Freeze Warning 4, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
332 AM PDT Tue Oct 29 2019

.SYNOPSIS...
A brief return of onshore flow will spread cooling into the
valleys today. Strong offshore flow will develop tonight and
continue into Thursday with weak offshore flow for Friday and
Saturday, and weak onshore flow for Sunday and Monday. There will
be periods of strong and gusty east to northeast winds for late
tonight into Thursday. It will be warmer toward the coast on
Wednesday and cooler inland followed by warming of high
temperatures for Thursday through Saturday. Nights will be colder,
especially Wednesday and Thursday nights with several hours of
below freezing temperatures each night in some high desert areas.
Slow cooling will begin to spread inland on Sunday and Monday.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.SHORT TERM (Today through Thursday)...
A low pressure system moving southeastward through the Great Basin
will bring a brief return of onshore flow today. The deserts into
the mountains will warm today while the onshore flow spreads
cooling into the coast and valleys.

Behind this low pressure system, surface high pressure over the
Great Basin will bring periods of strong and gusty east to
northeast winds for late tonight into Thursday with the strongest
and most widespread winds on Wednesday.

High temperatures on Wednesday will be around 5 degrees warmer
toward the coast with the deserts 10 to 15 degrees cooler than
today. On Thursday, high temperatures will be 5 to 10 degrees
warmer than on Wednesday except near the coast.

Nights will be colder with areas of frost in high desert areas for
late tonight into Wednesday morning and with several hours of
below freezing temperatures for night desert areas for Wednesday
night and Thursday night with lowest temperatures in the lower to
mid 20s.

&&

.LONG TERM (Friday through Monday)...
Weaker and more localized east to northeast winds will continue
near the coastal slopes of the mountains, mainly for Late Thursday
night into Friday morning and again late Friday night into
Saturday morning. Weak onshore flow will return near the coast for
Sunday and Monday.

It will continue to be very dry inland on Friday and Saturday with
a slow recovery in humidity for inland areas on Sunday and
Monday. Some patchy low clouds could return near the coast for
late Sunday night into Monday morning.

It will be warmer for Friday and Saturday with Saturday high
temperatures near to around 5 degrees above average with the
largest departures from average in the valleys. Slow cooling of
high temperatures will begin to spread inland on Sunday and Monday
with the return of weak onshore flow.

&&

.AVIATION...
290900Z...Clear skies today and tonight. Northeast winds will
develop after 04Z over ridges, spreading over the south and west
mountain slopes and into the valleys overnight. Gusts 30-50 knots
and strong up/downdrafts and areas of LLWS.

&&

.MARINE...
Offshore flow with easterly winds are expected to produce
intermittent gusts over 20 knots Wednesday and Wednesday night.
Otherwise, no marine weather hazards are forecast through Saturday.

&&

.FIRE WEATHER...
onshore flow will spread cooling and higher coastal humidity into
the valleys today. Strong offshore flow is expected to develop
tonight into Wednesday and continue into Thursday. There will be
periods of strong and gusty east to northeast winds with the
strongest and most widespread winds on Wednesday. Lowest daytime
humidity on Wednesday and Thursday will fall to around 5 percent
with poor overnight recovery. Critical fire weather conditions
will develop tonight and continue through much of the day on
Thursday.

For Thursday night into Saturday, there will be periods of gusty
east to northeast winds, mostly 35 mph and less, late at night
into the morning each day near and below coastal mountain slopes
and below the Cajon and Banning Passes. Lowest daytime humidity
will fall to 5 to 10 percent with poor overnight recovery. This
will continue elevated to near critical fire weather conditions
into Saturday. A slow recovery in humidity with weaker winds is
expected for Sunday and Monday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 11 PM this evening to 6 PM PDT Thursday
     for Orange County Inland Areas-Riverside County Mountains-
     Including The San Jacinto Ranger District Of The San
     Bernardino National Forest-San Bernardino County Mountains-
     Including The Mountain Top And Front Country Ranger
     Districts Of The San Bernardino National Forest-San
     Bernardino and Riverside County Valleys  -The Inland Empire-
     San Diego County Inland Valleys-San Diego County Mountains-
     Including The Palomar And Descanso Ranger Districts of the
     Cleveland National Forest-San Gorgonio Pass Near Banning-
     Santa Ana Mountains-Including The Trabuco Ranger District
     of the Cleveland National Forest.

     High Wind Watch from this evening through Thursday afternoon for
     Orange County Inland Areas-Riverside County Mountains-San
     Bernardino County Mountains-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Diego County Mountains-
     San Diego County Valleys-San Gorgonio Pass Near Banning-
     Santa Ana Mountains and Foothills.

     Freeze Watch from late tonight through Friday morning for Apple
     and Lucerne Valleys.

PZ...NONE.

&&

PUBLIC/FIRE WEATHER...17
AVIATION/MARINE...MM