Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 281536
AREA FORECAST DISCUSSION
National Weather Service San Diego CA
836 AM PDT SUN AUG 28 2016
High pressure to the southwest will expand into California through
Tuesday, lowering the marine layer, and bringing much warmer
weather. Cooler again by Wednesday through the upcoming holiday
weekend, as a low pressure trough develops south along the West
Coast. Areas of fog are more likely tonight and again Monday night
in the western valleys and coastal areas as the marine layer lowers.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Marine stratus was much more limited this morning, confined to
western San Diego County and offshore. The 12Z Miramar sounding
indicated a drop of around 1000 feet in the marine layer depth, with
a strong 10 degree C inversion base near 2250 FT. PW had increased
to just over one inch, with most of the added moisture below 800
MBS. Easterly winds of 15-25 KT were indicated between 8K and 13K
FT, with weak northerly flow below the inversion. The sounding was
stable. Surface pressure gradients had a weak offshore trend, and at
8 AM PDT, had turned offshore from NV, but remained weakly onshore
to the lower deserts. Winds were light.
Based on the Miramar sounding this morning, expect some clouds to
linger near the beaches of San Diego county into the afternoon,
otherwise becoming sunny. With the added moisture in the low/mid
levels, expect more cumulus clouds again over the mountains this
afternoon, but given the stability in the sounding and limited
moisture profile, no shwrs are expected. It will be warmer,
especially in the inland valleys where max temps should be some 10
degrees F above values observed yesterday. This discrepancy will
decrease with proximity to the coast.
The marine clouds will be limited again overnight into Mon morning.
Warmer most areas Mon/Tue with the marine layer decreasing further
and fog becoming more of a factor in the western valleys and
possibly along portions of the coastal strip. High Temperatures
Mon/Tue will be from 5 to 10 degrees above average most areas,
making for very warm to hot afternoons.
A high pressure ridge centered off the coast, will expand over SoCal
through Tue, then submit to a developing long wave trough along the
West Coast Wed through the end of the week. Easterly flow in the mid-
levels will turn southerly by Wed, possibly allowing a minor
moisture intrusion over the mountains and deserts, before drying SW
winds develop with the upper-level trough. There is general model
agreement on the strength and development of this long wave feature,
so confidence is building in a dry and cool Labor Day weekend.
There are currently no pops in the forecast, even though there is a
brief window when some moisture and instability arrive around mid
281501Z...Coast/Valleys...Low clouds based around 1500 feet MSL with
tops around 2300 feet MSL south of KCRQ should clear to out over the
coastal waters around 28/1700Z today. After 29/06Z this evening low
clouds pushing inland again with slightly lower bases and tops. Risk
of low clouds reaching KONT tonight is low so will keep low clouds
west of KONT. Confidence in low clouds reaching KCRQ tonight is
moderate so will continue to indicate low cloud development for
Mountains/Deserts...Mostly clear skies with unrestricted vis through
No hazardous marine weather is expected through Friday.
Skywarn activation will not be needed today.