textproduct: Sioux Falls

KEY MESSAGES

- Isolated strong to severe thunderstorms are possible especially west of I-29 tonight. Large hail up to golf ball in size and 70 mph will be the main threat. Storms look to generally weaken with eastward extent.

- A Heat Advisory has been issued for some areas Sunday into Monday, and further adjustments to headlines are possible in the coming days.

- Summer heat and humidity is expected Sunday into next week. Daily heat indices of 95 to 105 degrees will lead to Major to locally Extreme Heat Risk at times. Begin planning now to reduce the risk of heat illness and impacts.

- An active pattern through the week leads to periodic moderate chances for showers and storms. Uncertainty in the timing of rain also brings lower confidence in daytime high temperatures.

UPDATE

Issued at 956 PM CDT Sat Jun 27 2026

A broken line of strong thunderstorms extends across most of western South Dakota and into the northern Nebraska panhandle this evening. These will be the storms to watch as they gradually lift northeastward through the night aided by a strengthening low level jet. Latest soundings still show a strong capping inversion in place over our area through the night, but the cap will be the weakest along the US Highway 14 corridor in eastern South Dakota especially closer to the James River Valley late this evening. So this area looks to have the better chances of wind gusts of 60-65 mph, but this threat still appears to be isolated due to the overall strong cap.

Farther south along this line over northern Nebraska is a cluster of thunderstorms with embedded supercell structures that is capable of quarter to golf ball sized hail. These storms will be watched closely as well as they lift towards south- central South Dakota later around midnight as this will be in an area of higher instability. However, the same capping issues remain and so this threat for large hail will also remain isolated. Instability and shear will gradually lessen with eastward and especially northeastward extent, and thus the storms will continue weakening as they push eastward heading into early Sunday morning. However, storms will still be capable of small hail and wind gusts to 40 mph by the time they reach the I-29 corridor and points east.

There is an alternate, but less likely scenario where the storms are able to maintain their strength as they push across the area through the night and bring 60-65 mph winds and large hail to a wider swath of the area. Given the strong cap already discussed, this scenario is unlikely, but if storms can take full advantage of a potential 40-50 mph LLJ, this can't be entirely ruled out. The greater threat for severe weather in this alternate scenario would be near and south of I-90 where there will be greater instability and the strongest LLJ.

Timing-wise, look for the storms to start moving into the area around midnight and reach the I-29 corridor by 3-5 am and then exiting the area off to our east by 7-9 am. One other thing to note is that though the storms will be quick-moving, some guidance indicates a narrow, but long swath of a quick 2-4" of rain with these storms which could result in some minor urban flooding.

DISCUSSION

Issued at 1248 PM CDT Sat Jun 27 2026

The first concern will be the potential for thunderstorms tonight. The current run of models is really pushing for a strong capping inversion, which strengthens through the night. This suggests that tapping into the deeper instability may be impossi.ble. Above this capping inversion some moisture and weak (500 J/kg) instability may allow for some ACCAS showers and thunderstorms late tonight into Sunday morning, but any severe threat would be very limited. Will need to see some fairly large changes in the upcoming data and model runs for the severe threat to become more prevalent. If a storm can tap into the lower, deeper instability (2500-3000 J/kg) a very isolated threat for hail to the size of golf balls is possible.

Very warm air and a continued strengthening capping inversion barrels north on Sunday, which should shut down convective chances through about Monday night. Later Sunday night into Monday morning some patchy elevated showers or storms will be possible but for now confidence is too low and will keep chances at 20 percent or less.

Concerns for heat ramp up Sunday but one big question mark remains, stratus. The latest run of the nam has some fairly deep and widespread stratus that would really bite into the afternoon heat indices. For now confidence is not high enough to drop the heat advisory but will need to monitor the trends of this stratus as well as the trends of the dew points. The nearest 70+ dew point in south central NE and surface winds are expected to remain southeast into Sunday morning.

Monday may prove to be the hotter more humid day with less chance for stratus. Expanded the heat advisory into parts of southwest MN to cover the potential for more widespread heat indices above 100. Monday does look to be windy which will help take the edge off of the heat a touch.

Otherwise, Tuesday through Saturday will have southwest flow aloft with the stronger upper level ridging just to the east of the area. This will allow periodic waves to move through the area with off and on threats for showers and thunderstorms. More than likely this upper level pattern will keep the extreme heat at bay most of the days, but still see highs from the upper 80s to mid 90s. But with these threats for showers and thunderstorms will come "unexpected" outflow boundaries and stratus at times so there will be some variability in which days are hottest and which are less hot.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1249 AM CDT Sun Jun 28 2026

A broken line of showers and thunderstorms is moving into eastern South Dakota to start the period. There have been a few gusts in excess of 50 kts at times along the line, and this will continue to be the main threat over the first couple hours of the period. Storms look to gradually weaken with eastward extent, but there is still some uncertainty as to how far east these storms will get before they become consistently sub-severe. With all that said, the greatest threat of 50+ kt wind gusts will be west of I-29.

MVFR to locally IFR stratus will impact the area in the wake of these storms, with this stratus deck gradually eroding and lifting from south to north through the morning and early afternoon hours. After this stratus deck erodes, VFR conditions can be expected for the rest of the afternoon through the end of the period.

Breezy southeasterly winds will continue through the morning hours, gradually diminishing from west to east heading towards the afternoon hours today. Winds will turn light this evening across the area except over portions of northwest Iowa where southeasterly winds will be sustained around 10 kts through the end of the period.

CLIMATE

Issued at 410 AM CDT Sat Jun 27 2026

Summer heat builds into the area from Sunday through much of next week. This will lead to a potential for a few temperature records to be tied, or possibly broken:

Current Record Highs:

Monday (06/29): KFSD(101|2002) KSUX(100|2022)

Current Record Warm Lows:

Monday (06/29): KFSD(77|2020) KSUX(80|1931) KHON(75|2020)

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory from 1 PM this afternoon to 9 PM CDT Monday for SDZ062-066-067-069>071. Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for SDZ060-061-065-068. MN...Heat Advisory from 1 PM to 9 PM CDT Monday for MNZ072-080-081- 089-090-098. IA...Heat Advisory from 1 PM this afternoon to 9 PM CDT Monday for IAZ001>003-012>014-020>022-031-032. NE...Heat Advisory from 1 PM this afternoon to 9 PM CDT Monday for NEZ013-014.