331
FXUS63 KFSD 191146
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
646 AM CDT Sun Jul 19 2026

.KEY MESSAGES...

- Hotter conditions return this afternoon and likely on Monday
  where heat indices could climb into the 90s and low 100s for
  parts of the areas.

- A Heat Advisory remains in effect from 1PM to 9PM for areas
  along and west of the James River.

- Scattered showers continue this morning mainly west of I-29.
  Additional chances for showers and storms will be possible
  this evening and on Monday with the potential for a few
  stronger storms.

&&

.UPDATE...
Issued at 400 AM CDT Sun Jul 19 2026

Taking a look across the area, we`re continuing to watch scattered
showers with isolated thunderstorms develop across northcentral SD
this morning mostly in response to a weak wave intersecting a
nocturnal LLJ. While we`re still on track for this developing
activity to move into areas west of I-29 this morning, we`re still
expecting this activity to gradually weaken with east-southeastward
progression mainly due to a more stable airmass overhead. Should see
most of this activity dissipate by late morning into early
afternoon. Otherwise, the main focus will be on the heat as
southerly surface winds and a lifting warm front help temperatures
peak in the mid 80s to upper 90s this afternoon.

This combined with dew points in the 60s to low 70s should lead heat
index values in the 90s to low 100s. With the warmest conditions
expected along and west of the James River Valley, our heat advisory
should be in great shape. Nonetheless, a scattered cloud deck with
this morning`s activity could affect our temperatures this afternoon
so we`ll have to watch and see. Lastly, additional showers and
thunderstorms will be possible starting this evening. While the
overall severe risk is low, IF a stronger storm manages to develop;
wind gusts up to 65 mph will be the main concern with the focus
being along the Missouri River Valley.

&&

.DISCUSSION...
Issued at 201 PM CDT Sat Jul 18 2026

Quiet conditions continue this afternoon with highs warming up to
the 80s. Winds remain light out of the east/northeast, making for a
pleasant Summer day. Light concentrations of smoke remain across the
area. Sensitive individuals could have some issues with the smoke
across the area. With the light winds in place, the light smoke
looks to be here to stay. Dry conditions will persist through the
rest of today but things will change for the overnight hours. A cold
front that has passed through the forecast area this morning will
begin to return northwards as winds turn to out of the south. This
will mainly affect the elevated front between 850 to 700 mb as the
warm air advection (WAA) associated with this southerly flow looks
to develop elevated convection along this boundary. Mean flow will
be parallel to the boundary, resulting in any storms that form to
travel down this boundary. Instability looks to be on the weaker
side with CAPE values only up to around 500 to 700 J/kg. Effective
shear values are also weak on the order of 30 knots or less. Thus,
these storms are not expected to be strong to severe, but drier air
in the low levels could result in a few brief wind gusts and perhaps
small hail. The storms look to develop across central South Dakota
tonight before sliding southeastwards along the boundary into the
forecast area. Instability values will be waning as they enter the
forecast area, so they are expected to be weakening with
southeastward extent.

Sunday will be the warmest day this weekend as the thermal ridge
continues to push eastwards. High temperatures look to warm to the
mid 80s to about 100F with the warmest temperatures occurring along
and west of the James River Valley. With a return to southerly flow
in place, slightly higher dew points will be advected into the area.
Dew points look to moisten to the 60s to potentially reaching 70F in
a few locations. This will push heat indices up to the 90s to low
100s across the bulk of the area. The highest heat indices will
occur with the hottest temperatures along and west of the James
River Valley. As such, a Heat Advisory has been issued for this area
from 1PM to 9PM. Aside from the heat, a few showers could persist
into the morning hours before dissipating by the afternoon
timeframe. Otherwise, the rest of the afternoon hours look dry.
Light concentrations of smoke look to persist across the area
despite the southerly flow. The dry conditions will not last long
though as another chance for showers and storms look to make a
return to the area Sunday night. A shortwave trough will push out of
North Dakota and dive southeastwards. This looks to being shower and
storm chances to mainly southwest Minnesota at this time. The
previously mentioned boundary will continue to return northwards,
serving as the focal point for this new round of convection to
develop on. Currently, it seems like the storms will develop along
the 925mb front and track down it through the night. Vertical shear
will be stronger but instability values look to remain on the weak
side of things with a magnitude between 500 to 1000 J/kg. Thus,
isolated severe storms are possible across mainly southwest
Minnesota Sunday night with large hail and damaging winds as the
primary hazards.

The core of the thermal ridge will finally make its way over the
forecast area on Monday. This will push high temperatures all the
way up to the mid 90s to low 100s. With sufficient moisture
remaining in the area, heat indices will reach up to the 90s to low
to potentially reaching up to about 104 to 105F. The hottest
temperatures and heat indices will occur along and south of I-90.
Some uncertainty remains regarding these hot temperatures as a
second round of thunderstorms is possible Monday afternoon. A cold
front will be pushing through the area after the first round of
showers and storms passes through the area Monday morning. This
front looks to result in a second round of showers and storms Monday
afternoon. As of now, it looks like storms could develop east of I-
29 at this time. If they do form, they will again have the potential
to be strong to severe. There is uncertainty regarding where storms
develop as well as if these storms may affect afternoon highs enough
to limit diurnal heating potential. Heat headlines may be needed but
that decision will be made once confidence increases in storm
coverage, location, and temperatures.

Much drier air is in store behind the previously mentioned cold
front. High temperatures will return to near seasonable for the rest
of the work week with highs in the 80s. A few chances (15-35%) for
rain are possible throughout the week but details are uncertain at
this time. Temperatures may trend back to above average by next
weekend as zonal flow returns aloft.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 640 AM CDT Sun Jul 19 2026

Mainly VFR conditions with occasional MVFR conditions are expected
this TAF period. Taking a look across the area, scattered showers
with isolated thunderstorms continue to develop across central
SD this morning. Should see this activity progress into our area
between 12z-14z bringing the potential for MVFR vsbys to KHON
and potentially KFSD. Decided to add a PROB30 group to KHON.
However, confidence is not high enough to add something to KFSD
yet. Addtional showers and thunderstorms will be possible this
evening mainly along the Missouri River Valley. With this in
mind, decided to add a PROB30 group to KSUX for the increased
probabilities. Otherwise, southerly surface winds will become
marginally breezy this afternoon with gusts between 15-25 mph
possible through this evening.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM this afternoon to 9 PM CDT this
     evening for SDZ038-050-052-053-057>060-063>065-068-069.
MN...None.
IA...None.
NE...None.

&&

$$

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