textproduct: Sioux Falls

KEY MESSAGES

- Elevated to critical fire danger is expected today. A Red Flag Warning has been issued for many areas along and west of I-29 where confidence is highest in critical fire danger conditions being met. The Warning is in effect from noon to 7pm today.

- Spotty light showers are possible southeast of IA/MN Highway 60 through daybreak. Potential for additional showers or stronger storms in northwest Iowa today has decreased.

- Monday brings the best chances (30-60%) for strong to severe storms. However, there remain uncertainty regarding the location in where storms develop. Continue to check the forecast for the latest updates.

- Chances (30-50%) for showers and storms look to persist through the rest of the week. Details remain uncertain at this time.

UPDATE

Issued at 345 AM CDT Sun Apr 12 2026

A couple of changes for today. First, latest SPC outlook for today has removed the Marginal (Level 1 of 5) from the eastern portions of our forecast area today. This aligns with our thinking as we should be more prevalent subsidence in the wake of a subtle wave sliding through this morning, which should preclude additional storm development this afternoon.

As a result, our primary concern for today remains elevated to critical fire weather and the coverage of a Red Flag Warning. Models continue to support a deep unidirectional southwest to west flow by midday, with significant drying expected to mix to the surface, especially in the southwest quadrant of our forecast area (along/south of I-90 and along/west of I-29). This scenario is often handled well by the HRRR/RAP during this time of year, so have blended some of these solutions into our winds and dew points (relative humidity) for this afternoon. This increased confidence in seeing several hours of Red Flag conditions as far east as I-29 but generally south of SD Hwy 34, so have expanded the Red Flag Warning as far east as Minnehaha/Lincoln/Union counties in SD and Dixon County Nebraska. May still need further expansion into portions of southwest MN and far northwest IA, but confidence is lower that the timing of critical humidity levels and winds in these areas would sufficiently overlap, so will let the day shift continue to assess and expand if needed.

DISCUSSION

Issued at 300 PM CDT Sat Apr 11 2026

Warm advective rain showers have pushed off to the east this afternoon. However, moist low levels has kept low level stratus around. This has kept high temperatures in the mid 40s to mid 60s, warmest across south central South Dakota. This is due to winds taking on a south/southwest component across south central South Dakota, resulting in clearing the stratus across this area. Breezy winds will be persistent though and last through the overnight hours. With breezy winds and stratus in place, only have low temperatures falling to the 50s across the area. There remains the possibility of a rouge storm or two late tonight. Should a storm develop, it would be across parts of northwest Iowa. This seems unlikely (15% chance) as of now as warm air advection (WAA) strengthen aloft without advecting sufficient moisture with it. This will lead to an increasing cap above the moist stable later. If a storm can form, then it would have the potential to be strong to severe given sufficient

Low level winds will turn westerly for the day tomorrow and remain breezy. High temperatures look to significantly warm into the upper 70s and and low 80s across the area. With drier westerly flow in place, humidity levels will drop, resulting in critical fire danger being reached. More details can be found in the fire weather discussion below. The westerly winds will advect drier air into the area throughout the day. However, guidance is persistent in showing this drier air shoving the better low level moisture all the way down to portions of northwest Iowa. This moisture boundary would be the location for a rouge storm to develop on. However, a weak shortwave trough will already be east of the area, promoting subsidence on its backside. Thus, Sunday looks to be mostly dry though there remains the outside chance (15-30%) that a few showers or storms develop along and southeast of this boundary. Any fire danger will come to an end during the evening hours as the boundary layer stabilizes. WAA will restrengthen aloft ahead of an incoming exit region of an upper level jet tied to a shortwave trough. Moisture looks scarce above 900mb and with the WAA strengthening the low level inversion. Again, the potential for any showers remains low at 15% or less through the night. If a storm is able to form, it could be strong to severe. Low temperatures will fall to the 40s and 50s overnight.

