Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 051724
Area Forecast Discussion
National Weather Service San Diego CA
924 AM PST Mon Dec 5 2016
Temperatures will cool slightly through Tuesday with prevailing
onshore flow over the region. Deepening marine layer stratus
along the coast may bring patchy drizzle tonight. Weak offshore
winds will develop Wednesday-Thursday, with temperatures
returning to near average readings by Friday.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
At 900 AM, SoCal remained caught between the subtropical ridge
over the East Pacific and a broad longwave trough over the Western
US. This was bringing northwest flow to the mid and upper levels,
and advecting elevated moisture (above 500 mb) over the region.
Closer to the surface the marine layer showed strong signs of
recovery overnight, with it`s presence evident on the 00Z NKX
sounding. Skies were partly cloudy over most of SoCal with
predominantly high level cirrus, though scattered low stratus was
still hanging on along the coast.
Partly cloudy skies, light winds and near average temperatures
will prevail today. A low amplitude trough will propagate through
the Pacific NW bring increasing onshore flow and promoting eddy
development over the SoCal Bight tonight. This will deepen the
marine layer and produce patchy drizzle overnight.
The aforementioned shortwave will shift rapidly eastward through
the Intermountain West on Tuesday, as a cold 1046 mb surface high
builds southward over eastern WY/MT by Thursday. This will bring
breezy mountain/desert winds Tuesday and temperature falls,
especially over the mountains and Apple/Lucerne Valleys on
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.
051700Z...Coast/Valleys...Areas of BKN stratus with rising bases,
mostly 1200-2000 ft MSL, will continue this morning, gradually
becoming SCT 18Z-21Z. Tops will be around 2000 ft MSL. Most vis will
be unrestricted. BKN/OVC stratus will become widespread in coastal
and valley areas tonight with bases mostly 2000-2500 ft MSL with
tops to 3500 ft MSL with areas of higher terrain obscured and slow
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 stratus/fog, but
otherwise visibilities will be unrestricted through Tuesday.
No hazardous marine weather is expected today through Friday.
No fire weather concerns through Tuesday with onshore flow and
increasing relative humidity. Weak offshore winds will bring
falling relative humidity values Wednesday-Thursday, with values
as low as 10% Thursday afternoon. This may produce locally
elevated fire weather conditions, however the weakness of the
winds will limit the overall threat. Onshore flow will bring
increasing relative humidity Friday, effectively squashing any
fire weather concerns by the weekend.
Skywarn activation will not be needed today.