522
FXUS63 KFSD 251124
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
624 AM CDT Wed Jun 25 2025

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms capable of
  producing heavy rainfall will occur during the next 36-48
  hours. Highest potential for heavy rainfall will occur tonight
  into Thursday morning.

- Widespread amounts of 1 to 3" are possible, with several
  indicators of heavy rain of 3 to 5" focused through NE
  Nebraska, NW Iowa, and adjacent areas of MN/SD.

- There is some risk for small streams and creaks to rise over
  their banks, as well as localized urban street flooding. Area
  river forecast continue to suggest some flooding potential,
  but recent drought may suppress higher level potential.

- Wednesday night, there is potential for strong to severe
  thunderstorms to form along the boundary. Risks include heavy
  downpours, wind gusts to 60 mph, and large hail to an inch in
  diameter. Though unlikely, a tornado is possible.

- A brief break in the rain Friday and Saturday before
  thunderstorm chances return Sunday.

&&

.DISCUSSION...
Issued at 354 AM CDT Wed Jun 25 2025

TODAY: Today, despite the rain, highs will warm into the 70s and 80s
thanks to persistent WAA. The forecast remains largely on track
for 36-48 hours of widespread, periodically heavy rain fall. A
mid-level wave has moved north out of western Nebraska into
central South Dakota and will continue to move northeastward
through the day today. With it comes a strong push of WAA and a
vorticity max that is triggering showers and thunderstorms.
These storms will progress northeastward with the wave,
expanding in coverage to include the majority of the County
Warning Area by daybreak. As the day continues, elevated
instability of 1000-1500 J/kg CAPE and marginal 0-6 km Bulk
Shear of less than 30 kts could spawn an occasional stronger
thunderstorm. But the greater risk for strong to severe
thunderstorms will come this evening.

Through the day today, WAA will continue to pull warm, moisture rich
air northward into the region increasing instability, and pooling
against the west-to-east orientated front. The 0-6 Bulk shear
increases as the LLJ picks up and the main upper wave begins to lift
northeastward from central South Dakota into southwestern Minnesota.
The area of greatest convergence, just to the south of boundary,
will serve as the focus for strong to severe thunderstorm initiation
Wednesday evening and into the overnight. Low level lapse rates are
steep, but there is a deep warm layer (10-12 thousand feet). This
leads me to believe the primary threat will be damaging wind gusts
to 60 mph, and quarter sized hail. Though unlikely, a tornado cannot
be ruled out. These are in addition to the heavy rainfall that any
storm will be capable of producing.

There remains some question on how far north the 925-850 mb front
will be pushed. This will greatly impact where the highest rain
totals, and where the greatest severe threat will be. Some of the
models in the 00Z run have flip-flopped from the previous forecast.
There still remains two scenarios. In the first scenario, the ECMWF
and the NAM nest indicate the front will move further north.
(Previously the NAM had a more southerly track) If this is the case
the heavier rainfall will be southeast of a rough line from Wagner-
Salem-Tracy. The second scenario is shown by the GFS and Canadian
that indicate the front will remain farther south. (Previously the
GFS had a more northerly track) Should this scenario play out, the
heaviest rain will fall southeast of a rough line from Yankton-
Luverne-Jackson. Overall, ensemble guidance indicates a slight trend
north in the heaviest precipitation. If this trend holds, the most
likely scenario would be scenario one.

When it`s all said and done, widespread totals of 1-3 inches are
expected across the region. As mentioned previously, higher amounts
are possible but will be highly dependent on where the front
settles. Areas of northeastern Nebraska, extreme southeastern South
Dakota, northwestern Iowa, and southwestern Minnesota could see
totals closer to 3-5 inches, with pockets of higher possible. This
raises the question of flooding. This morning`s storms are more
likely to result in some localized ponding and urban street
flooding. As we continue into tonight with the potentially stronger
thunderstorms, we may begin to see small creeks and streams overrun
their banks. Some localized flash flooding is possible. Thanks to
the recent dry weather, our rivers are at or below normal for this
time of year. While there will likely be river rises, most should
remain below flood stage. A few may come close to minor flood stage,
but it`s too early to tell what rivers may reach that point. With
the uncertainty in the location of the heaviest rainfall, have opted
not to issue a Flood Watch tonight after collaboration with
neighbors.


THURSDAY-NEXT WEEK: Thursday showers will linger through the early
afternoon before tapering off in the evening. Highs will reach the
70s to 80s with the warmest temperatures along the Missouri River
Valley. Friday, flow aloft becomes west-southwesterly, drying things
out. A strong push of WAA will help warm highs into the 80s and 90s.
By Saturday the flow aloft becomes more westerly, keeping us dry and
warm during the day. Highs are expected to climb into the 90s. A
short wave will move north of the region Saturday night, bringing
another round of showers and thunderstorms for Saturday night into
Sunday. For the first half of next week, a ridge of high pressure
will move into the region. Sunday through Wednesday temperatures
will be seasonably warm, in the 80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 623 AM CDT Wed Jun 25 2025

Scattered showers and thunderstorms will increase in coverage
through this morning. A mix of VFR to IFR conditions are expected to
continue through the end of the period, and will depend on the
prescience of stronger storms. A brief afternoon lull will be
followed by reintensification this evening and into the overnight.
This second round could produce isolated strong to severe
thunderstorms, with the greatest risks being wind gusts of 50 kts,
hail to the size of quarters, and possibly a tornado. The area most
likely to experience stronger storms is southeast of a line from
KYKN to KFSD to KDVP, but there is uncertainty in where the boundary
will set up, and thus where the strongest storms will be.
Additionally, storms will produce heavy rainfall at times which
could result in reductions in visibility to less than 4 miles.

Winds during this time will be southeasterly around 10 kts with
occasional afternoon gusts to 18 kts. Along and south of I-90,
surface winds will become southerly in the afternoon. Winds will
become light and variable after sunset.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...AJP