Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 010412
AREA FORECAST DISCUSSION
National Weather Service San Diego CA
912 PM PDT WED AUG 31 2016
Patchy dense fog along the coast will be the main concern
overnight into tomorrow morning. A persistent upper level trough
along the West Coast will bring a cooling trend for the remainder
of the week, and increase the depth of the marine layer. Fire
weather conditions will be elevated in the mountains and deserts
through Saturday, but should remain below critical levels.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
For tonight and tomorrow, broad troughing will take hold along
the West Coast as a potent system moves inland in the Pacific
Northwest. Given similar surface conditions and a slightly lower
marine inversion on the 00z NKX sounding compared to yesterday,
patchy dense fog will be a concern again tonight. The best
chances for dense fog will be early tomorrow morning along the
coastal mesas, but impacts may also occur along portions of
Interstate 5, 8 and 15, and highways 52, 56, and 78. Confidence
is not high enough for a Dense Fog Advisory at this time.
Conditions will improve after 9 am tomorrow with mostly sunny
skies in the afternoon along the coast. Inland, there is a push
of monsoonal moisture forecast to move into western AZ and
Imperial County overnight into tomorrow morning. However this
moisture should remain largely east of our local mountains and
deserts. Given the moisture positioning and a forecast capping
layer near 500 mb, cumulus buildups should be flat again tomorrow
over our local mountains and deserts. Not to be forgotten, breezy
winds will produce elevated fire weather conditions during the
afternoon and evening in the mountains and deserts.
Through the weekend, temperatures will continue to trend downward
and the marine layer will deepen as the trough becomes better
established along the West Coast. This will push the morning fog
potential into the valleys, and result high temperatures that are
close to 15 F degrees below average in the valleys by Sunday.
Other areas will be 5 to 10 F degrees below average. Fire weather
conditions will continue to be elevated during the afternoons in
the mountains and deserts, with RH values of 10-25% and breezy
west to southwest winds. The greatest concern will be Saturday
afternoon when the best drying and upper level support combine.
For next week, the broad trough along the West Coast will shift
slowly eastward as the Pacific high noses into the West Coast.
With this, temperatures will inch back to near seasonal levels
and the marine layer will lower by the middle of next week.
010322Z...Coast/Valleys... Mostly unrestricted vis with a few high
clouds until around 010400 UTC when BKN-SCT low stratus clouds at
800-1400 ft above msl begin impacting terminal sights, especially
KSAN and KCRQ. From 010400-1500 UTC, stratus and patchy dense fog
gradually develops/moves further inland to 10-15 sm and further
north along the coast to impact KSNA. Bases 400-600 ft msl, tops
900- 1300 ft msl,will be common. Clouds/fog will impact areas of
the higher mesas and coastal mountains with areas of vis 3-5 sm
and local vis near zero at times from fog. KCRQ could see more
dense fog tonight, with KSAN and KSNA possibly seeing cigs/vis
lowering to 400- 600 ft agl and vis 1/2-4 sm again with VCFG.
Clearing of stratus/fog 011500-1700 UTC. Low stratus may again
have trouble clearing the coast on Thursday afternoon. Forecast
confidence high on clouds returning and timing looks good. The
visibility is a difficult forecast with fog, with the biggest
impact likely to KCRQ.
Mountains/Deserts...Unrestricted vis through Thursday night, with
mainly SCT-FEW clouds AOA 10000 ft msl mainly over the mountains and
high deserts. Forecast confidence high. Wind speed and direction are
the difficult forecast at KPSP. &&
No hazardous marine weather is expected through Monday.
Breezy southwest to westerly winds over the mountains and
deserts will combined with low RH to induce a few hours of
elevated fire weather conditions over portions of the mountains
and deserts each afternoon through Saturday. The greatest concern
looks to be Saturday afternoon. Conditions will improve some on
Sunday as moisture increases.
Skywarn activation will not be needed today.