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fxus66 ksgx 180535 aaa 
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Area forecast discussion 
National Weather Service San Diego California 
930 PM PST Sat Feb 17 2018 


Synopsis... 
a cold low pressure system will be moving into the Great Basin 
Sunday and Monday. Strong westerly winds will develop over the 
mountains and deserts, and some light rain and snow showers may 
break out, creating wintery conditions over the mountains Sunday 
night through Monday night. Dry and a little warmer midweek, then 
cooler again next weekend with another chance for light 
precipitation as another cold trough moves south along the coast. 


&& 


Discussion...for extreme southwestern California including Orange... 
San Diego...western Riverside and southwestern San Bernardino 
counties... 


Winter Weather Advisory and Wind Advisory headlines were added to 
the forecast for the upcoming cold winter storm. The low clouds were 
removed from the forecast for this evening although we will probably 
see some scattered low clouds develop by Sunday morning. No other 
significant changes were made to the forecast this evening. 
Otherwise the previous forecast discussion remains valid below. 


..previous forecast discussion... 


Our string of exceptional winter weather is about to come to an end 
as the atmosphere undergoes an adjustment favoring troughing over 
the west. Monday could be the coolest day over a good chunk of the 
County Warning Area since last winter. A large, cold, low pressure trough will drop 
into the Great Basin through Monday. It will drop sfc pressure over 
the interior west, and force strong onshore flow across socal. Winds 
will be strongest over the mts. Deserts, and coastal waters. Wind 
and winter weather products may be needed for the mts/deserts as 
well as the coastal waters for the Sunday afternoon through Monday 
evening period. 


Some light precip will break out over and west of the mts as well, 
and even though amounts will be limited, low snow-levels may create 
an impact to travelers through the mtn passes and at resort levels, 
especially later Mon/Mon night when the snow level will fall below 
3000 feet in some areas. Up to a few inches of snow could accumulate 
in some spots above 4500 feet by Tue morning, but the main impact will 
be low windchills. 


It will be much cooler through Tuesday. Maximum daytime temperatures 
on Monday may not get out of the 50s west of the mts, 30s at mtn 
resorts, and 40s over the high deserts. This equates to widespread 
maximum daytime temps of from 8 to 15 degrees below average. 


Some moderation in temperatures will occur during the midweek 
period, but continued troughing over the west will keep them below 
average for this time of year. Generally, the European model (ecmwf) model has 
handled the transition to lower heights/thickness over the west 
better than the GFS operational runs. If we follow the latest 12z 
run into next weekend, it looks like another cold trough could drop 
south over the west with another chance of light precip and well 
below average temps. 


&& 


Aviation... 
180500z...areas of stratus/fog will likely reach the coast between 
12z and 15z sun. Cloud bases will initially be low, 600 feet mean sea level or 
less, but will rise rapidly around 15z sun. The initial low bases 
could affect ksan, kcrq and ksna. Areas of vis below 3 miles will 
likely occur over higher coastal terrain 12z-15z sun, but mostly 
improve after 15z sun. Otherwise, occasional high clouds above 20000 
ft mean sea level will continue through Sunday. Clouds will increase rapidly 
Sunday evening from the mountains west to the coast, with bases 
mostly 2000-3000 ft mean sea level with higher terrain obscured, and rain showers could 
develop late Sunday night. 


&& 


Marine... 
no hazardous weather is expected through Sunday. West-northwest 
winds will increase to 20-35 kt late Sunday night and continue 
through Monday night with local gusts to 40 kt possible in the outer 
waters Monday morning. A gale watch has been issued for the outer 
waters 10 PM Sunday through 6 am Tuesday where highest winds will 
occur, with a Small Craft Advisory in the inner waters for the same 
period. Combined seas of 7-13 ft with steep waves are likely Sunday 
night through early Tuesday. Conditions will improve Tuesday. 


&& 


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


&& 


Sgx watches/warnings/advisories... 
California...Winter Weather Advisory from 6 PM Sunday to 10 PM PST Monday for 
Riverside County mountains-San Bernardino County mountains- 
San Diego County mountains. 


Wind Advisory from 2 PM Sunday to 6 PM PST Monday for apple and 
Lucerne valleys-Coachella Valley-San Diego County deserts- 
San Gorgonio Pass near Banning. 


Pz...gale watch from Sunday evening through late Monday night for 
waters from San Mateo Point to the Mexican border extending 
30 to 60 nm out including San Clemente Island. 


Small Craft Advisory from 10 PM Sunday to 6 am PST Tuesday for 
coastal waters from San Mateo Point to the Mexican border 
and out to 30 nm. 


&& 






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