100
FXUS63 KFSD 220338
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1038 PM CDT Mon Jul 21 2025

.KEY MESSAGES...

- An active pattern continues for much of the upcoming week,
  with nearly daily thunderstorm risks. However, confidence is
  low on coverage and location of storms.

- Temperatures and humidity also rise this week. A Heat
  Advisory is in effect for locations along the Missouri River
  and west of the James River today from noon to 8 pm for heat
  indices exceeding 100F. Additional heat headlines may be
  needed on Tuesday.

&&

.DISCUSSION...
Issued at 245 PM CDT Mon Jul 21 2025

TODAY: Looking aloft we see a broad, shallow ridge centered over the
central United States. At the surface, winds are southerly and
breezy at 10-15 mph with gusts up to 20 mph. With the southerly
winds comes a strong push of WAA and an influx of higher dew points.
Highs today were limited somewhat by thick stratus. Bumped highs
down just a little with a blend of NBM/NBM 25th percentile. Highs
now look to peak in the low 80s to 90s with the highest temperatures
west of the James River Valley. Dew points are expected to reach the
mid to upper 70s. The previous forecast anticipated heat index
values reaching the 100-105 deg F range. Current conditions are
falling short of those values. However, if the clouds continue to
burn off expect that rapid warming will take place. As such, have
decided to leave the current Heat Advisory in place.

This afternoon a "ridge rider" shortwave will work through the upper
pattern and may work as a trigger for isolated strong to severe
thunderstorms. Storms are most likely to form in northwestern Iowa
this afternoon and into the evening. Through the day the atmosphere
will destabilize as the aforementioned dew points increase.
Mid- level lapse rates increase to around 8 deg/C, CAPE to
2000-4000 J/kg, but 0-6 km Bulk shear remains marginal at around
30 kts. Despite the more favorable atmosphere, the mid-levels
will remain strongly capped with a 10k+ foot deep warm layer.
So, the big question is: will convection initialize at all? If
it does, storms will most likely be elevated and present a large
hail (1-1.5 inches) and damaging wind threat (60-70 mph). This
assessment matches well with the current SPC Day 1 outlook for a
Marginal (level 1 of 5) risk. While initially discrete, these
storms would likely grow upscale into a line as the deep layer
shear is parallel to the front.

TUESDAY: Showers and thunderstorms could linger into Tuesday
morning, however guidance is in very low agreement on that. Tuesday
will be very similar to Monday with hot and humid conditions.
Convection over eastern Nebraska and morning clouds may have an
impact on our highs once again. As it currently sits, highs will
climb into the upper 80s to 90s with a few 100s possible over
central South Dakota. After discussion with the neighboring offices,
have decided to hold off on issuing heat headlines for Tuesday due
to the uncertainty of the morning convection. Breezy southerly winds
keep strong WAA going and once again pushes dew point temperatures
into the mid to upper 70s. A similarly unstable environment to today
will be present, with a strong, mid-level cap. Another ridge rider
short wave works through the pattern, possibly triggering isolated
to scattered strong to severe thunderstorms. Like Monday, these will
most likely be elevated if they can initiate at all. Coverage and
location of initiation remain highly uncertain and will likely
depend on how storms progress from the previous night/early Tuesday
morning.

WEDNESDAY: Wednesday morning the stalled front begins to drift north
with the surface low pressure as it moves northeast out of northern
Colorado/southern Wyoming. Continued strong WAA and moisture
advection will result in one more hot and humid day. Highs will
climb to the mid 80s to 90s, with dew points in the low to mid 70s.
Through the day the surface low pressure will continue to drift
northeast through the region, dragging a cold front with it. This
cold front will act as a foci for more widespread strong to severe
thunderstorms Wednesday afternoon and evening. At this time
many details are uncertain, but general agreement in mid-range
guidance indicates a moderately favorable environment for all
modes of convection. Current timing looks to be Wednesday
afternoon through the overnight hours. Details of this forecast
will change with additional information, so be sure to check
back for updates. Especially if you have overnight outdoor
plans.

REST OF THE WEEK: Flow aloft become slightly more zonal, with
continued shortwaves flowing through. This keeps shower chances in
the forecast for the majority of the remaining week. Highs will be
slightly cooler behind the front on Thursday, in the low to mid 80s.
Friday temperatures warm into the upper 80s, and will be in the
upper 80s to 90s for the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1030 PM CDT Mon Jul 21 2025

Mostly VFR conditions will transition to mostly MVFR to IFR
conditions this TAF period mainly due to developing stratus.
Taking a look at satellite imagery, higher dew points have led
to the development of areas of MVFR to IFR stratus east of I-29
this evening. From here, expect the stratus to gradually expand
westwards towards the I-29 corridor overnight acting like areas
of fog at times. With this in mind, could some occasional LIFR
ceilings and vsby especially across southwestern MN through the
mid-morning hours on Tuesday. Otherwise, predominantly southerly
surface winds will continue into Tuesday with periodic breeziness
in the afternoon hours to end the TAF period.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...05