textproduct: Sioux Falls

KEY MESSAGES

- Pockets of drizzle and isolated showers continue early this morning. Sprinkles are possible this afternoon across soutwestern Minnesota.

- Frost and freeze conditions are expected tonight into early Wednesday morning across the area - take precautions to protect sensitive vegetation. Frost/Freeze headlines go into effect late tonight.

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

UPDATE

Issued at 301 AM CDT Tue May 19 2026

An area of showers/sprinkles is moving south into the James River Valley early this from northeastern SD. Additionally, drizzle has continue to taper off, despite most of the area under low stratus. Stratus continues through the day, with highs only warming into the 50s once again. May see some diurnally driven sprinkles for southwestern MN and adjacent areas of SD and IA today as we have a bit of weak instability in the saturated stratus layer.

Other change for the next 24 hours was the issuance of Freeze Warnings and Frost Advisories for tonight into early Wednesday morning. Clearing skies with the surface high pressure sliding overhead and light winds late Tuesday through early Wednesday should allow for efficient radiational cooling. We'll also see at least weak CAA at 925mb through the night. We probably won't be as efficient as a couple weeks ago thanks to recent rainfall, but think that temperatures still fall low enough into the 30s to lead to widespread impacts to vegetation. Freeze Warning was limited to the SD side of the US Hwy 14 corridor and into central SD, where confidence is higher in lows falling into the lower 30s.

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1158 PM CDT Mon May 18 2026

Mainly MVFR to IFR conditions will continue this TAF period. Taking a look at satellite imagery, areas of MVFR to LIFR stratus continue to blanket the area with a few pockets of drizzle. While these conditions will likely persist in the overnight hours, should see gradual improvements from west to east by mid-morning on Tuesday returning things back to VFR conditions. Lastly, breezy northwesterly winds will persist intermittently through Tuesday evening to end the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Frost Advisory from 1 AM to 8 AM CDT Wednesday for SDZ050- 054>071. Freeze Warning from 1 AM to 8 AM CDT Wednesday for SDZ038>040- 052-053. MN...Frost Advisory from 1 AM to 8 AM CDT Wednesday for MNZ071-072- 080-081-089-090-097-098. IA...Frost Advisory from 1 AM to 8 AM CDT Wednesday for IAZ001>003- 012>014-020>022-031-032. NE...Frost Advisory from 1 AM to 8 AM CDT Wednesday for NEZ013-014.