393
FXUS63 KFSD 170507
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1107 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1107 PM CST Tue Dec 16 2025

VFR ceilings expected for most of the period. Short term guidance
has backed off somewhat on the development of patchy dense fog.
However, model soundings indicate strong inversions developing,
which would work to trap moisture near the surface, gradually
saturating and resulting in fog. Have backed off on widespread MVFR
visibility, but confidence is high enough to leave it in the TAFs
for now at all three sites. The potential for pockets of dense fog
remain, with rapid decreases in visibility to 3 miles or less
possible. Fog burns off by mid-morning and visibility improves to
VFR.

Winds are light at around 10 kts and are expected to become light
and variable. By daybreak winds will be southerly and begin to
increase. By late morning areas at elevation along the Buffalo Ridge
and those free from snow in central South Dakota will begin to mix
into the strong LLJ. Gusts of 30-40 kts will be common with gusts to
45+ kts possible in south central South Dakota. As the day
continues, and the remaining areas begin to mix deeper, the strong
gusts will overspread the entire region. Strong gusts are expected
to continue through the end of the period. In addition to gusty
winds, strong LLWS between 40-50+ kts is expected to develop by late
morning for areas west of the James River Valley. LLWS expands in
coverage encompassing the whole CWA by afternoon and is
expected to continue through the end of the period.

&&

.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...AJP