textproduct: Sioux Falls

KEY MESSAGES

- Showers and isolated thunderstorms return to the area this afternoon this evening into tonight.

- A few storms along and southeast of a Wayne to Sheldon to Windom line may be strong to severe late this afternoon into this evening. The main threat would be hail to half dollar size but storms this strong should remain very isolated and likely closer to near and east of Highway 60.

- Areas of frost or freeze will be possible on Wednesday morning, with the better chances north of I-90.

- Cool conditions prevail this week. Dry weather expected mid week. Another round of storms is possible Thursday through Friday.

DISCUSSION

Issued at 1258 PM CDT Mon May 18 2026

Early this afternoon the surface to 925 mb front was across southern NE into southern IA. Given the marginal strength of the incoming wave, this boundary should not lift far enough north and west by late afternoon to get into the area. This should limit any wind and tornado threats and keep them off to the southeast. However, some elevated hailers will remain possible across mainly northwest IA as elevated CAPE values ramp up to about 1000-1500 J/KG and deep layer shear is a fairly strong, unidirectional 40-50 knots. This would be lifting a parcel from above the stratus layer, which would likely be in about the 800-750mb layer. The better chances will be from about 5 pm to 9 pm.

After this wave pushes the remaining instability out of the area this evening, dry and cool conditions are expected for Tuesday and Wednesday. The only concerns on these two days will be the potential for frost and freeze conditions, mostly north of I-90, as surface high pressure is in place. Another weaker wave moves through the area on Wednesday but for now this appears to bring mainly mid level cloud cover.

The next better chance for showers and thunderstorms will come Thursday night into Friday night. At this time severe weather looks to remain isolated as model instability fields are hinting at 1000 J/kg CAPE or less for the most part.

Once this wave passes a warming trend should move in as flat ridging aloft develops ahead of a deepening low pressure in the Northern Rockies. Saturday should be mild, likely in the 70s, while Sunday sees the better chance to warm into the 80s.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1243 PM CDT Mon May 18 2026

Widespread stratus, mai.nly IFR but occasionally MVFR, will persist through much of the night, but gradually improve later tonight into Tuesday morning. Scattered showers and isolated thunderstorms will increase in coverage through the afternoon into the early evening, then gradually diminish through the early overnight hours. The strongest thunderstorms will be in parts of northwest IA, with the better chance from 5 pm through 9 pm. A few of these storms could contain hail.

FSD WATCHES/WARNINGS/ADVISORIES

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