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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
352 am MDT Sat Oct 11 2008 


Discussion...current surface analysis shows one area of low 
pressure over southeast Colorado...with another area over southern Utah. 
Upper level analysis has large trough covering the western 
Continental U.S....with low pressure over eastern Nevada. Strong jet wrapping 
around the system continues to bring a series of disturbances 
across the northern rockies and northern High Plains. Regional 
radars showing areas of precipitation...mostly snow...moving north- 
northeast across Wyoming and into northwestern South Dakota. Will keep Winter Weather 
Advisory going across northeast Wyoming as up to another couple of 
inches of accumulation are possible early this morning. Some 
areas of drizzle and light rain also noted east of the hills. Low 
clouds and some areas of fog blanket most of the region. 


For today...skies will remain cloudy...with possibly a few breaks 
across far southern South Dakota...but I doubt it. Temperatures will only rise a 
few degrees today...with highs generally in the 30s and lower 
40s...warmest toward central South Dakota. Main chances for rain and snow 
will continue to be from eastern Wyoming into the Black Hills and 
across northwestern South Dakota. Heavier precipitation will taper off early this 
morning...with a bit of a break during the late morning and early 
afternoon. Precipitation should then begin to pick up again late this 
afternoon across northeast Wyoming as next disturbance approaches. 


Forecast generally on track for the heavy snow across northern and 
western portions of the County Warning Area tonight. Strongest disturbance of the 
bunch will move into the area late today and tonight...bringing 
widespread precipitation to northeast Wyoming and western South Dakota. Precipitation will be in 
the form of snow across northeast Wyoming...the Black Hills...and far 
northwestern South Dakota. Most of this area will receive anywhere from 6 
inches to over a foot of accumulation by late Sunday morning. 
Forecast gets much trickier as you head further east on the western 
South Dakota plains. Right now...it looks like the cutoff for any 
accumulating snow will be just east of the hills and northward 
into central Meade and far western Perkins counties...but this is 
very much subject to change. For a good portion of the advisory 
area...especially Perkins...northern Meade...and eastern 
Pennington...I am not sure that an advisory is warranted. 
However...will keep it in place as there is still some potential 
for a quick few inches of heavy snow over far western portions of 
these areas if it ends up slightly cooler later tonight. Some 
sleet may mix in with the rain and snow where there is changeover. 
A general rain can be expected over eastern portions of the County Warning Area. 


Precipitation will taper off rather quickly from southwest to northeast on 
Sunday morning as upper low ejects northeastward across Wyoming and 
eventually into southeastern Montana by late in the day. This will put our 
area in a dry slot...with chances for precipitation dwindling as the day 
progresses. Best chances will be across far northeast Wyoming and 
central South Dakota by the afternoon. Will probably see some breaks in the 
clouds by the late morning and afternoon...but temperatures will stay on 
the cool side...especially over snowcovered areas. Warmest temperatures 
will again be across south central South Dakota. 


Upper low will continue to move northeastward into south central 
Canada by Monday. Upper trough will still be in place across the 
region into Monday night. This will keep the area somewhat 
unsettled and very cool during this time...but chances for precipitation 
will be low and primarily confined to northern and eastern 
portions of the forecast area. 


Extended...weak flat upper ridge will build into the area for 
Tuesday through Friday...bringing dry weather and warmer temperatures 
..though temperatures will run slightly below seasonal normals through 
the week. 


&& 


Aviation...IFR/LIFR conds can be expected through the forecast period 
across northestern Wyoming and far western South Dakota as occasional rain/snow and drizzle 
will continue through early Sunday morning as slow moving upper low 
approaches. Southern and central South Dakota can expect scattered showers with 
widespread IFR/LIFR conditions due mainly to low clouds and fog. 


&& 


Unr watches/warnings/advisories... 
South Dakota...Winter Storm Warning from 6 PM this evening 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 this evening 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 noon MDT today for northeastern 
Crook-northern Campbell-southern Campbell-western Crook- 
Wyoming Black Hills. 


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


&& 


$$