138
FXUS63 KFSD 270353
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1053 PM CDT Thu Jun 26 2025

.KEY MESSAGES...

- Scattered showers/isolated storms will continue to diminish
  in coverage through this afternoon. Still a low risk for an
  isolated strong/severe storm in our far southeast counties
  this afternoon, but greater threat will be east of Highway 71
  corridor.

- Periodic thunderstorm chances continue Friday evening through
  the weekend. Some indication that storms could become strong
  to severe at times. Begin monitoring this time period if you
  have outdoor plans.

- Warming temperatures and increasing humidity this weekend will
  bring a risk of heat indices above 100F in some areas Saturday
  afternoon. Otherwise seasonably warm temperatures will prevail
  much of next week.

&&

.DISCUSSION...
Issued at 258 PM CDT Thu Jun 26 2025

TONIGHT-FRIDAY: As the slow-moving wave lifts northeast through
the rest of the afternoon, our remaining showers/isolated storms
east of I-29 should continue to push east and diminish prior to
sunset. Limited mixing with broad cloud cover today, combined with
decent rainfall over the past 2-3 days will leave behind abundant
boundary layer moisture. Surface high pressure drifts in tonight,
providing light winds and a general attempt at clearing behind the
departing wave. This could set up a reasonable set-up for some fog
development overnight over a broad expanse of the forecast area,
though some question as to whether dense fog will develop or not.
This would linger just beyond sunrise Friday, but should burn off
pretty quickly.

FRIDAY NIGHT-SUNDAY NIGHT: A more unsettled quasi-zonal flow
pattern sets up for this last weekend of June, with various waves
triggering periodic chances for storms from Friday evening into
Sunday. Given some dependence on the previous day`s activity, the
exact timing/location of storm chances is somewhat uncertain.
However, we could be looking at multiple rounds of strong to
severe storms during this period. Currently Friday evening looks
to be round 1, though some question regarding whether storms
coming out of central SD in the early evening will maintain
strength as they move east of the James River. 12Z HRRR/FV3 had
presented an alternate scenario showing limited early evening
activity with a stronger complex diving southeast out of ND late
evening into the overnight; however, the 18Z HRRR has backed away
from this, instead keeping the stronger ND complex well to our
north. Pockets of damaging wind look to be the primary threat with
storms that may impact the forecast area Friday evening.

How Friday night-early Saturday evolves could play a role in later
Saturday activity and too much uncertainty to pinpoint a preferred
solution at this point. That said, forecast soundings are much
more robust with projected instability with steeper mid-level
lapse rates supporting a greater large hail threat, and dry mid
levels and sub-cloud layers providing a risk for damaging wind.
Main question would be whether storms can maintain some semblance
of organization or be more pulsy as deep layer shear is on the
weaker side.

Transition to a broad mid-upper level trough takes place Sunday,
which would drag a cool front southeast into the area. Could see
isolated stronger storms develop along this boundary, though its
timing is in question with little model agreement at this range.

Compared to today, the coming days will see a return of warmer and
more humid air, with highs in the 80s most days, briefly pushing
into the 90s on Saturday. Combined with dew points in the 70s,
this could produce some areas of triple-digit heat indices by
Saturday afternoon, so may have to monitor for possible heat
headlines.

MONDAY-THURSDAY: Early-mid week could see some modest mid-upper
level ridging build into the area, but currently not seeing any
signs that significant heat will return. Instead, temperatures
look to be near to slightly above normal as we head into July next
week. Spotty rain chances may accompany any weak waves that move
through the area, but confidence is low in pinpointing any timing
or location.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1049 PM CDT Thu Jun 26 2025

The greatest forecast uncertainty this period will be how thick the
fog can get Friday morning. The LIFR to IFR fog potential will be
dependent on how much of the stratus deck at the start of the period
can erode. More erosion, the better chance of dense fog development.
The less erosion, the lower the chance of dense fog development.
Currently have enough confidence to include LIFR visibilities for
KHON, with the best chance of dense fog development overall in
south-central South Dakota into far southeast South Dakota. Any
fog should lift by 14-15Z and then conditions after that will
quickly become VFR. Some cumulus could form around 8-10 kft in
the afternoon Friday, but otherwise skies will be mainly clear.

High clouds will thicken towards the evening as storms develop to
our west. These storms will likely enter the area from central South
Dakota between 00 and 03Z. If any spot would be impacted by storms
during the last few hours of the period, it would be KHON. However,
there is still a great deal of uncertainty in where storms will go
and thus have left out any mention of TS in the TAFs. Winds will be
light and variable tonight, picking up out of the east-southeast
through the day on Friday. Strongest wind gusts (20-25 kts) Friday
afternoon will be west of the James River, with wind decreasing with
eastward extent.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...Samet