000 
fxus66 ksgx 190548 aaa 
afdsgx 


Area forecast discussion 
National Weather Service San Diego California 
945 PM PST sun Feb 18 2018 


Synopsis... 
onshore flow will be increasing tonight, becoming strong and gusty 
over the mountains and deserts as a cold low pressure trough drops 
south into the Great Basin. Scattered, light rain and snow showers 
will pop over and west of the mountains late tonight into Monday as 
the marine layer builds. Expect the coldest days of the winter so 
far on Monday and Tuesday. Dry and a little warmer for Wednesday and 
Thursday. Then cooler again into Friday, with a chance for some more 
scattered showers as another cold low pressure system drops into the 
Great Basin from the north. Dry and a little warmer into next 
weekend as temperatures edge back toward average. 


&& 


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


..evening update... 


Rain showers are developing offshore, likely to 
move onshore after 10 PM. Most of this activity will be quite light 
as it moves inland through the night. Snow showers will be likely in 
the mountains late tonight but again on the light side. With 
temperatures already down into the mid 40s in the High Desert, there 
is a slight chance of seeing some snow flurries by Monday morning 
there as well once the cooler air is ushered in by the vigorous 
trough which will be dropping through California overnight. No 
significant changes were needed to the forecast this evening. 


..remainder of previous discussion... 


A longwave trough will dive into the Great Basin on Monday, grazing 
socal with strong onshore winds and scattered light precipitation. 
It will also bring the coldest air of the season, plunging maximum 
temps on Monday into the 15 to 20 degrees below normal range. Given 
the extended period of well above normal temps this winter, it will 
be a profound change. 


This wave is actually the beginning of a more sustained cooler 
weather pattern for the socal as the longwave is maintained for 
sometime in the model runs. Various shorter wavelength disturbances 
will periodically drop into the longwave, creating gusty onshore 
flow over the coastal waters, mts and deserts, and chances for light 
precip. So for the foreseeable future, daytime temperatures will 
be mostly below average. 


A variety of warnings and advisories are in effect from frost/freeze 
to wind and winter conditions. Please visit our webpage for more 
detail on all of these. Of most significance will be the strong 
westerly winds late tonight into Monday. Gusts over 70 miles per hour are 
expected on the upper desert slopes and ridge tops, while on the 
desert floor, it will be breezy, but potentially damaging gusts look 
to be more isolated and near the foothills late tonight into Monday 
morning. Windy conditions are also expected for coastal San Diego 
County on Monday. Precipitation will be light and scattered, but it 
will be cold enough so that some light snow accumulations are 
forecast above 4000 feet. Freezing conditions on the passes, could 
create a hazard to travelers. 


As this system moves east, another, weaker trough slips south across 
the area midweek with little weather. Temps will moderate some, then 
a stronger disturbance drops south for Friday. This one could 
generate more light showers, and gusty winds over the mts/deserts/ 
coastal waters. Slightly warmer and dry into the weekend, then both 
the 12z GFS/European model (ecmwf) runs are advertising a stronger system early next 
week. Who knows, we may be able to salvage some precip before the 
end of the month. 


&& 


Aviation... 
190515z...mostly broken-overcast clouds with bases 2000-4000 ft mean sea level will 
prevail through Monday afternoon from the mountains to the coast, 
with scattered -shra, most frequent 07z-13z, plus scattered -shsn in 
the mountains. Higher terrain will be obscured, with tops to 8000 ft 
mean sea level possible, but at taf sites, most vis will remain above 5 miles. 
By Monday evening, most areas will have scattered clouds, generally above 
3000 ft mean sea level. 


Southwest to west winds 25-35 kt with gusts to 55 kt will continue 
to spread over the mountain crests and Desert Mountain slopes 
tonight with these strong winds continuing through Monday afternoon. 
Areas of west winds 20-30 kt will occur near the coast Monday and 
will likely bring gusts around 30 kt at ksan at times. 


&& 


Marine... 
west-northwest winds will increase to 20-30 kt tonight and continue 
through Monday night, with gusts 35 to 40 kt possible in the outer 
waters Monday morning. Combined seas of 9-13 ft with steep waves are 
likely Monday through Monday evening in the outer waters with 7-11 
ft in the inner waters. 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 this evening to 10 PM PST 
Monday for Riverside County mountains-San Bernardino County 
mountains-San Diego County mountains. 


Wind Advisory from 2 PM this afternoon to 6 PM PST Monday 
for Coachella Valley-San Diego County deserts-San Gorgonio 
Pass near Banning. 


High Wind Warning from 2 PM this afternoon to 6 PM PST Monday 
for apple and Lucerne valleys. 


Frost advisory from 10 PM Monday to 9 am PST Tuesday for San 
Diego County valleys-San Gorgonio Pass near Banning. 


Wind Advisory from 8 am to 6 PM PST Monday for San Diego County 
coastal areas-San Diego County valleys. 


Frost advisory from 10 PM Tuesday to 8 am PST Wednesday for San 
Bernardino and Riverside County valleys-the inland Empire. 


Freeze warning from 10 PM Monday to 9 am PST Tuesday for San 
Bernardino and Riverside County valleys-the inland Empire. 


Pz...Gale Warning from 10 PM this evening to 6 am PST Tuesday 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 this evening 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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