National Weather Service Forecast Discussion

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

228
FXUS66 KSGX 191632
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
832 AM PST Sun Jan 19 2020

.SYNOPSIS...
High pressure aloft and offshore flow at the surface will bring a
warm day today. Clouds will thicken tonight into Monday as a Pacific
disturbance spreads high-level moisture moisture over the region.
Scattered, light showers or sprinkles will be possible through
Tuesday night as the marine layer rebuilds inland. High pressure
aloft and weak offshore flow returns for dry and warmer weather
to wrap up the week.

&&

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

Skies were mostly clear this morning over SoCal, with a few wisps
of high clouds edging in from the west. Temperatures were a bit
milder overall this morning, but low, sheltered spots once again
fell into the 30s, including here at the office with a minimum of
35F. The sfc pressure gradient from SW NV was -12 MBS to KSAN, which
is strong and helping to fuel NE-E wind gusts of 40-50 MPH. Far and
away the strongest (58 MPH) gust has been measured at Highland
Springs (below the San Gorgonio Pass). These winds will continue
through late morning and then gradually weaken.

The 12Z Miramar sounding had further warming of 4C below 5000 FT.
This, coupled with a decent amount of sun should send afternoon
temps well into the 70s at lower elevations, which is some 5F above
average. Onshore flow will develop over coastal areas later today
and will drag some low. marine air inland over coastal areas which
could result in some patchy fog, but due to the increasing high
clouds, it is not expected to be widespread. No forecast changes
this morning.

Satellite imagery at 8 AM PST showed an impressive cloud deck well
offshore, drifting east. This is associated with a low-latitude
trough which is tapping subtropical moisture. The system will fall
apart as it approaches the Coast, but high-level moisture will
saturate the upper atmosphere, which could leak some light showers
as the clouds pass over SoCal Mon/Mon night. A dry, lower atmosphere
will evaporate some of this initially, but will become increasingly
saturated with time, and the marine layer will build as well,
helping some of the drops to survive the trip to the surface. Models
always have a difficult time quantifying this, but most have some
spotty light precip amounts later Mon and Tue and low POPS are in
the forecast. The best chance of accumulating rainfall will be along
the higher terrain of the mts, which have a shallower dry layer
above them.

Once this moisture blob passes, a marine layer will be in place west
of the mts on Wednesday, before weak offshore flow and a building
ridge aloft squeezes it back toward the Coast. This will provide
fair, dry, and warmer weather for the latter half of the week.

The 00Z ECMWF ensemble members still have a significant number of
runs with precip over SoCal early next week, but it is a precarious
path with the digging cut-off advertised off the Coast, and the GFS
ensemble members are all dry. For now, our forecast for Sunday is
for dry weather to continue.

&&

.AVIATION...
191600Z...VFR conditions with SCT-BKN high clouds AOA 20000 ft
through this evening. Locally gusty northeast to east winds of 25-30
kt expected through passes and over the mountains through this
morning. Confidence still somewhat low on cigs 300-800 ft MSL
impacting coastal TAF sites tonight 04-12Z.

&&

.MARINE...
Calm conditions through the afternoon with patchy fog possible
tonight. An incoming NW swell will generate wave heights of 6-8 ft
Wednesday into Thursday morning. Wave heights will be highest in the
far southwestern portions of the Outer Waters, south of San Clemente
Island. Otherwise, no hazardous marine conditions are expected
through Thursday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...10
AVIATION/MARINE...APR

NWS SGX Office Area Forecast Discussion