Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 141958

Area Forecast Discussion
National Weather Service Sioux Falls SD
258 PM CDT Wed Mar 14 2018

.SHORT TERM...(This evening through Thursday)
Issued at 258 PM CDT Wed Mar 14 2018

Cool high pressure will settle into the area tonight and allow for
some cooler readings as winds remain light into the night. Will have
to keep an eye out for stratus potential over southwest MN and east
central SD late tonight and early Thursday morning, but for now
confidence too low to have in forecast. Lows in the teens near
highway 14 and 20 to 25 elsewhere.

Easterly flow will gradually increase on Thursday, bordering on
breezy by late afternoon and evening. Otherwise a decent amount of
sunshine will allow temperatures to climb to near 50 along the
Missouri River and generally upper 30s to mid 40s elsewhere.

.LONG TERM...(Thursday night through Wednesday)
Issued at 258 PM CDT Wed Mar 14 2018

On Thursday night low pressure aloft will deepen across western
Nebraska, then gradually shift east and slightly northeast into
Friday. This will bring a deep easterly flow with just a bit of a
northerly component. This interaction with the increasing moisture
from the south and the drier easterly flow from Minnesota and
northern IA should set a fairly distinct northern edge to the
precipitation shield. The extent of this warm/moist advection
northward will be very dependent upon whether or not the upper level
wave wobbles north and by how much. So, for now will keep the better
chances south of Interstate 90 with the thought that the drying flow
will eat into the precipitation potential. The better chance for
precipitation will be from late Thursday night into Friday evening.

One trend to watch however is drying aloft and losing saturation in
the ice bearing layer, which might bring more of a chance for
drizzle or light freezing drizzle. So, precipitation type will be a
challenge as the wave allows for just a bit of a southerly component
to the wind field in the 850mb to 700mb layer. This will aid in
delivering some warmer and moist air over the top of the cooler near
surface colder air mass. Because temperatures in this layer are
expected to be a touch above freezing some sleet will be possible.
Once the forcing increases enough on Friday morning the main
precipitation type should be snowfall, but as stated above if
saturation is lost the main precipitation type will be drizzle. At
this time it appears there will be a threat for about 2 to 4 inches
of snow from north of the Missouri River to just south of highway
14. The better chance for freezing drizzle/sleet should be south of
Interstate 90. If the models continue the trends seen in this run
then there will likely be a need for a winter weather advisory for
Friday at some point in time.

Flow behind this system will remain easterly into Saturday, then
become light Sunday before becoming east again on Sunday night as
the next system approaches. This suggests that Friday and possibly
most of Saturday could get stuck in low cloud cover. Therefore
nighttime lows may be above average in the lower to mid 20s while
highs will be below normal in the mid 30s.

The next system of interest moves onto the Plains on Sunday night
into Monday. Temperatures aloft for this system suggest that the
surface temperatures will be the main determinant for precipitation
type, which should be either rain or snow.

Beyond this the models do not have much in the way of agreement but
overall should see temperatures below normal with a continued threat
for precipitation.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1159 AM CDT Wed Mar 14 2018

VFR through about 8z tonight. Cooler air will drop southwest from
MN and MVFR ceilings will become likely. The better chances for
MVFR ceilings will be far east SD and southwest MN and from about
8z through 16z Thursday.




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