893
FXUS63 KFSD 241948
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
248 PM CDT Tue Jun 24 2025

.KEY MESSAGES...

- Highly favorable pattern for repeated rounds of thunderstorms
  with heavy rain ahead. Initial focus begins into Wednesday
  morning, with highest potential for significant rainfall
  Wednesday evening into the overnight.

- 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.

- Greatest heavy rain risks will bring increased risks for
  urban and small stream flash flooding. Area river forecast
  continue to suggest some flooding potential, but recent
  drought may suppress higher level potential.

- Isolated severe storm risks will be possible through the next
  two days, focused mostly with elevated hail and very brief
  wind gusts along a boundary.

- The end of the week break in rain will be short-lived with
  thunderstorm risks returning this weekend. Some severe weather
  potential is possible.

&&

.DISCUSSION...
Issued at 244 PM CDT Tue Jun 24 2025

THIS AFTERNOON: Throughout the day we`ve been impacted by
several subtle shortwaves moving through the broad southwesterly
flow. These waves, combined with weak low-lvl warm advection
have allowed showers and thunderstorms to persist. With PWAT
values approaching 150% of normal, we`ve already observed
rainfall totals over 1-2" in highly localized pockets. Water
vapor and latest analysis suggest latest band of mid-lvl
vorticity will slide east of the Mid-Missouri River valley early
this evening, so will maintain higher end Pops along or south
of I-90 into early evening.

TONIGHT:  As we move through the evening, we`ll begin to watch two
areas of focus, one over western Nebraska and Kansas and a second
area along a stalled frontal boundary stretching across central Iowa
into southern Nebraska.  The combination of increasing mid-lvl
vorticity and associated influence of the LLJ will develop
widespread convection in both areas later this evening.
Convection will lift northeastward toward the MO river valley
and Tri-State area midnight, overtaking most of the CWA near or
after daybreak. PWAT values are likely to surpass the 2 to 2.25"
mark (AOA 190% of normal) by Wednesday morning. While the
progressive nature of the mid-lvl vorticity will lead to more
progressive radar echos, as we`ve seen this afternoon, ANY
rainfall will produce moderate to heavy rates. So while there is
a bit of uncertainty on the overall focus of the heaviest
rainfall, HREF LPMM guidance into mid-morning Wednesday would
suggest localized totals of 2 to 3" may be possible especially
over southwest Minnesota, within a larger area of 0.50" 1.5".

WEDNESDAY:  This lead wave will move into western Minnesota by mid
to late morning, but as often happens in these setups a trailing
corridor of stronger 850mb winds (and associated convergence) may
continue into the afternoon.  With modest elevated instability (AOA
1500 J/KG) some scattered elevated stronger storms may be possible
through the day mostly along and south of I-90.  The biggest
question mark for Wednesday will be just how far north the 925:850
mph front and associated surface front will be pulled north
overnight.  Two scenarios may develop by late in the day.  Should
the ECMWF/CMC/GFS verify the fronts are pulled far enough north to
greatly increase the heavy rain risks over areas from Yankton
to Sioux Falls and Windom and areas southeast. Should the
NAM/FV3/ARW verify, overnight convection will do a better job
suppressing the front further southeast, really focusing the
heaviest rain risks into Wednesday evening/night along areas
from Sioux City to Spencer.

All that said, we should begin to see a marked increase in
convection along the low-lvl instability gradient early
Wednesday evening as another round of mid-lvl vorticity moves
into the Plains. Low-lvl convergence into the east to west
elevated boundary should maintain a persistent convective risk
deep into the night. There is certainly an increased risks for
locally heavy rain throughout the Tri-State area into Thursday.
HREF LPMM guidance suggest some higher end totals (in addition
to anything that falls into Wednesday morning), could be in the
3 to 5" range. For the official forecast, leaning much closer to
the 90th percentile NBM QPF forecasts through this event,
especially along areas where the frontal boundary may reside
near NW Iowa.

This amount of rain may cause some issues throughout the region,
both from a perspective of the potential rate of rainfall but also
quantity.  Storm motion tonight into Wednesday may owe to more brief
urban and small stream issues.  A secondary round of rain late
Wednesday into Thursday will begin to pull in the aforementioned
risks, but also some potential for river responses. Recent
drought conditions however have left us at a much lower starting
point on river than conditions one year ago that led into
widespread flooding. While a flood watch will not be issued
today, depending on how convection tracks tonight into
Wednesday, watches may be possible for portions of the area.

THURSDAY-FRIDAY:  High pressure moves into the area for Thursday and
Friday, bringing a return of drier conditions but also cooler
temperatures on Thursday.  The return of westerly mid-lvl flow
pushes the thermal ridge east on Friday bringing warmer
temperatures.

SATURDAY-SUNDAY: Quasi-zonal flow returns for the upcoming weekend,
with several shortwave troughs moving through the Northern Plains. A
great deal of uncertainty builds through the weekend regarding
return flow ahead of these waves. There may certainly be some
stronger convective risks along a weak frontal boundary through
the central Dakotas Saturday and then over the eastern Dakotas
and Minnesota Sunday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1213 PM CDT Tue Jun 24 2025

Scattered showers and isolated thunderstorms may continue in
areas along and south of I-90 through the afternoon. CIGS
remain at VFR levels, but some MVFR ceilings are possible
towards the Missouri River and Sioux City areas later
this afternoon.

Greater uncertainty builds this evening, with models struggling
on the potential for additional isolated to scattered showers.
Greater rain chances arrive after midnight, or moreso after 4am
and continue through mid-morning. CIGS may fall below MVFR
levels at times, with visibility restrictions as low as 1-2
miles in heavier rain.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Dux