textproduct: Sioux Falls

KEY MESSAGES

- A potentially significant severe weather threat is currently developing. Initial storms bring a large hail threat toward central South Dakota and Nebraska in the evening, transitioning to damaging winds potentially in excess of 80 mph farther east into the night. Isolated tornadoes are possible.

- The main timing for strong to severe storms is between 9 pm and 3 am tonight. The peak window for 80+ mph wind gusts is 10 pm to 2 am. These kinds of winds could produce tornado-like damage, so make sure to have multiple ways of receiving weather alerts that can also wake you up in the middle of the night!

- The threat for severe weather continues to trend east of the area Wednesday afternoon. However, can't rule out a stronger storm near and south of Highway 20 early Thursday morning, though uncertainty of severe potential remains high.

UPDATE

Issued at 856 PM CDT Tue Jun 9 2026

Thunderstorms have developed across southern Nebraska, western into central South Dakota, and central North dakota. These storms are beginning to grow upscale, mainly across the Dakotas this evening. Am expecting this line of storms to continue to push east/northeast as the storms should follow close to the mean wind and storm motion vectors. Another round of storms has developed across southern and central Nebraska. These storms are more discrete than the storms in the Dakotas but pone storm in southern Nebraska has produced very strong winds with it, with a peak gust up to about 85 mph. This storm has produced an outflow boundary that new convection is developing on. Think the new convection that can be generated on the outflow boundary could merge into the western line of storms. Thus, it still looks like a line of storms will move through the area tonight. If cells can remain semi-discrete perhaps on the southern end of the line or a new cell develops just ahead of the line, then large hail up to 2 inches or larger is possible. 0-7km theta-e difference values down to about -25K and 0-10 km shear values up to 45 to 50 knots will support a severe line of storms with damaging winds up to 80+ mph winds. The low level jet (LLJ) is expected to strengthen up to about 40 knots this evening and night. The LLJ will expand low level hodographs and increase low level shear profiles. 0- 3 km shear will strengthen up to about 30 knots and be oriented mainly perpendicularly to the line, thus supporting the chance for a few tornadoes. These storms will push through the area beginning after 02z and persist through 07z to 08z before they finally push through the area.

The cold front responsible for these storms remains on track to quickly race eastwards through the area tomorrow. The bulk of any new severe storms that develop on or ahead of this boundary look to be to the east of our area. A few elevated storms are possible behind this boundary Wednesday afternoon and evening though these storms are not expected to be severe. Wednesday will remain a hot day despite the front coming through with highs warming to the 80s and 90s, hottest east of I-29. There could be another round of strong to severe storms late Wednesday night into Thursday morning. Where these storms may form is a bit uncertain but for now it's looking to be near or south of highway-20. Pattern recognition suggests that these storms could develop due to gravity waves. Since these storms will be elevated large hail and damaging winds will be the primary hazard.

DISCUSSION

Issued at 315 PM CDT Tue Jun 9 2026

A hot and humid day continues across the area as temperatures have soared into the 90s with heat indices in the middle 90s so far, though starting to see some spots into the upper 90s to around 100 in parts of northwest Iowa. The Heat Advisory remains in effect until 9 pm for areas near and south of I-90, so continue to stay hydrated out there! Seeing some areas of CU develop across the area this afternoon, and with plenty of instability in place and the heat eroding the cap, can't rule out a stray shower or thunderstorm through the afternoon. The 09.12Z REFS ensemble is the most excited about this as it shows 20-40% chance of hourly measurable precipitation this afternoon over southwest Minnesota, but this remains an outlier and so the official forecast calls for a less than 15% chance of rain as there won't be much upper level support to get storms going. But if a storm is able to develop, then large hail up to ping pong ball in size will be possible given steep mid level lapse rates and effective bulk shear on the order of 40-45 kts.

