textproduct: Sioux Falls

KEY MESSAGES

- Patchy drizzle through mid morning will lead to some reduced visibility. Use caution and keep headlights on through the morning commute.

- Showers and isolated thunderstorms return to the area by early this afternoon, continuing through 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. Confidence in this risk is low.

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

UPDATE

Issued at 304 AM CDT Mon May 18 2026

Temperatures this morning range from the mid 40s to the mid 60s from west to east. Lows tonight fall to the upper 30s to mid 50s, although areas west of the James River may stay a bit warmer than the upper 30s if stratus lingers longer into the overnight hours, as some models hint at. Still seeing breezy winds with gusts to 30 mph at times.

Focus shifts to the next wave progged to move out of the Rockies late this afternoon through tonight, as well as the preceding WAA and weak vorticity lobe. Expect scattered showers and isolated thunderstorms to develop this morning across NE and lift northward into our area by the afternoon hours. Showers and isolated storms continue through the evening/overnight hours, tapering down from west to east as the 700mb trough moves across the area.

A few isolated strong to severe storms are possible along and southeast of a line from Wayne to Sheldon to Windom, mainly from 4 to 9 PM. Confidence is low in the chances for severe weather, as there are a few questions. One, how much do skies clear during the day, especially with latest guidance showing stratus remaining in place through the early afternoon? Two, depending on cloud cover, how much can the atmosphere recover from yesterday's storms? Finally, where do any boundaries end up today, and how quickly does the elevated front move east?

If we are able to get a stronger storm or two to develop, hail to ping pong ball size (1.5") and wind gusts to 60 mph are the main threats. If we have a surface boundary or get a surface based storm (more likely if we're able to clear out today), a tornado cannot be ruled out, although risk is low. Heavy rain in thunderstorms may cause some localized flooding issues if storms track over the same areas which received heavy rain over the weekend. Stay aware for possible warnings later today.

DISCUSSION

Issued at 120 PM CDT Sun May 17 2026

The short-term convective outlook presents a highly volatile spring severe weather setup. Latest surface analysis shows a complex pattern, anchored by a strong 994 mb low over northwest KS. An inverted trough extended north of the low through central SD, while a well-defined warm front stretched northeast of the low into east central NE. A weaker low was also noted in north central NE. Visible satellite imagery revealed stable wave clouds advancing northeast over far northeast NE and extreme SE SD, ahead of the advancing warm front. Regional radar imagery showed a complex of strong to severe storms over north central NE. This storm complex is forecast by short range guidance to continue tracking east this afternoon, intensifying as interacts with the richer low- level moisture pool near and south of the warm front.

Moderate to strong instability will be in place over the southern to eastern CWA by late afternoon with MLCAPE nearing 3000 J/kg. In addition, deep layer shear will increase to around 50 kt, coincident with a mid level speed max ejecting from the deep upper trough to our west. As the system evolves over the next several hours, it appears the ingredients for a significant severe weather event will be most favored over the southern to eastern CWA. Ahead of the main convective line, some CAMs show supercell development along the northward advancing warm front. These storms would present a risk of very large hail (2"+) and tornadoes. Given the amount of low level SRH/curved hodographs present, a couple strong tornadoes are possible. The convective cluster currently entering our far southwest CWA should strengthen as it shifts east, with an initial hail and tornado threat transitioning to a damaging straight line wind threat (70+ MPH) as it grows upscale into a squall line/QLCS. Some line-embedded QLCS tornadoes are possible, especially for any line segments that become oriented north/south or northwest/southeast, given southwesterly 0-3 km shear vectors. Timing from latest high-res guidance suggests this activity exits to the east of our CWA late this evening.

Precipitation amounts will vary significantly based on convective tracks, though NBM guidance and HREF probability match mean fields project a widespread 0.50 to 1.50 inches of rainfall, particularly across northwest Iowa and southwest Minnesota. On Monday, the cold front finally pushes into the area. Instability and shear are forecast to be much lower than today, however, there will be a conditional risk of severe storms over the eastern CWA during the late afternoon to evening, if the airmass can destabilize sufficiently ahead of the front. SPC's Day 2 outlook indicates as Marginal Risk (level 1 of 5), for our MN and IA counties.

Behind the departing upper wave, quasi-zonal flow sets up for Tuesday and Wednesday, yielding quiet conditions and seasonally cool high temperatures moderating from the upper 50s Tuesday to mid-upper 60s Wednesday.

The next upper wave moves in for the Thursday to Friday period, however Gulf moisture remains cutoff ahead of this system. Evaluating the ECMWF Extreme Forecast Index (EFI) reveals no significant climatological anomalies for precipitation or wind across the upper Midwest during this period, reinforcing the the idea of a low-impact system for our area. The current forecast sticks closely to the NBM consensus, maintaining broad 20-30 percent probabilities for light rain for late Thursday into Saturday.

By late this week and especially this weekend, temperatures will embark on a steady upward trajectory, as the mid level flow backs west, then southwest. The Climate Prediction Center (CPC) 6-10 day outlook favors above-normal temperatures across the Northern Plains and Upper Midwest, which supports blended guidance high temperatures reaching well into the 80s on Sunday.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 632 AM CDT Mon May 18 2026

MVFR to IFR ceilings persist this morning, and are expected to do so through the period. Lowest ceilings overall are near and east of I-29. Have seen patchy to widespread drizzle this morning with the low ceilings, and guidance is handling this poorly this morning. Have seen visibility also down to MVFR and IFR; drizzle lingers through the mid morning. Showers and isolated storms return to the area by early this afternoon, continuing through this evening. Tried to narrow convective timing as much as possible with latest trends, but expect further refinement. With slightly higher confidence in TSRA potential for northwestern IA, included mention. However, still low enough confidence in timing/occurrence at the terminal to exclude from prevailing group for now.

Winds through the period remain close to northwesterly, with gusts 20 to 30 knots.

A few thunderstorms along/southeast of KLCG-KSHL-KMWM may be strong to severe with large hail and strong winds, but confidence is low.

FSD WATCHES/WARNINGS/ADVISORIES

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