Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 251631
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
831 AM PST Sat Feb 25 2017

.SYNOPSIS...
Sunny and a little warmer midday, before a cool sea breeze develops
in the afternoon. For late tonight through Monday night...a pair of
low pressure systems from the northwest will bring cooling, gusty
winds over the mountains and desert slopes, and periods of rain and
mountain snow showers. Most of the precipitation will be light.
Quite cool again on Tuesday. Then dry and warmer into next weekend
with periods of weak offshore flow.

&&

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

Skies were clear and sunny early this morning, but it was cool with
many reporting sites reporting 7 AM PST temperatures in the 30s and
lower 40s. Surface pressure gradients to the deserts were slightly
onshore but very weak so most areas had light winds. The 12Z Miramar
sounding had a sfc-based inversion with a spike in low-level warming
of 2 to 7 degrees C in the 950-850MB layer.

Based on the sounding and clear skies, rapid warming should ensue
this morning before the sea breeze develops and levels off temps
early afternoon. It should be a bit warmer today most areas, but the
sea breeze this afternoon will be cool. forecast was updated to
remove the Frost Advisory, otherwise no changes.

From previous discussion...

The first in a pair of low pressure systems from the northwest will
move through Southern California late tonight and early Sunday with
a second for tonight and Monday. The first round of mainly light
precipitation for areas along and west of the mountains and deserts
is expected for late tonight into Sunday morning with precipitation
spreading southward across the area.

A second round of precipitation is expected for Sunday night into
Monday with showers lingering into Monday night. For this second
round of precipitation...a trough of low pressure from the
northwest will tap a plume of subtropical moisture extending into
northern Baja. The more significant precipitation is expected
across northern Baja with lighter precipitation extending into
southern portions of Southern California with the greatest
precipitation amounts for Southern California expected across San
Diego County.

For this second round of precipitation...rainfall amounts have been
increased somewhat for San Diego County from one-third to locally
one-half inch near the coast, to one-half to one inch in the
mountains, with less than one tenth inch in the deserts. Snow levels
will fluctuate around 5000 feet.

There will also be periods of gusty west winds...strongest near
the mountain ridge tops onto the desert slopes of the mountains.
The first is expected for tonight. The second is expected for
Sunday night into Monday evening. This second round is expected to
be a little stronger and more widespread.

High temperatures for Sunday and Monday are expected to be around
5 degrees below average near the coast...to 10 to 15 degrees below
average for areas farther inland.

&&

.LONG TERM (Tuesday through Friday)...
Slightly warmer for Tuesday with northwest flow aloft. For
Wednesday through Friday...high pressure aloft near the
California coast and surface high pressure over the Great Basin
will bring dry weather with a warming trend with periods of weak
offshore flow.

&&

.AVIATION...
251609Z...P6SM vis and increasing clouds AOA 15000 ft msl through
26/0000 UTC, with some SCT-FEW clouds 2000-3000 ft msl possibly
developing after 2100 UTC in the coastal areas. 26/0000-0900 UTC,
BKN cloud decks developing in the 2000-6000 ft msl layer over and
west of the mountains and also AOA 10000 ft msl all areas, with
primarily P6SM vis continuing except for mountain obscuration of
coastal slopes due to clouds. After 26/0900 UTC, showers moving into
the region (mainly over and west of the mountains) with multiple OVC-
BKN cloud decks in the 2000-15000 ft msl layer over and west of the
mountains and BKN-SCT cloud decks in the 5000-15000 ft msl layer in
the deserts. Due to showers, expect areas of vis 3-5 sm with local
vis 1-2 sm, and cigs locally dropping to 1000-1500 ft agl, with
mountain obscuration continuing.

After 26/0000 UTC, W winds strengthening, becoming 15-25 kt with
gusts 35-45 kt by 26/0900 UTC over mountain ridges, through/below
passes/canyons, and along desert slopes, resulting in mod-stg
uddfs/llws over and E of the mountains.

&&

.MARINE...
A weak storm will bring occasional showers and winds gusting to near
20 kt at times Sunday and Monday. Otherwise no hazardous marine
weather is expected through Thursday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 4 PM this afternoon to 10 PM PST Monday for
     Riverside County Mountains-San Bernardino County Mountains-
     San Diego County Mountains-San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...JAD/17
AVIATION/MARINE...Harrison


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