textproduct: Sioux Falls

KEY MESSAGES

- A cool front brings an isolated risk for strong thunderstorms along Highway 20 into north central Iowa early this evening. Large hail and 60 mph winds will be risks. Weaker elevated storms may be possible through 4pm further north.

- Cooler temperatures and lower humidity is expected for the rest of the work week, with temperatures climbing back to the 90s next weekend.

- The majority of this week will be dry, outside of a 30% risk of showers and non-severe thunderstorms Wednesday into Thursday.

DISCUSSION

Issued at 125 PM CDT Mon Jul 20 2026

THIS AFTERNOON: A cool front continues to push southeast through the forecast area early this afternoon. Behind the front, elevated moisture may continue to produce isolated showers or thunderstorms driven by a narrow corridor of vorticity sinking through central Minnesota. This activity is likely to remain elevated as it moves into south central Minnesota. Eventually it may become more surface based as it moves into northern Iowa. Secondary ACCAS or isolated thunderstorms further west into Central South Dakota are expected to continue to struggle southeast. Elsewhere, moisture pooling ahead of the boundary along with thermal compression ahead of the front will push heat index values into the 100s along and south of I-90 this afternoon. Drier air advecting behind the passage of the front should lead to dropping heat index values after 3pm from north to south, with all headlines on schedule to end by 7-8pm.

The southward progression of the boundary will continue into the evening reaching a line from Norfolk to Sioux City To Estherville by 4-5pm. Soundings along the boundary continue to look very capped, with much less forcing generally expected over the front. It's the ACCAS over central SD that we'll need to keep an eye on early this evening, as it does have some potential to intensify slightly as it reaches Highway 20 and could become surface based. IF upscale growth could happen, the combination of shear and instability could signal some golf ball sized hail and 60 mph winds. Again though, this looks like a VERY limited area in time and space this evening.

TONIGHT: Dew points will crash overnight, signaling a return of cooler and drier air. Overnight lows may fall well into the 60s by daybreak Tuesday.

TUESDAY: A beautiful day is anticipated on Tuesday with Canadian high pressure sinking southward. High temperatures only in the upper 70s to lower 80s with dew points in the 50s will signal a great.

WEDNESDAY-FRIDAY: The semi-northwest flow through the second half of the week will keep cooler temperatures in the region through the rest of the week. Highs are expected to reach the lower 80s each day. A weak perturbation in this flow pattern leaves the Central Rockies early Wednesday. Most guidance tracks this wave through Nebraska, but a few solutions could bring light rain risks into mid- day Wednesday along and west of the James River valley. A second wave arrives by Thursday night into Friday, but again, uncertainty in track keeps the risks for any precipitation less than 30% in most locations along or west of I-29.

SATURDAY-SUNDAY: We'll again see rising temperatures by next weekend, as confidence is high in an expanding mid-lvl ridge through the Plains. This ridge however will be more suppressed than the one that has just left the region, signaling a shorter surge in temperatures to the 90s/100s, but also allowing a ridge rider or two to move through the Plains by the end of the weekend.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1207 PM CDT Mon Jul 20 2026

Frontal boundary continues to push southeast early this afternoon. Behind the boundary mid-lvl moisture AOA 8-10K ft will passes through the TAF locations. Isolated showers or lightning could be possible, however risks remain minimal. Once this mid-lvl cloud layer passes, clear skies and breezy northwest winds will continue into the overnight.

Greatest risks for any severe convection may end up focused along and south of Highway 20 this evening, though this activity may stay very isolated.

VFR conditions and clear skies are likely at all locations after 10pm this evening and into Tuesday morning.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory until 8 PM CDT this evening for SDZ050-063>069. Extreme Heat Warning until 8 PM CDT this evening for SDZ070- 071. Heat Advisory until 4 PM CDT this afternoon for SDZ061-062. MN...Heat Advisory until 4 PM CDT this afternoon for MNZ080-081-089- 090-098. IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003- 012>014. Extreme Heat Warning until 8 PM CDT this evening for IAZ020>022-031-032. NE...Extreme Heat Warning until 8 PM CDT this evening for NEZ013- 014.