Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 212307
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
607 PM CDT Tue Mar 21 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM CDT Tue Mar 21 2017

Dry air continues to filter into the area from the northeast with
mid level moisture streaming overhead. This will be the challenge
through the night as dry air and decreasing winds will set up the
potential for some pretty chilly morning low temperatures. But, with
mid level moisture increasing ahead of a weak wave and winds turning
normal to the mid level thermal band some snowfall will be possible
late tonight and Wednesday morning into the early afternoon. Chances
are marginal with very dry air in the low levels fighting any
forcing and saturation aloft. It appears that the best combination
of low level moisture and forcing is late tonight and Wednesday
morning along and west of the James River Valley. As the boundary
shifts northeast the precipitation potential should dwindle as dry
air becomes increasingly difficult to overcome. Regardless, looking
at an inch or so in areas more favorable for snow with lesser
amounts along and east of Interstate 29. Tonight into tomorrow will
be continued chilly with lows in the 20s and highs in the 30s, a few
40s along and west of the James River.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CDT Tue Mar 21 2017

Wednesday night should be pretty quiet with a small chance for
precipitation along and west of the Missouri River late at night.
Strong southerly flow will help keep temperatures mild at night with
30s for lows.

Thursday will see the deeper moisture and more significant warm air
advection set up. This will bring an increasing chance for rain, but
some fairly dry mid level air may set up a bit of a cap making
saturation difficult as well as not being able to take advantage of
any elevated instability if any does exist.

The main challenges Thursday night into Friday night will be
instability and moisture. The models have trended just a bit south
with precipitation and one of the factors is a bit of a loss of mid
level moisture. The dendritic layer is fairly high for this time of
the year, residing somewhere close to 550mb, and once some dry air
begins to work into that layer we will need to rely upon instability
to bring a precipitation threat. Right now areas about northwest of
a Chamberlain to Marshall MN line may struggle with a lack of mid
level moisture and a lack of instability. This would likely then
support widespread low clouds, the low levels do not appear to have
any issues with moisture, but little in the way of precipitation
amounts. Will not make any major changes to the forecast as this
could very well trend back to the north, or possibly farther south.
A little too early to really tell. Right now area along and south of
a Tyndall to Jackson MN line still appear to be in very good
position to receive widespread precipitation with a combination of
weak instability and more persistent mid level saturation. These are
the areas with the best chance for 1 to 2 inches of rainfall as well
as a little thunder and lightning. And, at least for now, rain
appears to be the main threat with this system. Soundings are far
too warm during the strongest forcing to support anything even close
to snow.

While precipitation may linger into Saturday morning the upper low
will be shifting east and taking the lift with it.

The environment left behind as the low exits will be cool, but not
real dry so we will likely be dealing with cloud cover issues Sunday
through Tuesday. The models are also consistent and persistent with
the west southwest flow aloft which favors bringing any upper level
waves into the Central Plains and bringing continued shots of
precipitation through at least the middle of next week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 603 PM CDT Tue Mar 21 2017

VFR conditions expected through tonight, then a band of light
snow will lift across the area by Wednesday morning. This could
result in brief reductions to MVFR conditions. Southeasterly winds
will pick up on Wednesday morning, gusting to around 25 kts into
the afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...JM


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