textproduct: Sioux Falls

KEY MESSAGES

- Portions of southeast South Dakota and southwest Minnesota will see a level 2 of 5 risk for severe storms late this afternoon and evening, with lesser risks farther east and south. Large hail and damaging winds are the primary threats, with an isolated tornado also possible.

- Some agreement on the better chance for scattered thunderstorms containing heavy rain to be generally near highway 14 later today into tonight. Confidence is fairly low however as there are quite a few differences across many models.

- Heavy rain, roughly 2-5 inches, fell across parts of Hamlin and Deuel Counties yesterday evening. Will have to see what affect this has on the Big Sioux River in Brookings County, possibly coupled with additional rainfall today and tonight.

- While details are far more uncertain, an isolated to scattered severe storm risk will linger into Friday. The greater risks at this time shift southeast into eastern Nebraska, Iowa and far southern Minnesota.

- Temperatures remain in the 80s through the week and rise towards the low 90s by the end of the weekend.

UPDATE

Issued at 258 AM CDT Thu Jun 4 2026

The right entrance region of the upper level jet will exit the area through the afternoon. This will bring a weak wave to NE into northwest IA by afternoon and could maintain and area of showers and thunderstorms through the day over parts of northeast NE and northwest IA. This will keep showers and thunderstorms over these areas through the day into tonight. For now these storms should not be severe or at least any severe weather will be very isolated. To the north clearing is expected today with instability expected to build through mid to late afternoon. Still some details to work out on just where the lower level boundary will be, but a wave is expected to move into central and northern SD this afternoon and evening. Ahead of this wave southerly flow will increase a bit, with the the 925-850 mb warm front expected to set up somewhere close to highway 14. While deeper layer shear will only be on the weaker side, roughly 30 knots, CAPE values will climb to 1500-2000 J/kg. This should support a few strong updrafts with hail to the size of ping pong balls and wind gusts to 65 mph. However, with freezing levels about 11.5-12 kft and possible training of cells heavy rain may become a threat. The latest GEFS and Canadian ensembles are pointing towards a good chance (30-40 percent) of more than an inch of rain near and north of highway 14. The 6z HRRR, 0z RRFS and 0z WRF ARW all point to this location as well with pockets of 2-4", so will need to keep a close eye on where everything sets up Thursday afternoon. The KFSD radar indicates a solid core of 3-5" of rain just north of Brookings county with 1-3" of rain across northern parts of Brookings county into northern parts of Lincoln and Lyon counties in MN as well.

DISCUSSION

Issued at 304 PM CDT Wed Jun 3 2026

An active few days are in store for the region beginning this afternoon as an upper trough located over Alberta sends several waves through the region. Through the day today a deep, warm layer of moist air will advect into the region from the south. Highs will climb into the 80s with dew points in the mid 60s. Plentiful instability (1500-2500+ J/kg) will build into the region ahead of an approaching cold front. This combined with steep low and mid-level lapse rates, an increasing LLJ, veering winds aloft (clockwise hodographs), in addition to strong divergence aloft set the stage for isolated to scattered strong to severe supercell thunderstorms to form over central South Dakota late this afternoon. Low LCL to LFC heights, increasing helicity and vorticity advection, and favorable shear profiles (initially perpendicular to the front) indicate that tornados may be possible with initial supercell formation. One or two of those tornadoes could be strong, as indicated in the SPC Day 1 Outlook Slight Risk (level 2 of 5). In addition, large hail up to 2+ inches and damaging wind gusts up to 70 mph are possible. CAMs guidance varies a bit in timing of initialization, but most likely it will be between 4-6 pm. Storms will progress eastward through the evening and overnight. As shear becomes more parallel to the front, expect that storms will grow upscale into a quasi-linear system with one or more bowing segments. The threat will then transition to damaging wind gusts, however a few brief spin up tornado along the leading edge and hail remain possible. Timing of storms entering the I-29 corridor region again varies based on guidance, but in general between 10 pm and midnight. Storms should then weaken as the move east, exiting by early to mid-Thursday morning. As far as rain totals go, a quarter to three quarters of an inch is possible. With a few isolated areas seeing up to 1+ inches. Widespread flooding is not expected, but areas that have seen recent rains may experience isolated flooding.

Thursday will be similar in that another deep layer of moisture rich, warm air will advect north into the region during the day. While highs may be limited slightly due to lingering clouds, they are still expected to reach convective temperatures in the 80s. With dew points climbing into the upper 60s and low 70s, it will be another humid day. With the moisture comes renewed instability. Dynamic parameter's are all sufficient again for strong to severe storm development as outlined in SPC Day 2 Slight Risk (level 2 of 5). The difference Thursday will be that two areas of development will be possible, and one may impact the other. The first over northwest Iowa where WAA looks to trigger showers and thunderstorms in the late afternoon and evening. This northward push of warm air pushes against a southeastward advancing cold front, causing it to stall out. As we continue into the evening, storm initiation will occur as upslope flow encounters the stalled front. With a similar dynamic setup as today, strong to severe thunderstorms are once again possible. Large hail and damaging wind gusts will be the primary threats, however tornadoes will also be possible at storm initiation. Overnight storms will grow upscale into a line with wind becoming the primary threat.

Friday will be another day of increased risk for strong to severe thunderstorms. However, this round will be highly dependent on how the previous round played out. Light showers will hang around through the morning, feeding off remnant outflow boundaries. Friday afternoon upper ridging to the west and high pressure at the surface begin to push into the region. This forces the surface low and quasi- stationary boundary to jump southeast. Timing of this jump will have a large impact on when and where storm formation will take place. Current guidance indicates storms are more likely to form over northwest Iowa, just southeast of the CWA border. However, there are large differences in guidance, and therefore certainty in timing is low. Once storms do form, they will have the potential to be strong to severe as outlined by the SPC Day 3 Slight Risk (level 2 of 5).

Saturday we finally get a break from storms with a dry forecast. Highs look to climb into the 80s and 90s with slightly breezy southeast winds. During the day Sunday also looks to be dry with another day of 80s and 90s and breezy southeast winds. Storm chances return late Sunday night and continue into the first portion of next week. However, model divergence increases greatly, keeping confidence low.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 608 AM CDT Thu Jun 4 2026

Overall most of the area will see VFR conditions throughout the day. Spotty showers will be possible in mainly northwest IA this morning with a very isolated thunderstorm possible. The better chance for thunderstorms will be very late this afternoon into the evening near highway 14, especially on the SD side. A few of these storms could be strong to severe. If these storms develop they may begin to drift southeast overnight, but will likely weaken.

FSD WATCHES/WARNINGS/ADVISORIES

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