National Weather Service Forecast Discussion

Dicussion provided by the National Weather Service Forecast Office located in San Diego, California

000
FXUS66 KSGX 182043
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1242 PM PST Mon Feb 18 2019

.SYNOPSIS...
After a few left-over rain and snow showers this afternoon and
evening, the cold low pressure trough over the Southern California
will move east on Tuesday with dry, but cool weather prevailing into
Wednesday morning. Frost is likely in the colder valleys each night
before more clouds and moisture arrives with the next trough later
Wednesday. Rain and snow showers could return as soon as Wednesday
afternoon, but will be more likely on Thursday into Friday morning.
This system looks a bit colder with slightly lower snow levels.
Heavy snowfall will again be possible in the higher mountains. Dry,
with a warming trend next weekend.

&&

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

&&

Satellite imagery midday still shows an abundance of cumulus over
southern San Diego County and mountain areas. Some instability is
still present and it looks like we have one weak upper-level wave to
drift south over us later today. The hires models are painting
additional showers this afternoon and evening near the mts, so POPS
have been reintroduced into the forecast. This will mostly be snow
showers this evening, but a few could drift west of the mts with
sprinkles or isolated showers. This activity should end late tonight
as the trough slips farther to the east.

Radar and satellite indications at noon are that showers are
developing over the mountains, especially Riverside County, so this
should continue into the evening for mts and adjacent desert slopes
and some valley areas, especially San Diego County. Some additional,
light snow accumulations are possible, mainly San Diego County,
followed by clearing skies and light winds late tonight. More frost
is expected the next couple of nights so Frost Advisories are in
effect for the valleys.

A broad trough covers western N.A. with ridging over the EastPac
between 140W and 160W today. Shortwave energy will be exiting SoCal,
but more is topping the ridge, over the Aleutians, and will drop
south along the British Columbia Coast on Tue, carving out another
cold low pressure center over CA/NV on Thursday. This will bring
another surge of cold, continental air south with it and spark more
showers over SoCal as early as Wednesday afternoon.

This storm system looks even colder than the last, with 1000-500 MB
thickness values falling as low as 528-530 DM by Fri morning. So
far, the ECMWF has taken the lead with this system and the latest GFS
operational runs have been following suit. As is typical with these
systems, there are numerous waves that move about the center and
tracking them properly is the key to movement and ultimate weather
generated. The leading shortwave arrives on Wednesday night, with a
second system to follow on Thursday night. This is largely an
"inside" system, but the periphery of the circulation does expand
far enough west to grab some moisture off the Pacific to enhance
precip over SoCal.

Preliminary indications are that precip could be heavier than with
the system that just moved through. Liquid equivalent QPF range form
0.75 near the Coast, to just over 1.75 inches in the mountains. This
one looks particularly good for the San Bernardino Mts to get heavy
snowfall, although present QPF had to be modified upward to reflect
this. No doubt we will need some winter weather products for this
event soon. Besides the precip, it will be quite cold with daytime
temps averaging around 15 degrees below average.

For next weekend...The flow over the Western Hemisphere becomes less
amplified, allowing a moderation in temps over the Southwest. This
should continue into next week with no precipitation expected.

&&

.AVIATION...
182035Z...High confidence in VFR conditions today and tonight.
Scattered to locally broken clouds 3000-7000 feet msl through the
afternoon. Moderate confidence on these clouds lingering this
evening. Skies slowly clearing late tonight with northerly winds in
the foothills developing and gusting up to 30 kt after 07Z Tuesday.
VFR conditions expected to continue through Tuesday.

&&

.MARINE...
Strong northwest winds will create conditions hazardous for small
craft today and tonight. No hazardous conditions are expected
Tuesday through Wednesday morning. Strong northwest winds and large
swell will develop late Wednesday as another storm system arrives.
Hazardous winds and seas are expected Wednesday night through
Thursday night.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions. Snowfall
reports are especially appreciated today.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory from 10 PM this evening to 9 AM PST Tuesday for
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Valleys.

     Frost Advisory from 10 PM Tuesday to 9 AM PST Wednesday for San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Valleys.

PZ...Small Craft Advisory until 2 AM PST Tuesday 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...10
AVIATION/MARINE...APR

NWS SGX Office Area Forecast Discussion