Weather Service Report


605 
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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