textproduct: Sioux Falls

KEY MESSAGES

- Pockets of light to moderate rain will continue through this evening mainly along and north of I-90. Any additional accumulations should be at a 0.10" of an inch or less.

- Areas of frost or freeze will be possible by Wednesday morning, with the better chances north of I-90. Make sure to cover/bring in any sensitive vegetation.

- Cooler conditions will prevail this week. Dry weather expected mid week. Another round of storms will be possible from Thursday through Friday.

UPDATE

Issued at 910 PM CDT Mon May 18 2026

While the main severe risk has now pushed east of our area this evening, scattered light to moderate showers will likely persist into the late evening as a mid-level wave lifts through eastern SD and central MN tonight. Given the waning mid-level saturation and lower cloud heights according to sounding, can't rule out a few pockets of drizzle through Tuesday morning as well. While this could lead to persistent dreary conditions overnight, any accumulations will likely be on the lower side with another 0.10" of an inch or less expected for most areas. Otherwise, should see cloud cover begin to gradually clear from west to east starting by Tuesday morning. With lingering cold air advection (CAA) aloft and breezy northwesterly winds at the surface, expected another cool day with highs mainly in the low to upper 50s. With this in mind, make sure to take a jacket when heading out on Tuesday as the cooler and breezier conditions could make things feel a bit chilly at times especially during the first half of the day.

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 /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 636 PM CDT Mon May 18 2026

Mainly IFR to LIFR ceiling and vsbys continue this TAF period. Taking a look at satellite imagery, we're continuing to see scattered showers and thunderstorms develop east of I-29. While these conditions will likely persist into the evening, should see things transition to mainly MVFR to IFR cigs as the lower ceilings continues to produce pockets of drizzle. Otherwise, breezy northwesterly winds will continue into the overnight to end the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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