600
FXUS63 KFSD 172015
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
215 PM CST Mon Nov 17 2025

.KEY MESSAGES...

- Rain changes increase rapidly into the evening hours.
  Scattered lightning strikes may be observed into mid-evening.

- Rain will begin to transition to a wintry mix and then to all
  snow over portions of SW Minnesota and eastern South Dakota
  after midnight.

- Snow accumulations remain dependent on ground/road
  temperatures but moreso snow rate. General consensus of 1-4"
  may be possible in a very narrow corridor by Tuesday mid-
  morning, 40% probability of a higher amount than 4" over
  Lincoln and Lyon counties.

- A quiet remainder of the work week is expected and likely
  continues through next weekend. Temperatures will be near
  normal (mid 40 highs to mid 20s lows).

&&

.DISCUSSION...
Issued at 208 PM CST Mon Nov 17 2025

THIS AFTERNOON: Compact upper low beginning to move out of the
Central Rockies and into the Central Plains early this afternoon.
Ahead of this wave, we`re already seeing a narrow corridor of warm
advection showers develop.  A slight bit of instability (100-300
J/KG) has also led to scattered lightning strikes at times and is
also indicative of the dynamic nature of this system. Temperatures
have risen into the upper 40s to lower 50s, but will begin to stall
or lower as rain moves northeast due to evaporative cooling.

THIS EVENING: We`ll continue to see broad expansion of showers
through the late afternoon and evening hours as the upper low
moves across Nebraska. Persistent warm advection below a broad
area of dPVA and upper divergence will lead to expansive
coverage of light to occasionally moderate rain showers. A few
additional thunderstorms may redevelop along NE Nebraska and NW
Iowa by mid- evening on the edge of stronger vorticity advection
and 50-100 J/KG MUCAPE. Temperatures will continue to see a
steady drop this evening as drier air moving in from the
northeast effectively wet-bulbs temperatures to the 30s.

TONIGHT:  Greatest concerns tonight are focused on the eventual
development of an elongated band of channeled mid-lvl frontogenesis
within a broad deformation band that will develop over eastern SODAK
and spread east through west central and southeastern Minnesota.
While temperatures early in the evening will slowly fall into the
mid-30s in these areas, a reasonable setup for dynamical cooling
(and persistent evaporative cooling) should develop, leading to
the overall atmospheric column running near to just slightly
below freezing at times. Most CAMS and lower resolution guidance
supports a change over to rain/sleet along the higher elevation
areas of the ridge by 03z, with potential for a complete
changeover to snow by 06Z beginning in a broader area along the
enhanced forcing. Then the questions turn into...

1. Where does this narrow precip band stall?  Mid-day models suggest
an area either side Highway 14 extending down along the Minnesota
River Valley.

2. What impact will ground/road temperatures have on accumulation?
Most observations indicate these temperatures remain in the 40s to
near 50.  This could really limit road snow accumulations outside of
strong rates.

3. What are the snow rates/ratios:  In most areas marginal
temperatures may hold down rates to lead to less accumulations.
However wherever this band develops, potential for 10:1 rates
could overwhelm warm ground. HREF guidance indicates 30%
potential for 1" hour totals briefly, and HRRR guidance also
indicates brief windows for 0.5-1.5" totals. This afternoon`s
release of instability also shows a more dynamic system than
models are catching onto, which would further support higher
HREF rate suggestions.

All this said...deterministic models indicate potential for 1-4"
totals (elevation dependent) with ensembles supporting similar
numbers. HREF probabilistic numbers indicate 25/75th data of
2-6" but this is influenced by static 10:1 event ratios. With
all this in mind, after significant adjustments to both
probabilistic input to temperatures and p-type, will issue a
narrow advisory from Hwy 14 along the Ridge in SW Minnesota. If
the band of snow sets up further north/south or changeover
develops earlier to the SW, the advisory may need to be adjusted
by mid-evening.

Further southwest, the low track over northern Nebraska will
keep most of the area into an area of significant low-lvl
saturation, but a lack of deep saturation. The end result will
be persistent showers to drizzle at times through daybreak and
temperatures well above freezing.

TUESDAY:  Precipitation gradually ends Tuesday morning with drier
air filtering southeast through the day. Temperatures remain
slightly below normal in most areas, and may be stalled in areas
where fresh snow falls.

WEDNESDAY-SUNDAY: A VERY quiet medium and extended range forecast is
expected through the rest of this week and through next weekend.
Outside of a weak surface trough passing through the area late
Wednesday and again Friday (only which the Wednesday trough brings a
risk of sprinkles) , most of the week will be dominated by high
pressure. No sharp rises or drops in temperatures are anticipated at
this time, with temperatures at times a couple degrees below or
above normal.


&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1115 AM CST Mon Nov 17 2025

Ceilings will continue to lower through the afternoon as a band
of showers develops and lifts northward through the Tri-State
area.

Initially MVFR ceilings with widespread showers area likely in
most areas into the overnight hours. Gradually cooling aloft
will lead to sleet or even snow to develop by midnight along the
higher ridge elevations. Further southwest, showers may turn
into drizzle and lower IFR ceilings into daybreak Tuesday. Light
snow may persist in SW Minnesota and adjacent areas of SD into
mid-morning Tuesday.

The passages of surface low pressure will turn winds from an
east southeast direction this afternoon towards the northeast
and north by daybreak Tuesday.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from midnight tonight to 9 AM CST
     Tuesday for SDZ040.
MN...Winter Weather Advisory from midnight tonight to 9 AM CST
     Tuesday for MNZ071-072-080-081-097.
IA...None.
NE...None.

&&

$$

DISCUSSION...Dux
AVIATION...Dux