Weather

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


Discussion...have updated forecast to cancel advisory for the 
Northern Hills area. Accumulating snows have shifted north into 
far northwestern South Dakota...though not expecting much 
additional accumulation up there this morning...maybe an inch or 
two in spots. Toyed with the idea of killing entire advisory...but will 
keep it going for Harding and Perkins counties...with some 
potential for intensification of snowfall up there over the next 
couple of hours. Otherwise...radar showing patchy light rain and 
snow elsewhere...mostly in the form of flurries or drizzle. Custer 
has reported some light freezing drizzle over the last couple of 
hours. Snowfall amounts across northeast Wyoming...the hills...and 
northwest South Dakota have generally been in the 1 to 3 inches range...with 
some higher amounts noted across the Northern Hills area and the 
higher elevations. Only minor modifications made to forecast for 
the morning hours. 


&& 


Previous discussion... /issued 417 am MDT Friday Oct 10 2008/ 


Discussion...current surface analysis shows low pressure over 
northeastern Colorado...with frontal boundary draped across the Central 
High plains. 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 few days. It is still looking like a significant 
snowstorm will take shape across northern and western parts of the 
County Warning Area later Saturday and Saturday night. 


Strong wave has moved through the area overnight...with imbedded 
lightning strikes showing just how strong it is. Rain has fallen 
east of the hills...with mostly snow across northeast Wyoming...the 
hills...and far northwestern South Dakota. Several inches of accumulation 
has been noted in a few areas where heavier convective bands have 
moved through. Have expanded the Winter Weather Advisory to cover all 
of far northwestern South Dakota...the Northern Hills and foothills...as 
well as the Wyoming hills. It looks like the heavier bands of snow 
have tapered off some...but additional snowfall of 1 to 3 inches 
can be expected early this morning for much of the advisory 
area...especially north of the hills into Butte and Harding 
counties. Accumulating snowfall should taper off by late morning 
as temperatures slowly moderate and heavier precipitation moves out of the area. 


For later today...expecting rain and snow to continue at times 
across northern and western parts of the County Warning Area...with precipitation chances 
lowering the further south and east you go. Highs will range from 
the middle to upper 30s across northeast Wyoming...the hills...and far 
northwest South Dakota...to near 60 over south central South Dakota. Winds will be 
breezy at times from the north-northeast. 


The next significant disturbance 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 look like a good possibility from 
northeast Wyoming into the Black Hills...with rain further east. 
Debated on how to handle the current watch...since the more 
significant snowfall looks to be later Saturday into Saturday 
night. With the potential for several more inches of accumulating 
snow again tonight in some areas...have decided to leave watch as 
is and let dayshift get a look at another series of model runs and 
decide how to handle it. 


Will probably see a bit of a break again during at least the 
first half of Saturday...as far as chances for precipitation go and heavier 
precipitation is concerned. However...a very strong disturbance is prognosticated 
to slide northeastward into the area by late in the day and move 
across much of the County Warning Area Saturday night. It will be cold enough for 
significant snowfall across northeast Wyoming...the hills...and far 
northwest South Dakota. Some accumulating snowfall is also possible a bit 
further east onto the western South Dakota plains...including the rap area. 
Some sleet could also mix in further east. A general rain can be 
expected across much of southern and west central South Dakota. 


This disturbance will move out quickly Sunday morning as 
developing upper low over the central rockies will begin to move 
northeast into the northern High Plains. If this track holds...we 
will be in the dry slot of the system Sunday morning and chances 
for precipitation will be minimal from that point on. Better chances for 
precipitation in this scenario for Sunday would generally be across the 
northern and eastern County Warning Area. Most of the area will be dry Sunday 
night with cold temperatures as skies clear out some. 


Extended...upper low will be in southern Canada by Monday am with a 
cool northwest flow across western South Dakota/northestern Wyoming. Weak/flat upper ridge will 
build into northern plains for Tuesday through thursay...bringing dry 
weather through late next week. Tuesday will see seasonal temperatures. 
Another short wave will move through flow north of area on Wednesday with precipitation 
remaining north of forecast area...but will bring slightly below normal 
temperatures for Wed/Thursday. 


Aviation...IFR/LIFR conds can be expected through the forecast period 
across northestern Wyoming and far western South Dakota as occasional rain/snow will continue 
through early Sunday as slow moving upper low approaches. Southern and 
central South Dakota can expect VFR conds with local MVFR conditions in 
any precipitation. 


&& 


Unr watches/warnings/advisories... 
South Dakota...Winter Storm Watch from late tonight through late Saturday night 
for Butte-central Black Hills-Harding-northern Black Hills- 
northern foot hills-southern Black Hills. 


Winter Weather Advisory until noon MDT today for Harding-Perkins. 


Wyoming...Winter Storm Watch from late tonight through late Saturday night 
for northeastern Crook-northern Campbell-southern Campbell- 
western Crook-Weston-Wyoming Black Hills. 


&& 


$$ 

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