Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 070432
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1032 PM CST Tue Dec 6 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 303 PM CST Tue Dec 6 2016

The big news for tonight and Wednesday will still be the winds and
cold. Winds should taper off tonight, only slowly, but they should
decrease below wind advisory levels by 9pm. Will let the advisory
from Interstate 90 north and down to Spencer IA continue to that
time for now, then as early evening approaches we can take another
look for possible earlier ending.

Temperatures will also decrease slowly, to low readings tonight a
little above guidance. Wind chills will drop to below zero
everywhere, and to double digits below in parts of the area north of
Interstate 90. They will not reach wind chill advisory levels, so
will not issue that product, although that does not mean some danger
will not be there on this first decent cold shot of the winter.

It will be windy again Wednesday with a good gradient continuing.
However, with a shallower mixing layer than today indicated on model
soundings, it will be somewhat less windy. Still, had to push up
model blend winds.

As the mixing subsides this evening, and low level moisture pulls
further north a little, any lingering flurries should end. Will
carry a few into the early evening. A little resurgence of this
moisture is expected Wednesday as a weak lobe rotates around the
back end of the receding Ontario upper low, and what moisture there
is will again be in the low dendritic layer, so expect a few
flurries mainly north of Interstate 90. In such a pattern, some of
these flurries will likely be sparkling in some sunshine as they
blow around. Do not expect any measurable snow.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 303 PM CST Tue Dec 6 2016

Saturday into Saturday night will see a fairly strong wave swing
quickly through the area. Ahead of this wave on Friday mid level
thermal banding will lift north and a small band of light snow will
be possible Friday afternoon and night north of Interstate 90 but at
this time it does not look real probable. What this thermal banding
lifting to the north does however is create a less efficient snow
making system for Saturday and Saturday night as the deeper
dendritic layer is north of interstate 90 into central MN. Southwest
MN should see the better chance for measurable snow with the threat
tapering off to the southwest. At this time would lean towards the
potential for a couple of inches in southwest MN.

Temperatures will be stuck in the teens and maybe lower 20s for
highs Thursday and Friday but with the approach of the system for
Saturday temperatures will likely climb back into the 20s to lower
30s in most locations.

No easy answers in the outer periods of Sunday through Tuesday with
the arctic boundary nearby and a series of weaker waves causing it
to wobble north to south from time to time. Needless to say these
waves are not timed the same from model to model and run to run so
confidence on which days will be really cold and which days will be
kinda cold not possible right now. Ensembles not very helpful as
well with 6 to 7 standard deviations showing up on Monday and
Tuesday. So, at this time will not stray far from guidance but if we
can get some snow cover over the weekend the confidence in the
colder temperatures will increase. Will start to watch the Wednesday
through Friday time frame next week as well as the models are more
agreeable on burying the cold air in. Local research shows that
highs and lows are about 10 to 12 degrees colder on average when
there is about 2 inches or more of snow on the ground versus no
snow, so getting or not getting snow over the weekend will make a
big difference since we are sitting with no snow on the ground at
this time. For example in Sioux Falls for the second week of
December the average high is right around 40, but with 2-5 inches of
snow on the ground the average high is only 25.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1028 PM CST Tue Dec 6 2016

Northwesterly winds will continue to gust 20 to 25 kts overnight.
Winds will then pick up a bit on Wednesday morning, gusting to
near 30 kts through the afternoon and evening.

&&

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

$$

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



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