Monday looks to have the highest chances for strong to severe storms as medium range guidance is in decent agreement in a shortwave trough pushing through the Northern Plains. The mass response to this wave will result in southerly return flow and moisten dew points across the forecast area. With mid level lapse rates to above 8C/KM aloft. This will result in the potential for large buoyancy. There remains some uncertainty though as some of the guidance shows the bulk of the moisture getting advected to the east of the area. This possibility would happen if the surface low races east of the area and and introduces westerly surface winds on its back side. If the incoming shortwave is slower aloft, then the surface low will not quickly race off to the east and thus leave a broader warm sector across the area. The other component to potential severe weather is the cap. Latest guidance continues to support a strong cap above the warm sector. At this time, the longer range CAMs such as the RRFS, NAM3km, and FV3 do show convection firing along the warm front. But, this front is just north of the area. With the mean wind remaining out of the southwest, these storms would quickly push off to the northeast. Latest REFS also suggests this solution as well as convergence is strongest along the warm front north of the forecast area. As of now, only the deterministic Euro, Euro ensemble, and AIFS (AI Euro) show the warm front remaining draped across I-90 and thus producing convection Monday afternoon. Think the current SPC Day 3 outlook remains valid given this remaining uncertainty.

The warm sector looks get shoved further south and east of the forecast area on Tuesday. While the main wave will eject out of the Rockies on this day, keeping severe storm chances around. If the boundary remains off to the south and east, then storms chances would be lower. If the boundary remains across the forecast area, then storm chances would increase across the area. Tough to say which solution is correct at this time but something to keep an eye on over the next few days. The upper level pattern diverges towards the middle and end of next week but additional chances for showers and storms remain possible. Aside from rain chances, high temperatures look to remain above average in the 70s and 80s through Friday.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1241 AM CDT Sun Apr 12 2026

A mix of VFR down to IFR across the region this evening due to layer of lingering low stratus east of I-29. Clouds are expected to lift and thin through the overnight hours, gradually raising to VFR. At the same time high level cirrus is flowing into the region from the south. A few light sprinkles are possible southeast of Highway 60, but are not expected to impact TAF sites. Cirrus clouds flow off to the east through the morning, becoming mostly clear by afternoon.

Breezy southerly winds gusting 20-30 kts will begin to to the west over the next few hours. Gusts of 20-30 kts will continue through the late afternoon. Highest at areas of elevation over south central South Dakota, and the Buffalo Ridge area of southwest Minnesota. Winds rapidly decrease in the early evening becoming light and variable through the end of the period.

FIRE WEATHER

Issued at 345 AM CDT Sun Apr 12 2026

Today will start off rather humid with areas of gusty winds along and east of U.S. Highway 81 in response to strong south-southwest flow above the surface. As the day progresses, a weak boundary will slide east across southeast South Dakota into northwest Iowa, turning surface winds more to the southwest and west. By midday, deeper mixing will pull much drier air to the surface in areas west of this boundary as temperatures climb into the 70s to lower 80s. As a result, relative humidity levels along and south of the I-90 corridor and at least as far east as I-29 will fall below critical levels, reaching 17 to 22 percent in the mid to late afternoon. Deeper mixing will also support occasional stronger wind gusts, reaching 30 to 35 mph at times in these areas. These conditions are expected to last for several hours, supporting expansion of the Red Flag Warning east to include a portion of I-29 (Minnehaha to Union County South Dakota) as well as Dixon County Nebraska.

There is some potential that critical conditions may overlap for more than an hour or two in some areas east of I-29. However, confidence is currently not high enough to expand the Red Flag Warning into areas east of I-29. Trends will be monitored throughout the day, and further expansion of the warning is possible.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from noon today to 7 PM CDT this evening for SDZ050-052-053-057>071. MN...None. IA...None. NE...Red Flag Warning from noon today to 7 PM CDT this evening for NEZ013.