592
FXUS63 KFSD 080346
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1046 PM CDT Sun Jun 7 2026

.KEY MESSAGES...

- Isolated severe storms are possible mainly west of I-29 on
  Monday. Large hail up to golf ball size and damaging winds to
  65 mph will be the main hazards should a storm develop.
  Another chance for storms is possible Monday night though this
  potential is more uncertain.

- There is a moderate chance (40-90%) of highs exceeding 90F
  Tuesday and Wednesday, with the highest probabilities coming
  on Tuesday. Be prepared to enact any heat related safety
  measures.

- Severe storm chances look to make a return to the region on
  Tuesday and Wednesday. Details remain uncertain so continue to
  keep up to date with the latest forecast for the most up to
  date information.

&&

.UPDATE...
Issued at 920 PM CDT Sun Jun 7 2026

Taking a look across the area, most of the lingering showers and
storms have now lifted into northeastern SD and central MN as of
8pm. As stratus builds in overnight, the forecast remains on track
for a line of weakening thunderstorms to traverse the state
overnight leading to additional rain chances for areas north of I-90
by Monday morning. With waning instability and limited shear, severe
weather is not expected. However, pockets of moderate rain will be
possible with any stronger cells especially along the U.S. Highway-
14 corridor. Nonetheless, should see most of this activity gradually
diminish by mid-morning. Looking ahead, its gonna be another warm
day with highs mainly in the 80s to low 90s expected.

Shifting gears here, there are some low confidence (30% or less)
chances for an few isolated showers and potentially a thunderstorm
or two by Monday afternoon as a weak shortwave intersects a
lingering cold/stationary front. However, the uncertainty comes with
the environment. With another High CAPE/Low Shear set up along with
the potential for a decently strong cap according to soundings; the
environment is more conditionally unstable then fully unstable. With
this in mind, we`ll either need stronger forcing to break through
the cap or diurnal heating. Nonetheless, if this can happen; there
will be a narrow window for a stronger storm or two to develop from
late afternoon to early evening with up to golf ball sized hail
being the main concern given the steeper lapse rates (6.5-7.5
degrees C/km). While the threat is lower, can`t completely rule a
few stronger wind gusts up to 65 mph if collapsing thunderstorms can
become more outflow dominant. Otherwise, should see potential taper
down by late evening with the loss of diurnal heating.

&&

.DISCUSSION...
Issued at 247 PM CDT Sun Jun 7 2026

A weak upper level low has pushed into the area this afternoon. This
low is encountering a less stable environment characterized by
instability values around 1000 J/kg of MLCAPE. Deep layer shear will
be quite weak on the order of 10-15 knots. Thus, severe storms are
not expected. Lightning, brief heavy rain, small hail, and gusty
winds up to 30-40 mph are the main hazards. Should see storm chances
diminish this evening as the boundary layer stabilizes. A second
round of showers and some storms remains possible late this evening
an night. These storms will be from a weakening MCS and could clip
locations near and north of highway-14. Should these storms make it
into the forecast area, they will be elevated and not severe given
weak vertical shear in the area.

The previously mentioned weak upper level wave will push northeast
of the forecast area on Monday. This will promote subsidence on its
back side. The morning hours look to be dry while high temperatures
warm to the upper 80s to low 90s by the afternoon. A cold front will
be pushing into the area from the west. This front looks to push
into locations west of the James River tomorrow. This front looks to
serve as a potential trigger for thunderstorms. Questions remain
about this potential though due to capping. Mid level lapse rates
look to exceed 8.0 C/km aloft while forcing for ascent remains weak
to . This will result in a cap right over the front. Latest
REFS shows an ensemble average about about a -60J/kg cap right over
the front. Individual members of the REFS show a variable cap with
some members showing a stronger cap and others showing little to no
cap. Latest HRRR, RRFS, and some of the newer MPAS models do show
convection developing along the front. Thus, confidence is higher in
convection developing than not at this time. Storms look to fire
along the front west of I-29. If the front can progress eastwards
enough, locations west of I-29 but along and east of the James River
may be where most of the storms develop. As of now, these storms
look to be isolated in coverage in an environment characterized by
2,000+ J/kg and effective shear values up to 35-40 knots. This looks
to support multi-cells to potentially supercells capable of large
hail up to golf ball size and damaging winds to 65 mph. Hodographs
are generally straight which would support splitting storms. Larger
hail can be achieved in a left split storm. Some disagreement
remains about an MCS that looks to develop across western Nebraska.
Tough to say how this MCS may track as the latest hi-res guidance is
split on whether this MCS pushes into the forecast area or stays
south along I-80. Will keep an eye on this potential.

