Weather

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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
911 PM MDT Friday Oct 10 2008 


Update...water vapor imagery and radar returns show that best 
large scale lift is located over western Wyoming at this time which the 00z WRF/RUC 
have picked up on. There seems to be little upstream energy that 
would affect our South Dakota zones overnight. Thus...the best chance for 
any significant snow overnight should remain no further east than 
our northestern Wyoming zones...and even in that area would expect it to be 
confined mostly to Campbell County and higher elevations of Crook 
County. Have canceled the advisory for Weston County as well as 
the South Dakota Black Hills and northwestern South Dakota. 


Even better chance for accumulation snows still look to be on pace 
for Saturday night so the Winter Storm Warning/advisory for that 
time period still look good. 


&& 


Previous discussion... /issued 905 PM MDT Friday Oct 10 2008/ 


Current surface analysis shows low pressure over central 
Colorado...with frontal boundary draped across central Nebraska 
and southeastern South Dakota. Upper level analysis has strong 
trough continuing to dig southward across the western Continental U.S.. strong 
jet in place is bringing a series of disturbances around the base 
of the trough and into The Rockies and northern plains region. This 
is a complicated system and will bring a wide variety of weather 
across the County Warning Area over the next 48 hours. It is still looking like a 
significant snowstorm will take shape across northern and western 
parts of the County Warning Area late Saturday evening into Sunday morning. 


Next significant disturbance located in south central Wyoming will 
move into the area this evening...with another round of rain and 
snow expected...better chances again across the northern and 
western County Warning Area. Accumulating snows will occur from northeast Wyoming into 
the Black Hills...and north into northwestern South Dakota. Have 
issued a Winter Weather Advisory for this area...with the 
expectation of 3 to 6 inches of snowfall overnight into early 
Saturday morning. 


Will probably see a bit of a break again Saturday afternoon...as 
far as chances for heavier precipitation is concerned. However...a very 
strong disturbance is prognosticated to slide northeastward into the area 
by Saturday night. It will be cold enough for significant 
snowfall across northeast Wyoming...the hills...and far northwest 
South Dakota...with some areas possibly seeing close to a foot of snow. Have 
issued a Winter Storm Warning for the same areas above for 
Saturday night into Sunday morning. Some accumulating snowfall is 
also possible a bit further east onto the western South Dakota 
plains...including the rap area. A Winter Weather Advisory will be 
in effect for the same time period for 1 to 5 inches of snow. Some 
sleet could also mix in Saturday night. A general rain can be 
expected across much of southern and central South Dakota. 


This disturbance will shift north quickly Sunday afternoon as the 
developing upper low over the central rockies will begin to move 
northeast into the northern High Plains. Some lingering rain or 
snow showers will be possible across northwestern South Dakota 
Sunday afternoon and evening. 


Extended...upper low will pull away from the region Monday...but 
backwash moisture will leave some lingering -shrasn in the north 
Monday. Weak flat upper ridge will then build into the area for the 
rest of next week bringing warmer temperatures...but still 5-10f 
below normal. Highs Monday will be even colder over the expected 
snow cover in northeastern Wyoming and northwestern South Dakota. 


Aviation...widespread IFR/LIFR conditions expected through the 
period due to rasn/dz/br. 


&& 


Unr watches/warnings/advisories... 
South Dakota...Winter Storm Warning from 6 PM Saturday to 12 PM MDT Sunday for 
Butte-central Black Hills-Harding-northern Black Hills- 
northern foot hills-southern Black Hills-Sturgis/Piedmont 
foot hills. 


Winter Weather Advisory from 6 PM Saturday to 12 PM MDT Sunday 
for Custer Colorado plains-Hermosa foot hills-northern Meade Colorado 
plains-Pennington Colorado plains-Perkins-Rapid City-southern 
foot hills-southern Meade Colorado plains. 


Wyoming...Winter Weather Advisory until 12 PM MDT Saturday for 
northeastern Crook-northern Campbell-southern Campbell- 
western Crook-Wyoming Black Hills. 


Winter Storm Warning from 6 PM Saturday to 12 PM MDT Sunday for 
northeastern Crook-northern Campbell-southern Campbell- 
western Crook-Weston-Wyoming Black Hills. 


&& 


$$ 
Johnson