FXUS66 KSGX 261117
Area Forecast Discussion
National Weather Service San Diego CA
417 AM PDT Mon Jun 26 2017
Hot and dry conditions will continue for inland areas today.
Strong gusty southwest to west winds and low humidities will
combine to produce near critical fire weather conditions at times
for this afternoon through Tuesday evening for the desert slopes
of the mountains into adjacent desert areas. Cooling will begin to
spread inland on Tuesday with near average high temperatures
returning on Wednesday and continuing into next weekend with minor
day to day differences. Patchy low clouds and locally dense fog
near the coast will increase in coverage and spread farther inland
on Tuesday night into Wednesday morning as the marine layer
deepens with the night and morning coastal low clouds and fog
extending into portions of the valleys through next weekend.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
.SHORT TERM (Today through Wednesday)...
High pressure aloft was centered over southern Arizona Sunday with
the center moving towards to the southwest to northern Baja today
and off the northern Baja coast Tuesday. The high pressure will
weaken tonight and Tuesday as a low pressure system moves inland
through northern California and the Pacific Northwest
strengthening the onshore flow across Southern California.
West of the mountains...a strong shallow marine inversion brought
greater warming from inland coastal areas across the valleys to
the coastal foothills on Sunday. Higher resolution models show
the marine layer becoming a little shallower through this
afternoon...before gradually deepening tonight and Tuesday with
greater deepening for Tuesday night into Wednesday. The heat
advisory has been extended through today for the Inland Empire and
Santa Ana mountains and expanded to include the inland San Diego
County valleys and far inland Orange County. Slow cooling will
spread inland on Tuesday with greater cooling on Wednesday
returning high temperatures to near average.
Early this morning...satellite imagery shows areas of stratus
near the northern Baja coast extending northward near portions of
the San Diego County coast and extending locally inland. Fog could
be locally dense early this morning where it does extend inland
near the coast. Higher resolution models show a little greater
coverage near the coast for tonight into Tuesday morning with
stratus more widespread and extending inland into portions of the
valleys Tuesday night into Wednesday morning as the marine layer
.LONG TERM (Thursday through Sunday)...
Onshore flow will continue through next weekend with high pressure
remaining to the south and southwest and a weak trough of low
pressure across Southern California next weekend. There will be
minor day to day differences with high temperatures near average.
Areas of night and morning coastal low clouds and fog will extend
into portions of the valleys.
250945Z...Coast...A narrow strip of fog has developed along the San
Diego County coast this morning. Areas of vis 1/2 sm less possible
at the beaches and up to 5 miles inland through about 14Z, with
gradual clearing through 16Z. Patchy dense fog may redevelop along
the immediate coast late tonight into Tuesday morning, however
confidence in any vis restrictions at the coastal airports is low.
Otherwise mostly clear with unrestricted vis through Tuesday morning.
Valleys/Mountains/Deserts...A few shallow cu may develop over the
mountain ridges this afternoon. Otherwise mostly clear with
unrestricted vis through Tuesday morning.
A narrow strip of dense fog will continue along the San Diego county
coast and up to 15 NM offshore through mid-morning. Visibility 1 SM
or less is possible through about 8 AM. Patchy dense fog may
redevelop near the coast again late tonight.
Northwest wind gusts near San Clemente Island may reach 20-25 kt
during the afternoons and evenings through Tuesday, although the
areas of gusty winds will likely be too small to warrant a small
Onshore flow will bring stronger and gusty southwest to west winds
at times for this afternoon into Tuesday evening for the desert
slopes of the mountains into adjacent desert areas. Lowest daytime
humidities will fall to around 5 percent with poor overnight
recovery. The combination of strong gusty winds and low humidities
will bring periods of near critical fire weather conditions for
the desert slopes of the mountains into adjacent desert areas for
this afternoon into Tuesday evening. Winds will weaken some for
Wednesday with slowly increasing humidities for Wednesday night
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Heat Advisory until 9 PM PDT this evening for Riverside County
Mountains-San Bernardino County Mountains-San Bernardino
and Riverside County Valleys-The Inland Empire-San Diego
County Mountains-Santa Ana Mountains and Foothills.
Excessive Heat Warning until 9 PM PDT this evening for Coachella
Valley-San Diego County Deserts-San Gorgonio Pass Near
Heat Advisory from 10 AM this morning to 9 PM PDT this evening
for Orange County Inland Areas-San Diego County Valleys.
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