Freeze Warning 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Sat Feb 17 2018

.SYNOPSIS...
A cold low pressure system will be moving into the Great Basin
Sunday and Monday. Strong westerly winds will develop over the
mountains and deserts, and some light rain and snow showers may
break out, creating wintery conditions over the mountains Sunday
night through Monday night. Dry and a little warmer midweek, then
cooler again next weekend with another chance for light
precipitation as another cold trough moves south along the Coast.

&&

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

Winter Weather Advisory and Wind Advisory headlines were added to
the forecast for the upcoming cold winter storm. The low clouds were
removed from the forecast for this evening although we will probably
see some scattered low clouds develop by Sunday morning. No other
significant changes were made to the forecast this evening.
Otherwise the previous forecast discussion remains valid below.

...Previous forecast discussion...

Our string of exceptional winter weather is about to come to an end
as the atmosphere undergoes an adjustment favoring troughing over
the West. Monday could be the coolest day over a good chunk of the
CWA since last winter. A large, cold, low pressure trough will drop
into the Great Basin through Monday. It will drop sfc pressure over
the interior west, and force strong onshore flow across SoCal. Winds
will be strongest over the mts. deserts, and coastal waters. Wind
and winter weather products may be needed for the mts/deserts as
well as the coastal waters for the Sunday afternoon through Monday
evening period.

Some light precip will break out over and west of the mts as well,
and even though amounts will be limited, low snow-levels may create
an impact to travelers through the mtn passes and at resort levels,
especially later Mon/Mon night when the snow level will fall below
3000 FT in some areas. Up to a few inches of snow could accumulate
in some spots above 4500 FT by Tue morning, but the main impact will
be low windchills.

It will be much cooler through Tuesday. Maximum daytime temperatures
on Monday may not get out of the 50s west of the mts, 30s at mtn
resorts, and 40s over the high deserts. This equates to widespread
maximum daytime temps of from 8 to 15 degrees below average.

Some moderation in temperatures will occur during the midweek
period, but continued troughing over the West will keep them below
average for this time of year. Generally, the ECMWF model has
handled the transition to lower heights/thickness over the West
better than the GFS operational runs. If we follow the latest 12Z
run into next weekend, it looks like another cold trough could drop
south over the West with another chance of light precip and well
below average temps.

&&

.AVIATION...
180500Z...Areas of stratus/fog will likely reach the coast between
12Z and 15Z Sun. Cloud bases will initially be low, 600 feet MSL or
less, but will rise rapidly around 15Z Sun. The initial low bases
could affect KSAN, KCRQ and KSNA. Areas of vis below 3 miles will
likely occur over higher coastal terrain 12Z-15Z Sun, but mostly
improve after 15Z Sun. Otherwise, occasional high clouds above 20000
ft MSL will continue through Sunday. Clouds will increase rapidly
Sunday evening from the mountains west to the coast, with bases
mostly 2000-3000 ft MSL with higher terrain obscured, and SHRA could
develop late Sunday night.

&&

.MARINE...
No hazardous weather is expected through Sunday. West-northwest
winds will increase to 20-35 kt late Sunday night and continue
through Monday night with local gusts to 40 kt possible in the outer
waters Monday morning. A gale watch has been issued for the outer
waters 10 PM Sunday through 6 AM Tuesday where highest winds will
occur, with a small craft advisory in the inner waters for the same
period. Combined seas of 7-13 ft with steep waves are likely Sunday
night through early Tuesday. Conditions will improve Tuesday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 6 PM Sunday to 10 PM PST Monday for
     Riverside County Mountains-San Bernardino County Mountains-
     San Diego County Mountains.

     Wind Advisory from 2 PM Sunday to 6 PM PST Monday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

PZ...Gale Watch from Sunday evening through late Monday night for
     Waters from San Mateo point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.

     Small Craft Advisory from 10 PM Sunday to 6 AM PST Tuesday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm.

&&

PUBLIC...jad/jmb
AVIATION/MARINE...Maxwell