Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 201728

Area Forecast Discussion
National Weather Service Sioux Falls SD
1228 PM CDT Tue Mar 20 2018

.SHORT TERM...(Today and Tonight)
Issued at 417 AM CDT Tue Mar 20 2018

Light precipitation will be the primary concern through tonight,
especially during the morning/early afternoon. Mid-upper level wave
currently tracking across the eastern Dakotas, producing a broad
area of light snow which has been progressing slowly east through
these early morning hours. Progression has been a little slower than
expected, as we continue to fight a layer of dry air advecting into
our far eastern counties. Persistent weak lift should be able to
overcome that by daybreak though, so will continue to carry high
pops across our eastern areas through late morning, then gradually
taper them off as the wave passes by this afternoon. Based on web
cam images and reports thus far which indicate the light snow has
had trouble accumulating, especially on non-grassy areas, so have
lowered our snow-liquid ratios below 10:1 most areas. This will cut
back overall snow totals to less than 2 inches across the forecast
area, including daytime snow amounts from around an inch in our far
eastern areas, to just a tenth or two toward the I-29 corridor after

Mid levels dry out again behind the morning wave, but we still have
another subtle wave forecast to drop southeast across the eastern
Dakotas tonight. NAM/Canadian producing spotty QPF with this wave,
which would most likely be drizzle given the lack of saturation in
that ice-producing layer. As temperatures dip back below freezing
tonight, could see spotty freezing drizzle if it materializes at
all. However, given the warm days and relatively mild nighttime
lows, road temps have been warming well above freezing during the
day and not dropping too far below freezing at night. Thus think
impact of any freezing precip will be minimal, but will mention
potential for light icing on untreated surfaces in the HWO.

.LONG TERM...(Wednesday through Monday)
Issued at 417 AM CDT Tue Mar 20 2018

Upper ridge builds into the Plains midweek, providing quiet weather
and warming temperatures for Wednesday through Thursday. Expect to
see temperatures warm into the upper 30s and 40s on Wednesday, with
readings 4-8 degrees warmer on Thursday.

A couple of systems slated to affect region late week through the
upcoming weekend. The first will be a broad wave lifting northeast
along the western side of the upper ridge Thursday night/Friday.
Expect much of the area to see rain with this wave, with exception
begin areas northeast of KBKX-KSPW line, where thermal profiles may
cool enough to support some light snow late Thursday night/Friday
morning. Any snowfall amounts expected to be minimal at this time.

A stronger wave ejects out of the Rockies and deepens as it moves
across the northern/central Plains later Friday night/Saturday.
GFS/ECMWF appear similar with the timing/track of the wave at this
time, but thermal profiles still differ, with GFS currently warmer
than the ECMWF, which is also on the cooler side of its ensemble
temperature spread. As such, still quite a bit of uncertainty in
this regard, so did not deviate from broad model consensus much.
Even with the cooler solutions, appears that most of our forecast
would be on the warmer side with minimal snow potential. Exception
again would be in southwest Minnesota and possibly Iowa Great Lakes,
but far too early to determine potential snow amounts given the high
degree of uncertainty.

Generally unsettled pattern continues into early next week, but
models are showing very little agreement in placement/timing of any
key features beyond Saturday, so confidence in any rain/snow chances
are low for that range.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1210 PM CDT Tue Mar 20 2018

Back edge of the light snow is right along the the I-29 corridor
as of 17z and will continue to taper off from west to east thru
the early afternoon hours across SW MN and NW IA. Chance of some
patchy light drizzle or freezing drizzle mainly to the north and
east of KFSD this evening. Could also see some patchy fog early
Wednesday, but confidence in its extent or impact on a specific
TAF site is too low to include as of now. Otherwise, look for
IFR/MVFR stratus to continue through the overnight hours before
conditions improve through the day on Wednesday.




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