902 
fxus63 kfsd 182015 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
315 PM CDT Thursday Mar 18 2010 


Discussion... 
a series of cold fronts are expected to make their way through the 
forecast area through the late afternoon hours into the overnight. 
The first cold front as of 20z extends from kmwm to kykn. Not much 
in the way of cold air behind this front...however...stronger surge 
of cold air expected tonight. With this surge of cooler air...expect 
winds to increase out of the north and become somewhat gusty. 
Fairly impressive band of frontogenesis moves through the area 
overnight...with the strongest lift centered in the 650-700 mb 
layer. The crux of the upper level pv remains focused south and west 
of the forecast area...and forecast soundings certainly indicate 
some saturation issues in the lowest portions of the atmosphere. 
Think that is doing quite a number on the guidance probability of precipitation which range 
from 10 to 30 percent from northeast to southwest. Have sided much 
higher than the guidance probability of precipitation tonight...especially south of a line 
from khon-kfsd-kslb. Precipitation type is tricky as the colder air surges 
in from aloft...but am expecting rain to mix with and potentually 
change over to snow. Snowfall amounts should be light though...as 
the frontogenesis remains focused immediately ahead of the cold air. 
Could see a brief period on the back edge of the precipitation result in a 
few tenths of an inch of snow...but do not expect much in the way of 
accumulation. With such strong cold air advection...have tweaked 
lows down into the upper 20s and lower 30s across the region. 


The system for Friday continues to trend southward and will still 
continue the chance for rain and snow south with an inch or two of 
snow possible. The main threat does look to be south however. 
Otherwise...a little deeper into the cold air a little faster so 
highs in the middle 30s far south with the far northern County Warning Area possibly 
sneaking into the upper 30s if enough of the cloud cover can scour 
out. Otherwise just a little breezy with cold air advection through 
the day. 


Friday night into Saturday will continue the moderately gusty north 
to northwest winds and chilly temperatures. Lows on Friday night in 
the 20s with highs on Saturday in the 30s again. No chance for 
precipitation during this time. 


The models have come for around for Sunday and are now suggesting a 
milder day than previously forecast. The GFS/Canadian and ec all 
hinting at winds from the west or southwest with 925mb temperatures 
climbing to around +4 east to +8 to 10 central. This would easily 
support upper 40s west and middle to upper 50s central South Dakota...but will 
play down about 4 or 5 degrees below this until confidence a little 
higher. Regardless...a decent chance to sneak in a nice day this 
weekend. 


In the latter periods(mon/thu)...model continuity during this time 
frame not very good so confidence running a little low. 
Overall...looks like a fairly fast westerly flow aloft with mainly 
below normal temperatures through the period. The period starts off 
with a warm front near the County Warning Area...varying widely from model to model 
and run to run. The GFS and European model (ecmwf) are farthest north with this 
feature while the Canadian and GFS ensemble are farther south. Will 
aim for this front to be somewhere over the northern parts of the 
County Warning Area on Monday...then swing through Monday night into Tuesday as a 
relatively weak cold front. Monday does have the potential to near 
or a little above normal if the front can get far enough north to 
allow for a little bit better southerly mixing. After this...Tuesday 
into Wednesday could see some rain or snow potential as the front 
passes but will only carry low probability of precipitation due to lack of confidence in 
timing and strength. Going dry on Thursday. Otherwise...highs mainly 
in the 40s with lows from the 20s into the lower 30s. 


&& 


Aviation... 
VFR conditions will gradually deteriorate as a series of cold fronts 
make their way through the northern plains. As colder air moves 
into the region...north winds will become gusty. Chance of 
precipitation south of a line from khon-kslb...with greatest impact 
on ksux terminal. Expect precipitation to begin as rain...mixing with and 
changing over to snow. Light snow will continue on after 12z on 
Friday in ksux with breezy north winds continuing. 




&& 


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


&& 


$$ 
Bt/08