textproduct: Sioux Falls

KEY MESSAGES

- Dangerously hot conditions are expected mainly south of I-90 this afternoon, with heat index values climbing to at or above 100F. The hottest conditions will be along and just north of Highway 20 where the heat index will peak around 106-108F, though locally hotter spots can't be ruled out.

- Severe weather appears unlikely tonight, with the better chances north and east of the area. A few non-severe storms still may clip portions of southwest Minnesota by daybreak.

- Chances for strong to severe storms return to the area Monday afternoon and evening mainly near and south of Highway-20. Large hail up to the size of golf balls and damaging winds to 70 mph are the main hazards.

UPDATE

Issued at 947 PM CDT Sun Jul 19 2026

Gusty thunderstorms over south-central South Dakota have weakened likely due to its anvil spreading east of the storms and allowing some stabilization in the otherwise hot and humid airmass. Additional development ahead of this is unlikely as CIN increases over the next couple of hours.

An upper level wave will be diving southeast across southern Canada and into the Great Lakes region tonight into tomorrow, which will drag a cold front across the northern Plains and upper Midwest through the day on Monday. Storms tonight will likely be forming closer to this upper level support, mainly over northern Minnesota down to adjacent areas of eastern North Dakota and northeast South Dakota, and thus the local storm threat still remains low for the overnight hours. Heading into the daytime Monday, heating ahead of the front will lead SBCAPE values quickly exceeding 2,000 J/kg over southwest Minnesota and adjacent areas of eastern South Dakota by mid-morning, and as such, some guidance shows some storms developing along the front as early as Monday morning to early afternoon. Despite the front providing some good lift, the CAP still looks to be strong enough to prevent this from happening, so this scenario seems unlikely at this time. Rising parcels will likely have a better chance of breaking a weakening CAP down along Highway 20 by the mid to late afternoon hours as the cold front moves into the area. Timing differences amongst the models with this front still lend itself to a low confidence forecast, but any storms that do form there will be capable of gusts to 70 mph and hail to the size of golf balls so make sure to stay weather aware.

Lastly, heat will build ahead of this front, allowing for heat index values to exceed 100 degrees mainly south of I-90 and so the Heat Advisory remains in good shape. Stay hydrated out there!

DISCUSSION

Issued at 229 PM CDT Sun Jul 19 2026

A few light showers persist across the area this afternoon. These showers are also accompanied by a mid level cloud deck which has kept temperatures a bit cooler than previously expected. However, sunshine remains across parts of south central South Dakota. Thus, temperatures have warmed to the upper 70s, 80s, and a few locations pushing into the 90s. With dew points remaining in the 60s to low 70s, heat indices have warmed to the 80s and 90s with a few locations hitting 100F. With some diurnal warming left to go, should still see the heat indices nudge a little higher, allowing for the Heat Advisory to remain in effect until 9PM this evening. Another round of showers and thunderstorms remains possible late tonight into tomorrow morning (11PM to 6AM). These storms will develop along a cold front in North Dakota and move southeastwards through the evening hours. These storms may grow into a line as they push southeastwards. However, there remains some uncertainty in whether these storms will push into southwest Minnesota or stay just outside the forecast area. These storms look to be focused on the nose of the low level jet where convergence and the strongest warm air advection (WAA) will lie. The bulk of the hi-res guidance and the ensembles also support the storms remaining in this location. Still have left light chance to chance PoPs across southwest Minnesota in case lingering showers and storms pass through the area.

The thermal ridge will push directly over the forecast area on Monday, pushing 850 mb temperatures up to +25C to about +30C. Mixing these temperatures down to the surface will result in widespread high temperatures up to the 90s to low 100s, hottest along the Missouri River Valley. With dew points remaining in the 60s to low 70s, heat indices will warm up to 100F to 105F south of I-90. As such, have issued another Heat Advisory for this area. The Advisory is in effect from noon to 8 pm. The previously mentioned cold front will be pushing through the area throughout the day. While this front will cool temperatures, the main cold advective push from the front will come in the late afternoon and evening timeframe, thus allowing for hot and humid conditions to continue. This front will serve as the focal point for additional showers and storms between 4PM and 10PM. The front will push through rather quickly, limiting the severe weather threat to near and south of highway-20. Storms look to remain more discrete as the develop and quickly race out of the area along the boundary. The moisture pooling along the boundary will push CAPE values up to 2,000 to 2,500 J/kg. Hodographs show deep layer shear values on the order of about 45 knots. Hodographs are generally straight with slight backing aloft. This should allow for large hail up to the size of golf balls. DCAPE will also be high around 1,500 J/kg, resulting in the potential for damaging winds to 70 mph. Since these storms are discrete and look to only impact a small area, should only see isolated impacts from severe storms. Once the front pushes through, temperatures will fall to the 60s to low 70s overnight.

Tuesday will be a cooler day with the post frontal airmass in place. High temperatures will be seasonable in the 80s with dew points falling to the 50s. While this would usually make for a pleasant Summer day, smoke will filter in behind the front which could affect sensitive individuals. Fortunately, it looks like the highest concentration of smoke will come Monday night into Tuesday morning and be slowly decreased thereafter. These seasonable conditions will persist for the rest of the work week as northwest flow persists aloft. Next chances for rain look to come on Thursday and Friday as a shortwave trough pushes through the area. The ensembles support this as they show a 40-60% chance for rainfall amounts exceeding a tenth of an inch for this period of time. Instability looks to be quite limited, so severe storms are not expected at this time. Upper level ridging looks to potentially make a comeback next weekend, leading to a return of above average temperatures. This potential remains uncertain so will keep an eye on how the pattern evolves over the next week.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1257 AM CDT Mon Jul 20 2026

A few showers and thunderstorms may clip portions of southwest Minnesota through the early morning hours today. A better, but still uncertain, chance of storms will occur late this afternoon into the early evening mainly near and south of Highway 20. Latest guidance continues to bring most of this activity south of our area, but can't rule out a storm in and around KSUX with this round. However, left out mention in the TAF as chances of impacts there remain low, only around a 10-25% chance.

Winds will turn from the south to out of the west and then the northwest through the day today as cold front moves across the area from north to south. Winds may gust up to 20 kts mainly along the Highway 14 corridor this afternoon behind the front before tapering off through the evening. Lastly, LLWS remains a concern mainly near and north of I-90 through the early morning hours due to a strengthening low level jet. Can't rule out winds locally up to 50 kts up around 2,000 ft in spots north of I-90 through sunrise.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory from noon today to 8 PM CDT this evening for SDZ050-063>069. Extreme Heat Warning from noon today to 8 PM CDT this evening for SDZ070-071. MN...None. IA...Heat Advisory from noon today to 8 PM CDT this evening for IAZ001>003-012>014. Extreme Heat Warning from noon today to 8 PM CDT this evening for IAZ020>022-031-032. NE...Extreme Heat Warning from noon today to 8 PM CDT this evening for NEZ013-014.