745
FXUS63 KFSD 161042
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
542 AM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Surge of stronger wind gusts 45 to 55 mph behind an outflow
  boundary could impact areas west of a Huron to Mitchell to Lake
  Andes line early this morning. A Wind Advisory has been issued
  for these areas through 10 AM.

- Severe risk today peaks in the late afternoon to mid evening
  east of Highway 81. Large hail to 2" and wind gusts to 70 mph
  are the primary threats, but a tornado is possible.

- Additional storms may move into south central South Dakota and
  through areas south of I-90 tonight into Tuesday morning. A few
  severe storms are possible, but the greater threat may be heavy
  rain and flash flooding in prone areas during this time.

- Very warm temperatures (highs in the 90s) become more likely
  late this week through the weekend, with a moderate to high
  (50-80%) probability of heat indices topping 100F in some areas,
  especially Friday and Saturday.

&&

.UPDATE...
Issued at 539 AM CDT Mon Jun 16 2025

The anticipated heat burst winds from dying thunderstorms in south
central South Dakota have weakened. However, thunderstorms to our
north have been pushing an impressive outflow boundary southward
through central South Dakota early this morning. Gusts behind this
boundary have consistently reached 40+kt with isolated DOT/RWIS
sensors topping 50kt. While the boundary and associated winds are
expected to gradually weaken as it progresses south-southeast, see
decent potential for at least a brief period of advisory level
gusts pushing into our western counties. As such, have issued a
Wind Advisory along/west of Huron-Mitchell-Lake Andes through 10AM
this morning. If gusts weaken more quickly than expected, the Wind
Advisory may be cancelled early.

&&

.DISCUSSION...
Issued at 410 AM CDT Mon Jun 16 2025

Main focus for this forecast cycle is on convective chances and
severe weather risks over the next 24-36 hours or so.

As anticipated, line of severe storms over western South Dakota
late last evening has been weakening as it moves through central
South Dakota over the past few hours. However, occasionally strong
to severe-level wind gusts have been seen upstream from our CWA as
the dying storms produced a progressive heat burst. Could see a
few stronger gusts advancing into our far southwest counties as
the remnants of this line move in, and have issued a Special
Weather Statement to highlight the potential for 50-55 mph gusts
through 5 AM.

The remainder of the morning, the focus for strong to severe
storms should remain well to our north with the MCS currently
rolling through northern SD/southern ND. However, a subtle wave
farther south associated with the dying convective line may spark
a few storms as it moves east into southeast South Dakota through
mid-late morning. The severe risk with this feature appears low,
but if storms do develop, cannot rule out a pulsy storm producing
marginally severe hail/wind.

Attention then turns to greater potential severe risk which is
expected to develop this afternoon. A stout outflow boundary from
the convection to our northwest is progressing southeast, and one
significant question for this afternoon will be how far southeast
does that advance? On top of that, will it be a player in either
enhancing or disrupting/delaying our afternoon storm development?
Unfortunately, the CAMs are not showing a tremendous amount of
agreement on the first question, but those that do maintain some
reflection of the outflow progressing well into our CWA indicate
it may simply serve to delay or refocus initiation a bit farther
east by establishing a cooler boundary layer/stronger cap. With
this in mind, think the favored area for initiation by mid-late
afternoon (3-5 PM) would be near to east of a Yankton to Marshall
line as the stronger wave slides by to our north and drags the
cold front into that area at peak heating. Initial storms should
be discrete with a potential for large hail up to 2" diameter with
isolated gusts to 60 mph, but CAMs are in better agreement that
storms should grow upscale pretty quickly into a bowing line that
could produce gusts to 70 mph and perhaps an isolated embedded
tornado before it exits our eastern counties this evening.

Later tonight, will have to watch for another round of storms
rolling off the High Plains, with lower confidence in whether the
storms will maintain strength as they reach our western counties
in the late evening/early overnight period. Seeing 2 relatively
distinct scenarios with this:

Scenario 1) the storms do hold together and bring at least a
marginal wind threat (low probability given weakening instability
and surface boundary well to our south by then). However, this
scenario would present the greater potential for heavy rainfall
across the southern half of our forecast area late tonight into
early Tuesday.

Scenario 2) the storms weaken much like they have the past couple
of nights as they reach central South Dakota and we see little if
any storm activity overnight.

Erring on the side of caution, will maintain moderate rain chances
across our south tonight, but this is a low confidence forecast.

By later Tuesday, another wave tracks east along the elevated
boundary, bringing some rain chances back to the forecast area.
However, uncertainty in the exact location of the surface and
elevated boundary leads to low confidence in coverage of storms
and associated potential for heavier rainfall and/or isolated
stronger storms.

Broad troughiness and somewhat cooler air lingers midweek with
scattered non-severe storms through Wednesday. Thereafter, we see
a building upper ridge which should limit storm chances by Friday
into the weekend, but this will support highs in the 90s expanding
across the area Friday into the weekend. Ensembles continue to
show potential for triple digit heat indices for some areas with
moderate to high (50-80%) probabilities across southeast SD on
Friday, and over much of the forecast area Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1040 PM CDT Sun Jun 15 2025

Chances will be low for thunderstorm activity overnight, though
some guidance would suggest showers and thunderstorms over
western SD moving eastward into the area late tonight. On
Monday, additional thunderstorms may occur in the afternoon and
evening, though confidence in timing and location is low. If
these storms develop, severe storms are likely. Southerly winds
will become gusty on Monday afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 10 AM CDT this morning for SDZ038-050-052-
     053-057>059-063-064.
MN...None.
IA...None.
NE...None.

&&

$$

UPDATE...JH
DISCUSSION...JH
AVIATION...JM