MSL will
prevail through Tuesday. Local terrain obscurations will occur
below 3500 ft MSL late tonight and Tuesday morning due to low clouds,
but otherwise visibilities will be unrestricted through Tuesday.
No hazardous marine weather is expected through Saturday.
Skywarn activation is not requested for tonight or Tuesday.