Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 180443
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1043 PM CST Wed Jan 17 2018

.SHORT TERM...(This evening through Thursday)
Issued at 300 PM CST Wed Jan 17 2018

Quiet weather in the short-term. Continued westerly flow over the
next 24 h will continue to bring warmer air into the area. While the
flow is not perpendicular to the Buffalo Ridge, there is a strong
enough cross-ridge component as well as strong thermal inversion to
keep wind gusting over 20 mph through Thursday. Winds will become
lighter - especially in valley locations - later tonight. This will
allow low temperatures to fall into the teens. On Thursday, 925 mb
temperatures will range from 3 to 10 C. While there is some snow on
the ground, its impact will not real significant - maybe keep
temperatures 3 to 5 degrees cooler than if it fully mixed out. For
this reason, have raised highs into the 40s everywhere with the
lower 50s in south central South Dakota.

.LONG TERM...(Thursday night through Wednesday)
Issued at 300 PM CST Wed Jan 17 2018

The primary focus in the long term is the warm weather on Friday
and the potential winter storm for later Sunday into Monday.

On Friday, a weak boundary is forecast to move slowly southward
through the area. Ahead of the boundary 925 mb temps are around 10 C
and they only slowly cool behind the boundary. At least some of the
area will lose snowcover tomorrow so that mixing could be more
efficient. Based upon current satellite picture that seems most
likely west of the James River and also in the Missouri Valley.
However, there could also be more cirrus around which would limit
solar heating. For this reason, limited mixing to around 3 C above
925 mb temperatures. That still results in high temperatures warmer
than Thursday from the mid 40s along the Buffalo Ridge to the mid
50s in the Missouri Valley.

No significant cooling is expected behind the front as lows will
remain in the 20s on Friday night. Despite more clouds and
northeasterly, temperatures are expected to remain above seasonal
normals from the upper 30s in southwestern Minnesota to the mid 40s
around Yankton and Sioux City.

A more significant system may impact the area Sunday and Monday.
Initially, we are expecting a 700 mb front to set up over the
northern Plains and interact with the entrance region of an upper
level jet near the Canadian border. The exact location of the front
remains very uncertain at this time but the most likely area would
be north of I90 and it could even be north of Hwy 14. This would
bring light snow from late Saturday night into Sunday. A more
significant upper low is then expected to move northeast from the
Rockies into the Great Lakes. Model solutions are becoming more
certain that this will impact the central Plains into the Great
Lakes and could bring significant snowfall with strong winds.

Both timing and location remain highly uncertain. In terms of
timing, snowfall could occur anytime from Sunday afternoon into
Monday evening. Currently the GFS is the fastest solution - starting
Sunday afternoon and ending sometime Monday morning while the ECMWF
and Canadian have the heaviest snowfall on Monday morning ending
Monday evening. The location is still varying from central and
northern Iowa to as far north as northeastern South Dakota and
central Minnesota. What we can say is confidence has increased that
many areas will see at least light snowfall sometime from late
Sunday afternoon into Monday morning. However, whether any one
location will see heavy snowfall remains very uncertain. So,
although both the 12Z GFS and ECMWF do show heavy snow for the tri-
state area, do not focus on the exact location or amounts from any
one model. Instead, be aware that a winter storm is possible but
areas that could be affected could still be south of Sioux City and
Spencer or north of Chamberlain, Brookings and Marshall. It remains
too early to say with any confidence if any one location will be
impacted.

Following the system on Sunday and Monday - near normal temperatures
are expected into the middle of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1042 PM CST Wed Jan 17 2018

VFR conditions are expected through the TAF period.

&&

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

$$

SHORT TERM...Schumacher
LONG TERM...Schumacher
AVIATION...



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