textproduct: Sioux Falls

KEY MESSAGES

- Near to slightly below normal temperatures prevail through the end of the week. A couple passing shower and storm chances linger through the end of the week as well.

- Growing confidence in an extended period of heat and humidity beginning Sunday into next week. Heat and humidity could bring very low probabilities for thunderstorms each day.

- A low chance for strong to possibly severe thunderstorms Saturday night into Sunday morning and again Monday into Monday night. For now, the greatest risk remains off to the west and north of the area.

UPDATE

Issued at 254 AM CDT Thu Jun 25 2026

Forecast remains on track this morning.

High clouds are increasing from the southwest, but expect conditions to stay dry with the best moisture across NE. Fog chances look low (less than 20%) early this morning with slightly higher winds and dew point depressions. If fog develops, would expect it to be patchy and shallow. We'll start today in the 50s. A pleasant and slightly cooler than average day on tap today with increasing clouds and highs in the 70s.

Enjoy these cooler temperatures as confidence continues to increase in the potential for possibly dangerous heat Sunday into early next week. 25.00z ensemble probability of highs exceeding 90 degrees are increasing and expanding across the area, with 50-90% chance Sunday and/or Monday. HeatRisk climbs in to the Major and possibly Extreme categories, with heat index values near 105. Current forecast values approach record warm highs and lows for Sioux Falls (Monday) and Sioux City (Sunday and Monday). Plan ahead to reduce risk of heat illness this weekend into early next week, especially if you are planning to spend time outdoors.

DISCUSSION

Issued at 105 PM CDT Wed Jun 24 2026

A very weak wave in southwest SD will drift through far southeast SD and northern NE late this afternoon into the evening. Model soundings indicate some weak elevated instability with some fairly dry air below this more moist, slightly unstable layer. This may allow a few wind gusts to 40 mph if the showers can develop. Overall this threat should come to an end by about 11 pm.

Thursday should prove to be a very pleasant day with light northerly winds and highs in the 70s.

Upper level troughing begins to develop to the west on Friday which will turn winds more to the southeast and become a bit more gusty. Expecting more widespread high temperatures into the 80s. Overall dry conditions are expected but some elevated weak instability in the mid level could bring some showers to areas west of the James River late Thursday night into Friday morning.

Saturday should prove to be dry as well, although a very weak wave will move north through central SD and could bring some isolated showers to that area. Low level moisture continues to increase ahead of this troughiness to the west, which will increases the instability through the day. However, at this time some strato cumulus is expected to be in place for a good chunk of Saturday which will likely lead to a significant capping inversion.

Saturday night may prove to be our better chance for severe weather, especially west of I-29. For now the better chances look to be northwest of the area, but given the strength of the wave to the west, the strength of the LLJ and the very deep instability, will need to watch out for an MCS to build southeast into the area.

Once this LLJ barrels north on Sunday, the chances for showers and storms should stay mainly north of the area. Sunday will be the first hot day with highs into the 90s and heat indices likely between 95 to 105.

Hot and potentially humid conditions will build into the area through much of next week. Faster southerly flow aloft will remain over parts of central SD, which may allow for an occasional chance for showers and storms as well as cloud cover, so west of I-29 will see a better chance to come up short on high temperatures at times, while near and east of I-29 will likely see the better chances for these hotter conditions with lower chances for showers and storms.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 611 AM CDT Thu Jun 25 2026

VFR conditions prevail through the period, with mid and high clouds. Winds remain light and mostly variable, becoming more easterly to southeasterly toward the end of the period. Scattered showers move into the James River Valley overnight into early Friday, and have added a mention via PROB30 for KHON at this time. Could see some very patchy MVFR conditions with this activity, but confidence is too low to include for KHON.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.