189
FXUS63 KFSD 200333
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1033 PM CDT Tue Aug 19 2025

.KEY MESSAGES...

- A few spotty showers with an isolated thunderstorm will be
  possible through evening. However, severe weather is not
  expected.

- Areas of fog will build back into areas along and east of
  I-29 tonight. With visibilities of a mile or less possible
  through the morning hours on Wednesday, use extra caution when
  making those morning commutes.

- Shower and thunderstorm chances return by Thursday. While a
  few stronger storms will be possible, some uncertainty still
  remains on the finer details.

- Warm and humid conditions will persist through the midweek
  then fall-like conditions return from the weekend onwards with
  highs likely decrease into the 70s.

&&

.DISCUSSION...
Issued at 210 PM CDT Tue Aug 19 2025

CURRENTS & TONIGHT: Another hot and humid day continues! Taking a
look across the area, warmer conditions persist this afternoon with
most areas sitting in the mid to upper 80s as of 1 pm. Expect highs
to top out in the 80s to low 90s by late afternoon before
decreasing. Shifting gears here, while mostly quiet conditions are
expected through tonight; can`t completely rule out a few spotty
showers with isolated thunderstorms developing this afternoon and
evening as another weak shortwave "rides the ridge" into our area.
Given the 1000-2000 J/kg of instability and limited shear (<30kts)
across the area, severe weather is not expected. However, can`t
completely rule out an occasional bolt of lightning and a quick
0.10" of an inch of accumulation with the strongest updrafts. Since
this activity will be mostly diurnally driven, should see this
activity gradually weaken as we lose daylight. Lastly, with mid-
level ridging overhead; a combination of lighter surface winds and
higher dew points will likely lead to areas of locally dense fog
redeveloping overnight mainly along and east of I-29. With
visibilities of a mile or less possible through mid-morning, make
sure to give yourself some extra time when making those morning
commutes.

WEDNESDAY & THURSDAY: Looking into midweek, the previously mentioned
ridging will continue to sit over the plains aloft keeping most of
the precipitation chances at bay. With light and variable surface
winds becoming more southeasterly winds by Wednesday afternoon,
shouldn`t see much changes in the temperature profiles with highs
expected to be mainly in the 80s to low 90s through Thursday.
However, as a cold front arrives late Thursday; we`ll likely see our
shower and thunderstorm chances (40%-60%) increase but there is
still some lingering uncertainty. Looking at 19.12z guidance, most
models vary slightly in the times of arrival of the front and
subsequent mid-level wave. There is also some uncertainty in areal
extent/coverage as some guidance has convection developing along the
whole front or just the northern portions of the front. With the
better lift/energy expected to progress north of us with the mid-
level wave, my gut is saying that things will initially develop
north of us across northeast SD and central MN then gradually spread
southwestwards along the front into areas north of I-90. With this
in mind and an unstable airmass characterized by 2000-3000 J/kg
and 30-40 kts of shear; there`s definitely an isolated to
scattered risk for stronger storms along the front; but the main
questions are where and when. Until we can iron out the finer
details, we`ll have to continue to monitor the late Thursday to
early Friday timeframe for clarity.

FRIDAY ONWARDS: Heading into the extended period, northwesterly flow
returns as the Hudson Bay trough strengthens and rotates across the
Northern Plains/Great Lakes regions. With multiple pushes of cold
air advection (CAA) aloft as waves rotate through expect the first
tastes of fall heading into the new week as temperatures gradually
decreasing into the upper 60s to mid 70s across the area. Otherwise,
mostly quiet conditions are expected heading into midweek.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1033 PM CDT Tue Aug 19 2025

Winds will be light and variable, allowing for patchy dense fog
formation, especially for areas along and east of the James River
Valley. Visibility may be reduced to less than 1 mile at times.
Confidence in fog formation is medium to high. KHON and KSUX are the
sites most likely to see IFR to LIFR visibilities. Fog is expected
to burn off quickly as we begin to mix in the morning. Quiet
conditions for the remaining part of this cycle.

&&

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

&&

$$

DISCUSSION...05
AVIATION...AJP