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Area forecast discussion 
National Weather Service San Diego California 
143 PM PST Sat Feb 24 2018 


Synopsis... 
slightly warmer today with dry weather and breezy westerly winds 
in the mountains and deserts. Weak to locally moderate east to 
northeast winds will develop tonight along coastal mountain slopes 
and through mountain passes. A cold low pressure system from the 
north will create showers with lower snow levels Monday night 
into Tuesday evening, along with a slight chance for 
thunderstorms on Tuesday. Drier and a little warmer for 
Wednesday, then cool and breezy with additional chances for 
showers for late Thursday through Saturday. 


&& 


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


At 1 PM PST, water vapor satellite imagery displayed an upper- 
level shortwave trough moving across central California, with 
northwest flow aloft over Southern California. Expect fair and 
cool weather today, with highs mostly 5-10 degrees below seasonal 
normals. Breezy westerly winds will develop late this afternoon 
through late this evening over the mountains and deserts as the 
trough moves by to the north. Gusts of 30-40 mph are possible, 
with isolated gusts near 50 mph in the mountains. Winds quickly 
shift east to northeast late tonight through early Sunday 
afternoon after the trough passage. 20-30 mph gusts are expected 
through mountain passes and along coastal mountain slopes. 
A frost advisory remains in effect tonight for portions of the 
inland Empire for low temperatures in the low to mid 30s. Areas 
with breezy easterly winds will have higher temperatures 
overnight. 


An upper-level low then dives south towards our region Monday and 
arrives late Monday night into Tuesday. Models have been in good 
agreement with the timing of the system, however precipitation 
amounts are still uncertain. H500 temperatures near -30 degrees c 
will create the possibility of isolated thunderstorms. 
Precipitation will be a challenge to forecast since storms could 
be convective and create highly variable amounts across the area. 
Snow levels start out around 4500 ft, then dip as low as 2500 ft. 
Current snowfall estimates for elevations above 4000 ft are 2-6 
inches, with greatest amounts in San Diego County. Locally greater 
amounts are likely in heavier showers. Highs Tuesday will dip 
down 10-20 degrees below normal. Breezy west to southwest winds 
are expected, with 40-50 mph gusts possible over the mountains and 
deserts. 


Weak ridging will build in Wednesday and early Thursday and help 
high temperatures nudge closer to normal, but still be about 5-10 
degrees below. A deep upper-level trough is expected to move 
across the area sometime late Thursday through Saturday. Models 
are in disagreement with timing and precipitation amounts as one 
would expect being 6-7 days out, however the system looks to be 
not as cold as the one earlier in the week, with current forecast 
snow levels between 4500-6000 ft. Gusty west to southwest winds 
can be expected again in the usual windy locations of the 
mountains and deserts. 


&& 


Aviation... 
242100z...clear skies with unrestricted visible will continue through 
Sunday evening. Local gusty west winds will occur late this 
afternoon and this evening on the east slopes of the mountains with 
local gusts 25-35 kt, then areas of northeast surface winds 15-25 kt 
with gusts 25-35 kt will occur Sunday morning along southwest slopes 
of the mountains and through/below passes/canyons, including vicinity 
kont, ksbd, kczz and areas north of kpsp, along with moderate-strong 
up/downdrafts. Low level wind shear will be possible in some other areas Sunday 
morning, including ksna. 


&& 


Marine... 
no hazardous marine weather is forecast through this weekend. 
Elevated winds and seas will occur Monday through early Tuesday due 
to a low pressure system. West to northwest winds will be 20-25 
knots with gusts 25-30 knots, and choppy seas of 8-10 feet will be 
possible. 


&& 


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


&& 


Sgx watches/warnings/advisories... 
California...frost advisory from midnight tonight to 8 am PST Sunday for San 
Bernardino and Riverside County valleys-the inland Empire. 


Pz...none. 
&& 






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