411
FXUS63 KFSD 190349
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1049 PM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Scattered showers with isolated thunderstorms will continue
  through the early evening with the primary hazard being
  locally heavy rainfall.

- A few stronger storms may be possible between Thursday night
  to Friday morning. However, uncertainty remains in
  coverage/location of potential storms.

- Dangerous heat likely returns over the weekend with high
  reaching the upper 90s to low 100s. With heat indices between
  100-110 degrees expected through Sunday, make sure to stay
  hydrated and limit prolonged outdoor activities where
  possible.

&&

.DISCUSSION...
Issued at 304 PM CDT Wed Jun 18 2025

CURRENTS & TONIGHT: Taking a look across the area, scattered showers
with isolated thunderstorms continue across the area this afternoon
mostly in response to increasing dPVA with a progressing mid-level
wave. While an isolated stronger storm isn`t completely out of the
question, the main focus continues to be on the locally heavy
rainfall potential as slower storm motions and higher PWATs promote
a few locally heavy downpours. Since this development is mostly
diurnally driven, not expect much of this activity to last past the
early evening before gradually dissipating. Lastly, overnight
temperatures will decrease into the upper 50s to low 60s.

THURSDAY & FRIDAY: Looking into the latter parts of the week, the
focus continues to be on the severe weather chances and building
heat. Starting on Thursday, a predominantly ridging pattern will
settle in across the plains keeping things mostly quiet during the
day. With southerly winds and increasing mid-level warm air
advection (WAA), expect temperatures to trend warmer with highs top
out in the upper 80s to mid 90s with the warmest conditions along
and west of Highway-81. As a nocturnal LLJ strengthens and mid-level
wave rides the ridge into our area by Thursday night, scattered
showers with isolated thunderstorms could develop east of I-29
mostly across southern MN. While there still remains some
uncertainty regarding coverage/location, can`t completely rule out
an elevated stronger storm or two given 700-1200 J/kg of instability
and 35-45 kts of bulk shear ahead of the wave. However, the window
for any stronger storms would be fairly limited to 03z-09z (10pm to
4am) given the progressive nature of the system. Nonetheless, large
hail and stronger wind gusts will be the primary hazards with any
stronger storms before they push eastwards to start the day on
Friday.

From here, the focus turns towards the heat as another push of mid-
level WAA along with increasing southerly winds during the day on
Friday leads to building heat across the region. With most ensemble
guidance showing +24 to +30 degrees C (top 1% of climatology) at
850 mb, expect our temperatures to continue to increase with highs
topping out in mid to upper 90s and lower 100s on Friday. With heat
indices between 100-108 degrees possible during the afternoon
hours, decided to issue an area-wide excessive heat watch from
Friday afternoon through Saturday evening. As we get closer to the
weekend, we`ll likely transition this to an advisory or warning as
necessary so make sure to make sure to keep an eye on the forecast!
Lastly, make sure to stay hydrated and to limit outdoor activities
wherever possible.

SATURDAY ONWARDS: Heading into the extended period, the main focus
on Saturday and Sunday continues to be the heat. Similar to Friday,
southerly surface flow and increasing mixing will continue to lead
to dangerous heat for the rest of the rest of the weekend. We`ll
continue to hover around the top 1% to Max of climatology for
temperatures according to the ESAT tables so highs will continue to
hover around the upper 90s to low 100s temperature-wise with heat
indices potentially up to 110 degrees or more. As far as heat
concerns go, Saturday will likely be the better day for more
widespread concerns with temperatures starting in the low to mid 70s
to start the day which could be record breaking. Nonetheless, with
the hot and humid conditions expected to continue throughout the
day; make sure to stay hydrated and inside whenever possible.

By Sunday, portions of the thermal ridge will shift eastwards aloft
as a cold front gradually pushes across the central portions of
SDAK. While the abnormally warm temperatures will continue with
highs expected to peak in the low to upper 90s and low 100s during
the day, the more dangerous heat should be confined to far
southeastern SD and northwestern IA where heat indices up to 105
degrees C are expected. Given the potential, could see additional
heat headlines by Sunday afternoon in the previously outlined areas.
Lastly, as a mid-level wave rides the ridge into our area by Sunday
night; shower and thunderstorm chances will increase and continue
into Monday. From here, a developing rex block over the eastern
CONUS will keep us in southwesterly flow for the majority of the
week promoting periodic shower and thunderstorm chances.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1047 PM CDT Wed Jun 18 2025

VFR conditions are expected through much of the period, with the
only uncertainty coming from potential storm development
Thursday afternoon and then overnight into early Friday. The
better chances (30-40%) for storms will come during the
overnight hours tomorrow night, but look to stay northeast of
the TAF sites into Minnesota at this time. Much greater
uncertainty occurs for any afternoon and evening convection
across mainly South Dakota, with guidance all over the place in
this regard. Current thinking is that any storms that do develop
during this time will be very isolated in nature, and thus have
opted to keep out mention of TS for KHON and KFSD at this time.

Winds will be mostly light and variable tonight, with winds
increasing throughout the day on Thursday out of the
south/southwesterly direction. Highest gusts will be between 20-25
kts, with those highest gusts in south-central South Dakota. After
sunset tomorrow, the low-level jet will ramp up and cause low-level
wind shear concerns to end the period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Extreme Heat Watch from Friday morning through Saturday
     evening for SDZ038>040-050-052>071.
MN...Extreme Heat Watch from Friday morning through Saturday
     evening for MNZ071-072-080-081-089-090-097-098.
IA...Extreme Heat Watch from Friday morning through Saturday
     evening for IAZ001>003-012>014-020>022-031-032.
NE...Extreme Heat Watch from Friday morning through Saturday
     evening for NEZ013-014.

&&

$$

DISCUSSION...05
AVIATION...Samet