551 
fxus63 kfsd 091131 cca 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
530 am CST Friday Jan 9 2009 


Discussion... 
forecast concerns for the day deal mainly with the ongoing system... 
and then attention drifts toward the next two on Sunday night/Monday 
and Tuesday/Tuesday night. Main middle level baroclinic zone has shifted north of 
the area overnight taking the significant precipitation with it...as drier 
air blow lingering middle deck has pushed up into the i90 corridor on 
the south side of the band. Some very light precipitation has continued along 
and north of i90 in eastern South Dakota down toward the Iowa Great Lakes 
area...with groundtruth as a mix of some freezing sprinkles...sleet 
or flurries. Visibilities across the County Warning Area have been greater than 6 miles in 
last couple hours for all reporting sites...and other than the far 
northern tier from bkx to mwm areas early morning which may see some 
lingering precipitation on the edge of the moisture and as first piece of upper 
wave pushes toward central Minnesota. Main positively tilted upper wave across 
eastern Montana will continue to progress sewrd today. This will return the main 
middle level baroclinic zone southward...and esply sets up a favorable 
interaction with boundary by later this morning and esply this afternoon 
drifting sewrd through area. Temperatures do improve somewhat for 
getting snow development...so did end up going with categorical probability of precipitation 
for most of northestern 2/3 of area...and likely elsewhere. After some 
deliberation...with the distinct break of significant precipitation 
this morning...and likelihood that most remaining precipitation will end up 
snow...and only an inch or two at most...decided to discontinue the 
ongoing Winter Weather Advisory. 


Otherwise...did give some consideration to a wind highlight today. 
Strong pressure rises currently across eastern Montana on order of 7hpa/3h 
will build southward...but find that strongest surge will progress through Western 
Plains. Gradient winds are not as strong farther ewrd as a result of 
the upper circulation/frontal location...and best surge with potential 
to get advisory winds would brush far southwestern 3 counties at best. Held off 
on issuing a Wind Advisory...but do have winds up against the lower end 
of threshold by midday and through afternoon. Farther east...winds will also 
certainly increase...but slightly weaker gradient toward the east 
should keep blowing snow from being a widespread issue...another 
factor in not continuing winter weather highlight. Temperatures today will 
certainly reach highs fairly early in the day...with more notable 
drop coming during the afternoon hours. 


For tonight into Saturday...strong surface ridge will build quickly 
sewrd and shift off to the southeast...allowing westerly gradient to 
develop and moderate temperatures fairly quickly...esply far west. Depending on 
how thick increase in clouds is later Sat into Sat night...temperatures 
may be very elevation dependent as the gradient drops off with weak 
trough/warm front sliding in...keeping a push of slightly warmer air 
aloft. However...strong wave digging southeast may kick a weak reinforcement 
of colder air into eastern County Warning Area by Sunday. For the time...kept precipitation 
free...but some indication that strong divergence q digging from northestern South Dakota into 
southern Minnesota may yet be able to saturate up enough to develop light precipitation 
across northestern County Warning Area. 


Next strong precipitation indication comes in around Sun night. Guidance has 
been fairly consistent with very strong wave pushing quickly southeast through 
area...with some minor differences in timing. Very strong thermal 
ribbon will be in place to interact...and kicked probability of precipitation up toward likely 
across northestern 1/2 of County Warning Area following consensus upper forcing. 
Again...locating the main frontogenetic banding at this range the 
only thing keeping from categorical probability of precipitation. This snowfall will be 
coincident with the strong warm air advection zone...ahead of impressive Arctic 
front which will kill the temperature rise early on Monday by all 
indications. Will keep chance probability of precipitation working with strong low level 
baroclinic zone...surging southward behind clipper. Timing consensus is 
not the strong suit of the last few operational sets by Middle Range 
with GFS continuing to trend toward the fast side of both the 
superensemble and its own ensemble set. Therefore...probability of precipitation for Tuesday 
system are not as high as probably should be...with precipitation almost a 
certainty within a 24h period. This cold intrusion will make 
Monday/Monday night anything but a pleasant time...with wind chills. 
However...this cold push is but the tip of The Iceberg...as stronger 
push coming into focus for middle to late week. Several of the model 
predicted fields correspond to patterns in local extreme event 
climatology for coldest maximum temperatures for middle January. 


&& 


Aviation... 
an upper wave will drop through the area this afternoon as the 800 
mb front is moving through. These two features should interact to 
produce light snow across the area...beginning around Highway 14 in 
Hon...bkx and mml and then spreading southeast through the day. As a 
result MVFR ceilings and visibilities can be expected. There will likely be a 
period where visibilities will fall below 3sm north of a khon to kfsd to kslb 
line. To the southwest...the frontal lift does not appear as 
organized and there is a decreased likelihood of IFR conditions 
although MVFR conditions are anticipated. Ceilings should improve 
overnight from north to south with most locations clear by 12z 
Saturday. Winds will also increase out of the north during the day and 
be strong along and west of the James River. Winds will diminish 
after sunset across the region as high pressure moves into the area. 


&& 


Fsd watches/warnings/advisories... 
Iowa...none. 
Minnesota...none. 
NE...none. 
South Dakota...none. 


&& 


$$ 


Chapman/schumacher