Le Mars, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

425
FXUS63 KFSD 262247
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
547 PM CDT Sat Jul 26 2025

.KEY MESSAGES...

- A Heat Advisory remains in effect for areas along and west of
  the James River Valley through 8 pm CDT, where heat index
  values of 100 to 104 degrees are expected.

- Dangerous heat intensifies Sunday/Monday given a combination
  of air temperatures in the 90s to near 100 degrees and dew
  points predominantly in the 70s. Heat index values are
  forecast to rise above 104 degrees for most areas. The Extreme
  Heat Watch has been upgraded to an Extreme Heat Warning.

- There is a 20 to 40 percent chance for showers and
  thunderstorms Sunday night into Monday. Storms could be strong
  to severe with the primary hazard being wind gusts to 70 mph.
  Additional strong to severe thunderstorms are possible Monday
  night into Tuesday.

- Temperatures cool significantly by the middle of next week,
  peaking in the 70s Wednesday onward.

&&

.DISCUSSION...
Issued at 246 PM CDT Sat Jul 26 2025

Low stratus/fog from this morning has finally mixed out along and
west of I-29. Farther east, a scattered cumulus field remains
across southwest MN and northwest IA, but is also expected to
dissipate through the afternoon. Despite delayed maximum solar
for some areas west of the James River due to this cloud cover,
temperature/dewpoint trends are largely on track. As a result,
still expecting heat index readings in these areas to reach or
slightly exceed 100 degrees by late afternoon/early evening.
Current Heat Advisory is in good shape with no changes planned.

19Z water vapor loop shows a short-wave across WY/CO and this will
be the focus for evening showers/thunderstorms as it lifts east-
northeast. 12Z model suite in good agreement, showing the best upper
level support across central/northeast SD and this is supported by
the CAMs, keeping the forecast area mainly dry through the evening.
A few stray showers/isolated storms may make it east of the MO
River, but should quickly dissipate.

HREF less aggressive with probabilities for stratus/fog tonight
with the highest chances of 30 to 50 percent for 1-3 mile
visibility restrictions mainly east of Hwy 59 across northwest
IA. Will continue to carry patchy fog in these areas, but
monitor trends for possible westward expansion.

Sunday, strong 500 hPa ridge axis moves overhead with 925 hPa
temperatures from +28 C across the east up to +35 C across the west
by 00Z Monday. Highest air temperatures near 100 degrees west of the
James River will be offset by the highest dewpoints in the mid to
upper 70s across MN/IA, but the combination of the two will result
in maximum heat index values from 105 to 110 degrees across
most of the forecast area. Not all areas will top the 105 degree
mark, especially the higher terrain along the Coteau/Buffalo
Ridge, but given weekend outdoor activities and the potential
for temperatures/dewpoints to overperform the current forecast,
will upgrade the entire Extreme Heat Watch to an Extreme Heat
Warning from Noon to 8 pm. Regardless of the exact heat index,
dangerous conditions will be in place region-wide. Practice
heat safety by limiting time outdoors, remaining well hydrated,
and taking frequent breaks in air-conditioned spaces if being
outside is a necessity.

Sunday afternoon/evening, the next in a series of short-waves
moves along the International border, likely firing convection
across ND/northern MN. Guidance suggests this activity may
interact with any residual outflows from tonight`s storms and
potentially build southwestward along a weak inverted trough/
surface boundary into the forecast late Sunday evening.
Predictability is low, especially given the strength of the CAP
farther south, but the strongest storms may become severe with
the primary hazard being damaging wind gusts to 70 mph. Large
hail to quarters and localized heavy rainfall are also possible.
SPC`s Day 2 Outlook, showing a Level 1 of 5 (marginal) risk
covers this potential well.

Given the large-scale pattern, Monday has the potential to be as
hot as Sunday, but given uncertainties concerning convection
and cloud cover, will hold off on any heat headlines at this
time. If thunderstorms remain to the north/northeast of the
forecast area, afternoon heat index values are likely to top 100
degrees and up to 110 degrees along the MO River Valley and
into parts of northwest Iowa.

Monday night into Tuesday stand the best chance of seeing more
widespread shower and thunderstorm activity across the forecast
area as another short-wave moves through quasi-zonal flow aloft
atop the expansive central/southern CONUS ridge. Given extreme
instability ahead of the wave and ample deep layer shear, severe
thunderstorms are once again possible. But with each new round
of storms being dependent on the timing, location, and evolution
of any previous activity, predictability is still low. For now,
SPC`s Day 3 Outlook keeps the region in a Level 1 of 5 (marginal)
risk for severe storms.

A strong cold front drops south across the region Tuesday night
in association with a large Hudson Bay low, bringing yet
another chance for showers and thunderstorms. As has been
advertised, temperatures Wednesday through the rest of the week
will be significantly cooler, topping out in the 70s each day.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 545 PM CDT Sat Jul 26 2025

Isolated to scattered thunderstorms are developing over central
SD this evening, though hi-res guidance indicates this activity
remaining to the west of KHON tonight. Otherwise, fog looks
less likely tonight, with latest ensembles showing a less than
10% probability for fog formation at the TAF sites overnight -
with higher probabilities residing farther east through central
IA. Southeasterly winds will remain on the lighter side tonight,
then increase on Sunday morning and gust to around 20 kts
through the afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Extreme Heat Warning from noon to 8 PM CDT Sunday for
     SDZ038>040-050-052>071.
     Heat Advisory until 8 PM CDT this evening for SDZ038-039-050-
     052>054-057>061-063>066-068>070.
MN...Extreme Heat Warning from noon to 8 PM CDT Sunday for MNZ071-
     072-080-081-089-090-097-098.
IA...Extreme Heat Warning from noon to 8 PM CDT Sunday for
     IAZ001>003-012>014-020>022-031-032.
NE...Extreme Heat Warning from noon to 8 PM CDT Sunday for NEZ013-
     014.

&&

$$

DISCUSSION...Rogers
AVIATION...JM