Lennox, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

305
FXUS63 KFSD 121940
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
240 PM CDT Tue Aug 12 2025

.KEY MESSAGES...

- There is a Level 2 of 5 risk for severe thunderstorms
  Wednesday night for areas west of Highway 281 and a Level 1
  of 5 risk extending to the east from near Marshall to Sioux
  Falls to Vermillion. The strongest storms will be capable of
  producing wind gusts to 70 mph, half-dollar size hail, and
  locally heavy rain.

- High heat and humidity return Thursday through the weekend.
  Afternoon heat index values could approach 100 degrees,
  especially south of I-90 on Friday and Saturday.

- An active weather pattern brings low to moderate chances
  (20-40 percent) for showers and thunderstorms Thursday night
  through the weekend. Severe weather cannot be ruled out, but
  confidence in any details is low.

&&

.DISCUSSION...
Issued at 240 PM CDT Tue Aug 12 2025

Surface high pressure firmly in place across the region will
keep skies mostly sunny/clear through tonight. Winds will be
light and temperatures will drop into the mid 50s to lower 60s.
Will need to watch for the development of some patchy dense fog
across northwest Iowa, especially within river valleys, but it
should quickly burn off by mid-Wednesday morning.

High pressure drifts eastward Wednesday, allowing return
southerly flow to develop. As a result, expect increasing
temperatures and humidity. While there could be some lingering
morning light rain showers/storms from overnight West River
convective activity mainly west of I-29, main focus will be
Wednesday night when guidance shows a short-wave trough moving
through the broader synoptic 500 hPa ridge. 12Z model suite has
slowed this feature down, so current thinking is that the
majority of convective activity should remain west of the
forecast area through at least 7 pm and perhaps as late as 10
pm. By this time, model soundings show a modest near-surface
thermal CAP, which should keep storms elevated. In addition,
instability aloft decreases from west (around 2500 J/kg) to east
(around 1000 J/kg of less), so storms are expected to weaken
with eastward extent. The strongest storms will be capable of
producing wind gusts to 70 mph, half dollar size hail, and
locally heavy rain. This is covered well in SPCs latest Day 2
Outlook, which did introduce a Level 2 of 5 (slight) risk for
areas west of Highway 281.

Thursday into the weekend, 500 hPa ridge reasserts itself across
the southern/central Plains, resulting in increasing temperatures.
Highs in the upper 80s to mid 90s by Friday/Saturday and
dewpoints back into the 70s may result in heat index values
approaching or exceeding the 100 degree mark, especially south
of I-90. In addition, there will be periodic thunderstorm
chances (20-40 percent) as quasi-zonal flow aloft and associated
short-waves are squeezed between the ridge to the south and a
deep trough across the southern Canadian Prairies. While not
outlooked yet by SPC, some storms may become strong to severe
each day Thursday through Saturday as a southward sagging
frontal boundary looks to stall out somewhere across the region.
This idea is supported by the latest machine learning severe
probabilities. All that said, overall confidence in mesoscale
details and timing are low at this time, so will likely need to
take it a day at a time.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1242 PM CDT Tue Aug 12 2025

With patchy fog and smoke from earlier this morning finally to
the east of TAF airfields, expect VFR conditions through the
period. Outside of some afternoon thermal cumulus around 5000 ft
agl, skies should be mostly sunny/clear. The one potential
caveat is at KSUX, where some guidance suggests the redevelopment
of fog Wednesday morning along the Missouri River (20-50 percent
chance). Confidence not high enough at this time to include in
the 18Z TAFs, but something to monitor with future forecasts/
updates.

Winds will be light from the northwest this afternoon with some
gusts up to 20 kts at KHON/KFSD. Winds will then become light
and variable tonight, before turning to the southeast toward the
end of the forecast period.

&&

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

&&

$$

DISCUSSION...Rogers
AVIATION...Rogers