116
FXUS63 KFSD 162009
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
209 PM CST Tue Dec 16 2025

.KEY MESSAGES...

- Uncertainty lingers on fog potential into Wednesday morning.
  Snow melt fog may turn dense at times, favored along or east
  of I-29 into mid-morning.

- Strong southwest winds will develop Wednesday afternoon. Peak
  winds may exceed advisory criteria especially in higher
  elevations, but this could expand elsewhere.

- Strong front arrives Thursday morning bringing high winds and
  increasing snow risks. A high wind watch has been issued for
  most areas, given moderate to high confidence.

- Potential for snow squalls remains at daybreak Thursday, with
  impacts to visibility/travel possible into the afternoon due
  to continuing snow showers.

- Mild temperatures and mostly dry conditions are then expected
  into next weekend and the first portions of Christmas week.

&&

.DISCUSSION...
Issued at 204 PM CST Tue Dec 16 2025

THIS AFTERNOON: Temperatures are quickly rising through the 40s and
into the 50s in many areas this afternoon.  Snow-free areas of south
central South Dakota are even experiencing temperatures in the 60s.
Breezy westerly winds will continue to push this warmer air
eastward before quickly diminishing after sunset.

TONIGHT:  Weak mid-lvl wave will pass through the region this
evening.  While ceilings remain very high, a sprinkle or two may be
possible south of I-90.  Otherwise, we`ll be watching the diurnal
fall in temperatures through the evening. This thermal drop, when
combined with light winds and snow melt, may lead to period of fog
developing over the overnight hours.  Aviation guidance remains
split, with a handful of models showing the impact of thick cirrus
holding temperatures higher, and others showing the quick drop and
trapping of boundary layer moisture below a steepening inversion. If
fog does form, it may become dense with advisories possible into mid-
morning.

WEDNESDAY:  Strong warm advection streams through the Plains on
Wednesday, as mid-lvl vorticity begins to cross the Rockies.  A
seasonally strong LLJ develops through the day on Wednesday, with
850mb winds sitting outside the 30 year climatology. As mixing
increases, potential for strong winds also increases.  First, will
be snow-free or higher elevation terrain areas of the Buffalo Ridge
and South Central SD Missouri River valley areas where 50+ mph winds
may be possible.  The greater questions will be found elsewhere,
where the impact of lingering snow may have the potential to reduce
potential wind gusts.  For now, will issue an advisory for areas
previously mentioned, and allow later shifts to gain a better idea
of how overall winds may mix downward Wednesday afternoon. The
strong winds over snow-free areas may lead to elevated fire
danger.

WEDNESDAY NIGHT:  Scattered showers may begin to develop Wednesday
evening as mid-lvl vorticity tracks eastward, with much higher
precipitation chances forming late Wednesday evening and into the
overnight hours along the passage of an 850 mb boundary.
Thankfully temperatures remain well above freezing, so only
expecting rain at this point. Temperatures will not fall
significantly by Thursday morning, and will continuing using a
non-standard diurnal curve.

THURSDAY: A deepening upper low crossing the Dakotas will push a
sharp low-lvl front southeast through South Dakota at daybreak.
Rapid cold advection will lead to 9-10C/KM lapse rates during the
passage of this front.  Combine these lapse rates with weak
instability, and a very tight SPG formation and the potential for a
narrow band of snow squalls may be possible.  Most medium range
guidance is showing a narrow elevated band of increased snow
squall parameter numbers with the passage of the front.
Additional scattered snow showers will develop through the
morning and into early afternoon as the upper low pivots through
the Minnesota River valley. Overall accumulations will not be
that significant, with a dusting to half inch in most areas.

A strong concern for Thursday will be winds. After the daybreak
front passes southeast, guidance is in strong agreement that another
seasonally strong 850mb wind field will spread southeast in the day.
ESAT tables from the NAEFS/ECE both suggest yet another
climatologically significant wind event. The biggest question
is where the strongest corridor of winds will fall. NAM/GFS are
both a bit more to the southwest of the other camp of EC/CMC
pulling 50 to 60+ mph winds through mostly the James River
valley and areas southwest. The other solutions are more broad
with a larger area of high winds spreading throughout the Tri-
State area. ATTM, confidence is high enough to issue a high wind
watch for most of the Tri-state area for Thursday.

IMPACT:  Outside of the impacts from high winds, the potential
combination of strong winds and falling snow Thursday morning and
early afternoon post the greatest concern.  Thankfully several warm
days will stabilize the existing snowpack, reducing the potential
for any significant lofting of old snow.  However, the potential for
either early snow squalls and/or HCR snow bands within a deep and
favorable DGZ mid/late morning pose the risks for both visibility
and travel impacts.  Early looks at the HREF guidance for Thursday
morning does support 30 to 50% probabilities for 0.5 mile
visibility and 35+ mph winds. For now, confidence is NOT high
enough for any winter storm watches, but this event may have to
be monitored closely.

FRIDAY ONWARD:  Confidence remains high that we`re headed towards a
warmer zonal flow pattern into the weekend and into early next week.
Generally a fairly quiet pattern to be in, it will feature more days
above normal than below normal, with occasionally strong
southwesterly gusts.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1111 AM CST Tue Dec 16 2025

VFR conditions continue through the daytime hours of Tuesday.
We`ll begin to see weak winds potentially lead to fog formation
overnight and into Wednesday morning. Some uncertainty continues
on just how low visibility may fall, but potentially may see
dense fog at times.

Winds increase through Wednesday morning, with strong gusty
south winds likely by Wednesday afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Watch from Thursday morning through Thursday
     afternoon for SDZ039-040-054>056-060>062-065>071.
     Wind Advisory from noon to 6 PM CST Wednesday for SDZ040-050-
     057-063.
     High Wind Watch from late Wednesday night through Thursday
     afternoon for SDZ038-050-052-053-057>059-063-064.
MN...High Wind Watch from Thursday morning through Thursday
     afternoon for MNZ071-072-080-081-089-097-098.
     Wind Advisory from noon to 6 PM CST Wednesday for MNZ071-072-
     080-081-090.
IA...High Wind Watch from Thursday morning through Thursday
     afternoon for IAZ001-012.
     High Wind Watch from Thursday morning through Thursday
     afternoon for IAZ020-031.
NE...High Wind Watch from Thursday morning through Thursday
     afternoon for NEZ013-014.

&&

$$

DISCUSSION...Dux
AVIATION...Dux