Severe storm chances persist through the middle of the week,
beginning on Tuesday. A stronger upper level wave will begin to
eject into the Northern Plains on Tuesday, sending shortwave troughs
out ahead of it. Before storm chances occur, Tuesday will be a hot
day with high temperatures soaring to the 90s to up to about
100F.The ensembles continue to support this as they show a 40-90%
chance for high temperatures to exceed 90F. Dew points will remain
moist in the 60s to even 70s will result decently humid conditions.
A Heat Advisory may be needed for Tuesday as heat indices rise to
near to just above 100F. A second cold front will be working its way
through the Northern Plains on Tuesday, serving as the trigger for
convection. The best forcing for ascent looks to be to the north and
west of the forecast area with the previously mentioned shortwaves.
This seems to be somewhat supported by the RRFS, MPAS-RN model, and
the NAM12km as they show the bulk of the convection in this area.
Despite this, the cold front will be draped across a large portion
of the Northern and Central Plains. So convection may still develop
in or near the forecast area. Tough to say at this time but the
environment supports severe storms should they develop.

Wednesday will also see another chance for strong to severe storms.
The main wave and associated exit region of an upper level jet will
push into the Northern Plains. Despite these favorable features
being in place, questions remain regarding how quickly the
previously mentioned cold front will progress. If the front were to
progress at a faster rate of speed, then severe storm chances could
be lowered if the front is able to push east of the forecast area
before convection develops. If the fronts speed is slower, then
convection could develop on the front in the forecast area. Latest
medium range guidance and ML guidance is in agreement in the front
pushing through the area more quickly. While these trends are
looking better, can`t say for sure that they will continue. If the
front were to slow down and allow convection to develop in the area,
then a line of storm could develop before racing east of the area.
Will keep an eye on the front`s trends over the coming days. Aside
from storm chances, Wednesday will be another hot, although slightly
cooler day with highs warming to the mid 80s to 90s, warmest along
and east of the James River. Similar probabilities remain in the
ensembles of a 40-80% chance for highs to exceed 90F. Slightly lower
dew points look to keep heat indices a little lower, down to the
90s. That said, both Tuesday and Wednesday will see moderate to
major heat risk.

The rest of the week and weekend looks to see a return to near to
slightly above seasonable temperatures with highs lowering to the
70s and 80s. Broad troughing over the northern CONUS could keep rain
chances (20-30%) in the forecast for this period of time. Latest AI
guidance suggests that any chance for severe storms will remain at
15% or less into early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1040 PM CDT Sun Jun 7 2026

Mainly VFR conditions this evening will transition to MVFR to
IFR conditions overnight. Taking a look across the area, patches
of developing stratus are starting to fill into areas east of
I-29 this evening. Expect these developing low clouds to
gradually fill in promoting MVFR to IFR cigs through mid-morning
on Monday. Otherwise, could see a few lingering showers move
into the Highway-14 corridor. With this in mind, added a PROB30
group in for KHON during the morning hours. Looking ahead, additional
showers and thunderstorms could develop across the area this
afternoon. However, there isn`t enough confidence in coverage to
add in weather groups at this time. Lastly, lighter winds are
expected during the day on Monday.

&&

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

&&

$$

UPDATE...05
DISCUSSION...Meyers
AVIATION...05