178 
fxus63 kfsd 090225 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
824 PM CST Thursday Jan 8 2009 


Discussion... 
well organized band of precipitation well under way this evening. 
Location pretty much where it is/was supposed to be and southern and 
western advisory ending at midnight still looks like a good bet. 
Only expecting in and out freezing rain or sleet for most of these 
counties with little accumulation. However...under the original 
advisory the low to middle level thermal band should stall nearby and 
could create an extended period of moderate to heavy precipitation. 
Should remain mainly snow...but not out of the question to mix in 
some sleet or freezing rain at times as warm air tries to surge 
north. The lbf sounding does show some very dry air in the warm 
layer...so a lot of wet bulbing will take place which should aid 
some in keeping mainly snow in place. 


So...no major changes to going forecast. Looks like 2-4 inches of 
snow a good bet in original advisory overnight with additional 
expected tomorrow and tomorrow night. 






&& 


Aviation... 
warm front to push across the area this evening...producing light 
snow...freezing rain...and sleet. Expect some freezing rain over 
much of the area west and south of the Interstate 29 and 90 
intersection...with snow more likely east and north. Ceilings will 
continue to fall through the evening hours and into the overnight 
with widespread IFR to LIFR. Visibilities will also drop to IFR overnight 
as fog and patchy light freezing drizzle form. Ceiling and visby improve 
tomorrow evening as high pressure builds into the area. 


&& 


Previous discussion... 
light freezing rain has been reported with radar echos over western 
portions of the County Warning Area this afternoon. Only expecting a few hundreths 
of freezing rain but should be enough to cause some travel 
problems...so have elected to issue a second Winter Weather Advisory 
until midnight mainly for freezing rain. Previous weather weather 
advisory is for SW Minnesota and Brookings County from 6 PM this evening 
until 6 PM tomorrow evening. This advisory is mainly for 
accumulation of snow...although there could be some freezing rain 
mixed in on the western and southern fringes. Tough to say where the exact 
cutoff of freezing rain/snow/sleet will be but BUFKIT soundings 
suggest a mix as far east as a line from bkx to mjq. Main 
precipitation will be over SW Minnesota after midnight as warm front pushes 
east into Minnesota. Snow chances will end over much of the County Warning Area late tonight 
but as midlevels dry out S of the warm front...expect to see at 
least some patchy freezing drizzle...provided very moist low levels 
and weak lift along an inverted surface trough. 


Forecast on Friday could be messy espec along and east of inverted trough which will 
not move much with placement from just east of Hon to fsd to spw most 
of day. NE of this line should see most widespread precipitation during the day. 
Will pbly see a brief waning of precipitation for a while in the morning...and 
then reintensify as short wave digs across eastern Dakotas. So will continue with high 
probability of precipitation east of trough with main form of precipitation being snow. GFS seems to be 
too quick compared to rest of models with short wave and will tend to go a 
little slower. Ec and Canadian give an additional 2 or 3 inches of snow 
across SW Minnesota during the day with not much west of trough except for some light 
snow as strong cold air advection squeezes out some light snow. Strongest winds will be 
west of inverted trough on Friday...so where heaviest does 
occur...blowing snow may not be too much of a pblm until short wave passes 
late in afternoon. 


Will need to keep chance of S- across eastern County Warning Area until short wave passes during the 
late evening. Surface high building in behind short wave should gradually clear skies 
out from northwest to southeast during the night along with a surge of colder air. 
Winds should remain gusty through 06z and then gradually drop off as surface 
high settles in. 


Weak warm air advection on Sat will allow for temperatures to warm into teens and 20s east 
with 30s far short wave. Weak warm front should push east to i29 by Sun morning and could 
squeeze out a few flurries mainly east of i29 during the day. Should see 
temperatures a little above norm on sun. 


Models begin to diverge Sun night and Monday with speed of digging short wave 
and associated surface low. Track is fairly similar but ec and Canadian 
faster than GFS/NAM with bulk of precipitation Sun night into Erly 
Monday...while GFS gives bulk on Monday. This looks to be a fairly 
efficient system and could squeeze out 2 to 4 inches NE of surface track. Will 
go with higher probability of precipitation across northestern half of County Warning Area Sun night into Monday along 
projected short wave path. 


Colder air will spill in behind this short wave and will remain through most of 
week with below norm temperatures. Latest ec and GFS diving another clipper 
southeastward similar to Sun night/Monday system. This is a little stronger than previous 
prognosticated and may need to up probability of precipitation if this trend continues. Could again be a 
quick 2 or 4 inch snow accumulate with this system across northestern County Warning Area Tuesday or 
Tuesday night. 




&& 


Fsd watches/warnings/advisories... 
Iowa...Winter Weather Advisory until midnight CST tonight for 
iaz001>003-012>014. 


Minnesota...Winter Weather Advisory until midnight CST tonight for mnz098. 


Winter Weather Advisory until 6 PM CST Friday for mnz071-072-080- 
081-089-090-097. 


NE...none. 
South Dakota...Winter Weather Advisory until midnight CST tonight for sdz038- 
039-053>056-060>062-066-067. 


Winter Weather Advisory until 6 PM CST Friday for sdz040. 


&& 


$$