textproduct: Sioux Falls

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.