A potentially significant severe weather threat is in store for the area tonight. A negatively tilted trough will move into the northern Plains tonight as a cool front approaches the area. Ahead of this, a highly unstable atmosphere will be in place, with guidance showing 2,500-3,500 J/kg of CAPE available despite the loss of daytime heating. Two areas of storms look to develop late this afternoon, one over western South Dakota and one over central Nebraska. The first area will lift mainly northeast of the area through this evening, but could clip the Highway-14 corridor near and west of the James River. Most of the 09.12Z guidance kept the greater chances north of the area, though some of the latest HRRR runs have trended a bit farther south. If this were to clip our area, look for this to happen between 10 pm and 1 am. Damaging winds to 70 mph would be the main threat with this activity, though large hail up to golf ball in size will be possible as well. Can't rule out a tornado given the low level curvature of the hodographs, but storms will likely be becoming more elevated with time through the evening, diminishing the tornado threat, but not reducing it to zero as storms move through.

The second area to watch that develops over central Nebraska has the better chance of becoming the "main show" so to speak regarding the severe weather threat. Storms that develop in this area will quickly lift north-northeast and form into a line or a couple of linear clusters as they quickly swing through the area. This activity will likely cross the Missouri River around 10 to 11 pm, move across the I-90 corridor around midnight, and exits out of our southwest Minnesota and northern Iowa counties by 2 to 3 am. Guidance continues to be consistent in bringing in the strongest winds with this activity, likely owing to the greater instability. This is where we could see gusts as high as 80 mph or slightly higher, bringing the potential for destructive straight-line winds. Not expecting widespread 80+ mph gusts given the weaker shear, but widespread 40-60 mph winds look likely depending on how many individual clusters end up developing. Mid level lapse rates will be around 7.5-8 C/km and large CAPE profiles will also promote hail potentially to the size of 2 inches or slightly larger as the storms cross the Missouri and are more isolated, and then up to golf ball in size as storms turn more linear. Guidance shows the better south- southwesterly low level jet of up to 40-45 kts developing south of I- 90 and into northwest Iowa and far northeast Nebraska, so will have to watch for a tornado or two, though the elevated nature of the storms will tend to limit this threat overall.

Some limiting factors other then the weaker bulk shear than compared to areas to our north, will be the fact that some soundings, particularly the 09.12Z NAM, show a warm layer around 750 mb that could limit some storms from forming. The warm layer is fairly shallow though, but still could put a stop to at least some of the storms developing. Even with this, that warm layer does erode on that NAM run over northwest Iowa, so storms still go off there if this run ends up coming to fruition. But still, if that warm layer ends up being stronger than expected, this could put a dent into thunderstorm chances. Either way, be sure to remain weather aware tonight and make sure to have multiple ways of receiving alerts that can also wake you up in the middle of the night. Also keep in mind that if any storm produces 80+ mph straight line winds, this could do similar damage to tornadoes, so know where your tornado safe place is even though the tornado threat is low.

Not much time to look into the forecast after tonight's event, but the severe weather threat continues to trend farther east for Wednesday afternoon due most guidance moving the cool front east of the area by peak daytime heating. Will have to watch early Thursday morning as the main wave moves through as around 50-60+ kts of bulk shear develops with this. Current indications is that the best instability will be pushed south of the area as this wave moves through, but folks near and south of Highway 20 will need to stay up to date with the latest forecast in case greater instability trends north. Otherwise, look for generally cooler temperatures heading into early next week.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 620 PM CDT Tue Jun 9 2026

Mainly VFR conditions with occasional MVFR to IFR conditions will be possible this TAF period. Taking a look at satellite imagery, mostly clear conditions continue this evening as a "Cue" field begins to build across the Missouri River Valley. Should see the quieter conditions continue over the next few hours before scattered showers and thunderstorms progress across the area this evening. Decided to continue the trend of adding TEMPO groups in for both KFSD & KHON since that is where we're most confident. However, decided to also add in PROB30 group into KSUX with the potential for lingering showers to move through that area. Otherwise, breezy southerly winds will continue well into the overnight hours before westerly winds return by late Wednesday morning

FSD WATCHES/WARNINGS/ADVISORIES

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