Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 022158
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
155 PM PST Tue Mar 2 2021

.SYNOPSIS...
Skies will be mostly clear tonight, followed by increasing clouds
Wednesday morning. Rain and mountain snow are likely Wednesday
afternoon, and there is a slight chance of thunderstorms west of the
mountains. The precipitation will taper off in the evening and end
late Wednesday night. Dry with gradual warming Thursday and Friday.
A weak trough on Saturday will bring colder weather, gusty winds and
a chance for light showers. Sunday and Monday with be dry, breezy
and cool.

&&

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

The airmass was very dry this morning with a PW of only 0.13" on the
12Z NKX sounding. Low level moisture has started a slow return to
the coastal areas this afternoon where dewpoints at Noon were 10 to
30 degrees higher than at the same time yesterday. Even with the
increase, the dewpoint was still only 42 at Imperial Beach, 32 at
Oceanside, and 21 at the San Diego Airport at Noon.

Deep layer saturation will take place tomorrow morning as a Pacific
trough pulls subtropical moisture into SoCal. Wednesday morning will
be mostly dry, but by noon the atmosphere will be nearly saturated
from the surface to 15,000 feet, and precipitation is likely in the
afternoon and evening. Max temperatures Monday will likely occur in
the late morning hours before the rain begins, with afternoon
temperatures slowly falling. The storm track favors greatest rain
totals in San Diego County and lesser amounts to the north.

Rain totals of 0.25" to 0.50" are forecast in the coastal and
valleys zones, with perhaps as much as 0.75" in parts of San Diego
County. In the mountains the amounts will range from 0.50" to 1.00",
locally higher in San Diego County. A thunderstorm is possible in
the afternoon and evening when the cold core aloft results in
steeper lapse rates and greater instability. CAPE values increase to
300-600 J/kg.

Evaporative cooling will play a role in snow levels with the onset
of the precip. Wet bulb zero heights start out near 4,500 feet
Wednesday morning, and the precip may start out as snow at that
level. Wet bulb zero heights slowly rise thereafter as the airmass
saturates and warms in the southerly flow ahead of the trough. A
Winter Weather Advisory will be in effect from 1 PM to 10 PM
Wednesday above 5,000 feet in the SBD and RIV County mountains, and
above 5,500 feet in the SAN County mountains. Snow amounts will
range from a Trace to 1" at 5,000 feet, 1-3" from 5,000-7,500 ft,
and from 3-6" above 7,500 feet. Precipitation will end late
Wednesday night.

The precipitation ends late Thursday night in the mountains followed
by a transitory ridge that will bring dry, cool weather Thursday and
dry, warmer weather Friday.

Over the weekend a weak low pressure trough will move inland across
California. This feature is trending farther north and a little
weaker, and the chances for light precipitation here in Southern
California on Saturday are low. Another weak ridge will bring dry
weather and seasonal temperatures Sunday.

The ensemble outlook for next week shows a progressive pattern over
Pacific with two shortwaves making landfall on the West Coast.
Timing and intensity differences have yet to be ironed out, but an
early precipitation projection is for rain and mountain snow Tuesday
and again Thursday. Temperatures next week will generally be below
average.

&&

.AVIATION...
022200Z...Coastal areas...Patchy low clouds and fog will be possible
after 04z Wed VCTNY KSAN, though confidence remains low on CIGS.
Increasing S-SW winds 14-16z Wed with gusts to 25 kts, isolated
gusts to 30 kts possible.

...Mountains, Valleys, Deserts...Breezy E-NE winds to occur this
afternoon with gusts of 20 to 25 kts. Winds to diminish into this
evening. Gusty S-SW winds to develop after 08z Wed and continue
through the afternoon, with winds of 35 to 45 kts, isolated gusts to
50 kts. Areas of LLWS and mod-stg up/downdrafts possible along the
mtn slopes and areas east.

Otherwise, SCT-BKN AOA 25000 FT MSL today and tonight. Widespread
cloud cover developing after 14z Wed and spreading inland, with
bases 1500-2500 FT MSL. SHRA and TSRA occurring after 17z Wed.

&&

.MARINE...
Gusty south to southwest winds 15 to 20 kts with gusts to 25 kts
along the coast Wednesday morning, with isolated gusts up to 30 kts
possible. Isolated thunderstorms are possible Wednesday afternoon
and evening. No hazardous marine weather is expected Thursday and
Friday. Breezy northwest winds will be possible Saturday afternoon
across the outer coastal waters.

&&

.BEACHES...
Isolated thunderstorms will be possible late Wednesday morning into
early Wednesday evening. Storms will be capable of producing
lightning and gusty and erratic winds.

&&

.SKYWARN...
Skywarn activation may be activated Wednesday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 1 PM to 10 PM PST Wednesday for
     Riverside County Mountains-San Bernardino County Mountains.

PZ...Small Craft Advisory from 6 AM to 6 PM PST Wednesday for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm-Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

&&

$$

PUBLIC...Moede
AVIATION/MARINE/BEACHES...Schenk



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