496
FXUS63 KFSD 292313
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
613 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- An unsettled wet pattern will prevail through most of the
  holiday weekend. Severe weather risks are low, but non-zero
  risks for a few weak funnel clouds with developing afternoon
  showers today (south-central SD) and Saturday (northern
  through eastern portions of the area).

- Isolated to scattered stronger showers are possible tonight
  into Sunday. A Marginal risk (level 1 of 5) of storms becoming
  severe exists over south central South Dakota. Threats with
  strong storms include hail to the size of a quarter and wind
  gusts to 60 mph.

- Areas of heavier rainfall are possible tonight into Sunday.
  Low to moderate (20-40%) chance of exceeding 1 inch focused
  south of I-90 and especially toward the Missouri River Valley.

- Another round of showers and thunderstorms are possible
  Tuesday. Some of these could be strong to severe.

- Brief shot of colder air pushes into parts of the northern
  Plains/Upper Midwest mid-late next week.

&&

.DISCUSSION...
Issued at 230 PM CDT Fri Aug 29 2025

THIS AFTERNOON AND TONIGHT: Showers and weak thunderstorms
continue to form along a surface trough axis as an upper wave
and surface low push slowly eastward. As mentioned in the
previous discussion, rain should stay generally west of Highway
81 due to dry low and mid levels in areas to the east. Central
South Dakota will see increasing moisture in the low and
midlevels thanks to moisture advection ahead of the oncoming
system. Shear and instability are low, and so severe weather is
not expected. However, a few stronger updrafts are possible
along a surface boundary that may result in isolated
thunderstorms with wind gusts around 45 mph. In addition, a
region of enhanced environmental vorticity aligns well with
enhanced stretching potential over central South Dakota that may
result in brief, weak funnels this afternoon. Highs for this
afternoon will climb to the upper 70s to low 80s. Lows tonight
will fall to upper 50s to low 60s.

Tonight the upper wave and surface low enter south central South
Dakota to north central Nebraska. The wave will deepen slightly as
it does so, resulting in an increase in shower activity. Light,
scattered showers will push into eastern South Dakota and Nebraska,
and western Minnesota and Iowa. Showers in the warm sector of the
low (south central SD and north central NE) will increase in
intensity. Severe weather is low risk, but with the increased
forcing an isolated strong to severe thunderstorm is possible. If
they do form, risks include hail to the size of a quarter, and wind
gusts to 60 mph. SPC Day 1 outlook includes the area at highest risk
in a Marginal (level 1 of 5) risk for severe thunderstorms. Gregory
county is currently our only county included in the Marginal.

The RAP and HRRR both indicate tall, skinny CAPE profiles which
indicate the potential for heavy downpours. This is corroborated
with the NAM nest, HRRR, and RRFS rain rates of around 0.5-1.5
in/hour. Mean flow of only 5-10 kts means storm motion will be slow.
All of this combined leads to increased risk of localized ponding
and rises on small creaks and streams, as well as urban flooding.
This analysis aligns well with the WPC slight risk (level 2 of 4)
for excessive rainfall over central South Dakota. Risk of
widespread flooding is low, however, due to a general lack of
rain in that area this summer. The heavier rain rates will
decrease as we approach daybreak Saturday.

SATURDAY-MONDAY: Highs for the next three days will be cooler, in
the 70s. Through the day Saturday the upper wave will slowly close
off and the whole system will continue to slowly drift east. A
band of increased vorticity as the upper wave tightens may result in
increased shower activity across south central and southeastern
South Dakota, north central and northeastern Nebraska in the
afternoon. Additionally, the increased vorticity will be located
along the warm front and an area of enhanced stretching potential.
This could result afternoon weak funnels situated from roughly Huron
southeast to Jackson MN.

As we head into Saturday evening rain showers expand northward, and
isolated to scattered showers push into areas east of I-29. Sunday
the system stalls for a few hours and spins directly over
southeastern South Dakota. Showers expand in areal coverage
over the whole region by Sunday afternoon. Monday morning
the system begins to accelerate and move southeast out of the
region. By about midnight Tuesday morning most showers will have
ceased.

Rain totals will be highly dependent on the track of the system. In
general, we are expecting widespread totals of a quarter to an inch
of rain. Currently the GFS and CAN keep a more northerly track,
meaning higher totals in south central South Dakota. The EC and NAM
take a more southerly track, meaning higher totals over north
central Nebraska. Whichever solution pans out, the area of
highest rain is expected to range from 1-3 inches with isolated
pockets of higher possible. Again, we are not expecting
widespread flooding due to the general lack of rain over central
South Dakota. However, further shifts in track could have an
impact on small streams and creeks. Should you come across any
roads with flowing water over them, do not drive through. Turn
around, don`t drown!

TUESDAY-MID WEEK: The break in rain will likely be brief, as a
strong upper trough digs south from Canada into North Dakota and
South Dakota. Long term guidance is in low agreement on how this
next system plays out. But in general this stronger system may bring
chances for strong to severe thunderstorms. Stay tuned for more
details as they become available. The rest of the week looks to be
dry, but cool. Highs Tuesday will be in the 70s, but Wednesday and
Thursday look to warm only to the 60s. Friday warms back into the
70s.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 610 PM CDT Fri Aug 29 2025

Scattered showers and isolated thunderstorms will remain
primarily focused from the James River and westward through at
least Saturday morning - as low pressure through south central
SD and NE remains nearly stationary through the period. There
will be some expansion to the east on Saturday afternoon, but
confidence is low on precipitation chances at the TAF sites due
to the scattered nature of the showers and storms, as well as
being located along/to the east of the better rain chances.
Winds will remain light southeasterly through the period.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...JM