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Area Forecast Discussion (AFD)

Issued by Sacramento, CA (STO)

                            
775 
FXUS66 KSTO 192303
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
303 PM PST Mon Feb 19 2018


.SYNOPSIS...
A cold weather system will bring scattered snow showers across 
the Sierra through the early evening. Record cold temperatures 
with widespread freezing conditions tonight. Unsettled pattern 
continues through the week. 

&&

.DISCUSSION...
Unseasonably deep trough has dropped south over California
bringing a cold airmass to NorCal. Widespread freezing 
temperatures occurred last night/Monday morning over the area and 
expect even colder temperatures tonight. Record low temperatures 
are forcasted at most locations tonight. Widespread readings in 
the lower/upper 20's are likely with damage to sensitive plants 
and trees possible. Have upgraded the the freeze warning to a hard
freeze warning to emphasize the potential agricultural damage and
threat to freezing of outdoor pipes. Slightly warmer lows 
possible Wednesday morning, but will keep hard freeze wording 
given possibly lower readings if skies stay clear.

Instability and disturbance passing over the Sierra with cold
airmass is causing scattered snow showers and graupel. Isolated
amounts up to 3 inches will be possible through sunset with
visibilities under a mile at times. Travel delays in holiday
traffic for Mountain travel is likely.

Another cold system will track south over NorCal Wednesday and
Thursday. Moisture will be limited with this system, but a few
inches of mountain snow will be possible. Snow levels down to 1000
feet could give a dusting down to the foothills and lower
elevations of Shasta county. Valley precip amounts are expected to
be less than 0.10 inches.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)

Precipitation is expected to linger into early Friday behind the 
shortwave trough, mainly over the southeastern portion of the
forecast area. Additional accumulations will only be a few
hundredths of an inch of liquid precipitation, though areas down 
to around 2000 feet elevation could see snow flurries. Gusty 
northerly winds are expected across the western valley on Friday 
in the wake of the trough passage. Another shortwave trough could 
bring another round of precipitation to the area Saturday and 
Sunday, though current model runs are still not in good agreement.
Have continued to forecast a middle of the road situation for 
this event. Daytime temperatures are forecasted fairly steady in 
the mid to upper 50s for the valley and 20s to 40s for the 
mountains. Overnight temperatures will remain colder than normal 
in the mid to upper 30s for the valley and teens to 20s for the 
mountains. HEC

&&

.AVIATION...

VFR conditions across Valley TAF sites the next 24 hours.
Scattered snow showers with IFR/LIFR conditions will continue over
the mountains through 6z Tuesday. Winds NW 5-15 kt with local 
gusts to 25 kt, then weakening tonight.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Hard Freeze Warning until 8 AM PST Wednesday for Carquinez Strait
and Delta-Central Sacramento Valley-Clear Lake/Southern Lake 
County- Motherlode-Northeast Foothills/Sacramento Valley-Northern 
Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / 
Northern Shasta County-Southern Sacramento Valley.

&&

$$