Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 231630
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
830 AM PST Fri Feb 23 2018

.SYNOPSIS...
Scattered showers this morning will dissipate by early afternoon,
with skies turning partly cloudy to mostly sunny, but still much
cooler than normal. Dry and warmer for the weekend with locally
gusty northeast winds near the coastal foothills in the mornings
and strong and gusty west winds in the mountains and deserts
Saturday evening. Another low pressure system from the north will
bring more showers with low snow levels and strong and gusty west
winds in the mountains and deserts for late Monday night into
Tuesday. Forecast confidence is much lower for the middle to
latter part of next week with smaller chances for showers for
Wednesday and Thursday with increasing chances for showers for
Friday and Saturday.

&&

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

A trough is indicated over the Great Basin area this morning
according to water vapor satellite imagery. Radar imagery shows
scattered light showers in San Diego County and the San
Bernardino County mountains this morning as a vorticity max moves
through Southern California. These showers are producing light
amounts of 0.01-0.07 inches. Snow levels are at around 3500 feet
this morning with up to a couple inches of snow reported above
that level. Meanwhile, winds in the mountains and deserts are
weakening, with westerly wind gusts of only around 35-43 mph
reported over the mountain ridges/desert slopes/passes currently.
With that, have cancelled the Wind Advisory a couple hours early.
With the continued cold air mass over the region, highs today
will be 10-20 degrees below normal, with highs only in the 50s in
the coast/valleys, low 60s in the lower deserts, 40s in the high
deserts, 40s/30s in the lower mountain elevations, and 20s/10s in
the high mountain elevations.

Offshore flow will develop tonight into Saturday morning as
surface high pressure builds in the Great Basin in the wake of the
departing trough, then turn briefly onshore Saturday evening
before turning back offshore Sunday. The offshore winds
tonight/Saturday morning will be pretty weak, with local N to NE
gusts of 35 mph, but the turn to onshore winds Saturday evening
could be strong in the typical mountain ridges/desert
slopes/mountain passes and also the High Deserts, and so a Wind
Advisory may be needed for those areas. The offshore winds for
early Sunday look mostly weak once again, with local gusts of
35-40 mph through/below the passes/canyons and into the coastal
foothills. The offshore winds and weak ridging aloft building
into the area will bring drier weather and slight warming Saturday
through Sunday. Highs may reach near normal on Sunday west of the
mountains, but still colder than normal elsewhere.

Flow turns back onshore late Sunday night into Monday as a trough
digs down along the West coast. Models are in pretty good
agreement with bringing this trough Southern California Monday
night through Tuesday, likely resulting in widespread showers over
and west of the mountains and a few showers in the deserts. Precipitation
totals with this system do not appear to be too heavy at the
moment, with potential amounts of 0.10-0.50 inches in the
coast/valleys, up to 1 inch in the mountains, and a few hundredths
in the deserts. This will be another cold system, with snow
levels falling to around 3500 feet and a few inches of snow
possible above that level. Onshore flow will strengthen as well,
with another round of strong and gusty west winds in the mountains
and deserts possible Tuesday.

Forecast confidence decreases next Wednesday through the rest of
the week as the forecast models diverge in their solutions. ECMWF
shows a deep trough developing over the West coast, blanketing
California with precipitation Thursday through the weekend.
Meanwhile, the GFS keeps any storms far north of the region with
dry west to northwest flow aloft. The GFS ensemble mean seems to
favor a pattern similar to what the ECMWF shows, so the forecast
shows chances for showers in our forecast area continuing through
the rest of the week.

&&

.AVIATION...
231630Z...Coast/Valleys and Coastal Slopes...SCT035 with areas of
BKN030-040 on the coastal slopes with isolated showers through 20Z.
Snow level around 4000 ft. Skies clearing from north to south
through 23Z with WNW winds 10-20 kt gusting to 25 kt. Mostly clear
tonight.

Mountain Ridges/Deserts Slopes and Deserts...Gusty west winds 15-25
kt through 23Z with moderate up/downdrafts and LLWS on the desert
slopes. Decreasing winds after 23Z.

&&

.MARINE...
West northwest winds 15-25 kt with gusts to 30 kt and combined seas
of 6-9 ft through this evening. A Small Craft Advisory remains in
effect through 8 PM. Conditions will improve over the weekend,
though gusty west northwest winds and combined sea may pick up again
early next week as several storm systems encroach on the region.

&&

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

&&

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

PZ...Small Craft Advisory until 8 PM PST this evening 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...Harrison
AVIATION/MARINE...Moede


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