Le Mars, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

417
FXUS63 KFSD 272352
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
652 PM CDT Fri Jun 27 2025

.KEY MESSAGES...

- Strong to severe storms are possible this evening west of
  I-29, with initial development across south central South
  Dakota. Large hail to 2 inches and wind gusts to 70+ mph are
  the main threats. An isolated tornado cannot be ruled out.

- Additional strong to severe storms are possible Saturday and
  Sunday during the afternoon/evening hours. Though each day`s
  storm threat will be determined by the previous day`s storms.
  Continue to monitor the forecast if you have outdoor or
  travel plans.

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

&&

.DISCUSSION...
Issued at 251 PM CDT Fri Jun 27 2025

Quiet conditions persist through the first half of the afternoon
hours today. However, things will change over the next few hours as
thunderstorms develop along a boundary across south central South
Dakota. These storms may be capable of large hail up to about 2
inches in diameter as the storm mode will be discrete during initial
development. Storms look to quickly grow upscale into a mesoscale
convective system (MCS) as they push eastwards which will transition
the threat from large hail to damaging winds. Given steep low level
lapse rates, and very high DCAPE values exceeding 1,500 J/kg,
damaging winds to 70+ mph will then be the main threat. This
damaging wind threat looks to be the main hazard for the forecast
area though the large hail threat will coincide with it if a
discrete storm can develop ahead of the line. At the same time,
there could be an isolated tornado as well with 0-3 km shear vectors
with magnitudes of about 25 knots oriented perpendicularly off the
MCS. Once the storms push into and east of the Missouri River
Valley, they should weaken with eastward extent as capping will
strengthen via nocturnal stabilization. The low level jet will also
be strengthening during this period of time as well. That said, this
cap will not be moist and lifting will above the cap results in
little to no instability. Thus, think that if any showers or storms
persist through tonight, they will not be severe. Overnight low
temperatures will fall to the 60s.

Severe weather chances continue through Saturday though there
remains uncertainty in this potential. The general consensus for
severe storms amongst the 12z guidance is for storms to develop
along the warm front but the location of this front is driving the
uncertainty. The front looks to end up just northeast of the area.
However, this can still change depending on how tonight`s storms
shake out. With mean flow paralleling the boundary, storms look to
quickly grow upscale into a line. At the same time, a stout elevated
mixed layer (EML) will be in place with mid level lapse rates
approaching 9C/km. This will present large capping across the
forecast area and could inhibit convection to a large degree. The
main question will be if diurnal heating will be strong enough to
mix out the cap. While high temperatures will reach into the upper
80s and 90s across the area, questions still remain if highs will
warm a bit more to potentially the mid to upper 90s or even low
100s. However, both the REFS and HREF show a near 0% chance for
highs to exceed 100F. IF storms are able to develop, they would
likely be in a line spanning back from the previously mentioned
boundary down the dry line. Large hail will be possible with initial
updrafts but quick upscale growth will quickly transition the main
hazard from large hail to damaging winds. To account for this
potential, did keep broad chance PoPs across the area.

The other aspect to Saturday is that it is going to be hot and
humid. With highs warming to the upper 80s and 90s while dew points
moisten to the 60s and 70s, heat indices will be up into the 90s to
nearing 100F. Did think about issuing heat headlines but given how
borderline the environment is, decided to hold off on issuing
headlines at this time. Will continue to monitor this potential. Low
temperatures will fall to the mid to upper 60s overnight.

Severe threat looks to continue into Sunday though this looks be a
more isolated threat. This potential will be contingent on how fast
the boundary is able to push out of the area. Per the GFS, Canadian,
and Euro ensembles, the front looks to be pushing just southeast of
the area during the early to mid afternoon hours. This looks to keep
convection just out of the area. This is supported by the NBM as it
shows the highest probabilities for exceeding a tenth of an inch of
rain off to the southeast. Will still monitor the potential for
convection to develop earlier than currently anticipated though.
Outside of rain and storm chances, Sunday will be a cooler day with
highs only warming to the 80s with northerly winds keeping a light
breeze in place. Lows will fall to the 60s overnight.

Next week looks to begin on the dry side as the shortwave
responsible for the end of week and weekends storms will push east
of the region. This will keep high temperatures near to just above
normal for this time of year in the 80s to low 90s.

Upper level ridging over the southern CONUS could result in ridge
riding shortwaves that may bring storm chances back to the Northern
Plains. However, too far out to say for sure about any details just
yet. Will continue to monitor this potential. Aside from rain
chances, highs will remain in the

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 652 PM CDT Fri Jun 27 2025

Low confidence thunderstorm forecast throughout this TAF period,
and thus have just a short window of TS for KFSD focused 05Z-07Z
if storms developing in central SD/NE can remain organized as they
move east late evening-overnight. Additional low thunderstorm
chances return toward the end of this period, but again confidence
is low when/where, or even if storms develop prior to 29/00Z.

Aside from isolated-scattered storms, a strengthening low level
jet will produce a period of non-convective low-level wind shear
(LLWS) late evening through shortly after sunrise. South winds
gusting 20-25kt are also expected to develop Saturday afternoon.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...JH