textproduct: Sioux Falls

KEY MESSAGES

- Strong southerly winds and critical relative humidity values will lead to dangerous fire weather concerns today. As a result, a Red Flag Warning is in effect for most areas from 12pm-8pm. Avoid any outdoor burning as a fire could quickly spread out of control!

- Scattered thunderstorms will move across the region Wednesday night through Thursday with the passage of a strong cold front. Some storms may become strong to severe, capable of producing large hail and damaging winds. There is a Level 2 of 5 risk for severe thunderstorms Thursday afternoon and evening for areas along and east of Highway-60.

- A return to more seasonable temperatures is expected by the weekend with highs in the mid 50s to lower 60s. While not a wash out, there are also low to moderate chances (30%-60%) chances for showers and thunderstorms during this period.

UPDATE

Issued at 415 AM CDT Wed Apr 22 2026

Taking a look across the area, mostly clear conditions continue this morning as temperatures fall into the low to mid 50 for most areas. Besides the mild start to the day, confidence is growing in a few "popcorn" showers developing across northwestern IA as a strengthening 850 mb LLJ interacts with about 300-500 J/kg of instability ahead of a weak wave. While we're not expecting anything severe, could see a few pockets of moderate rain develop with an occasional rumble of thunder if things can get going. Shifting gears here, the forecast remains on track for dangerous fire concerns this afternoon/evening as increasing southerly winds (35-45 mph) and low relative humidity values (15%-30%) leads to very high to extreme fire danger for most areas (more details in fire weather section). Otherwise, summer-like conditions are expected today as highs peak in the 80s and 90s with the warmest conditions west of I-29. With this in mind, make sure to stay hydrated and take frequent breaks if working outdoors! Lastly, an advancing cold front will bring low to moderate chances for scattered showers and isolated thunderstorms to areas along and west of I-29 overnight.

DISCUSSION

Issued at 148 PM CDT Tue Apr 21 2026

Wednesday will be hot, dry, and windy as a strong 500 hPa ridge moves overhead. The 12Z HREF Grand Ensemble is showing a 60+ percent chance of high temperatures greater than 85 degrees across most of SD and parts of southwest MN with similar probabilities of 90 degrees or higher along and west of the James River Valley. Some locations could approach record values for the day. Afternoon southerly wind gusts will reach 40 to 45 mph given deep boundary layer mixing. This heat and wind, combined with very dry fuels and low humidity will result in critical fire weather conditions. See Fire Weather discussion for additional details concerning the newly issued Red Flag Warning.

Attention then shifts to a large closed 500 hPa low centered over the Northern Rockies Wednesday night through Thursday. A strong leading short-wave is progged to lift northeastward across the Northern Plains during this time. Forcing aloft, combined with an eastward advancing surface cold front/dry line will provide the focus for thunderstorm initiation. Ahead of the surface boundary, dewpoints will rise into the upper 50s and lower 60s, resulting in MUCAPE up to 1500 J/kg.

Some thunderstorm activity is possible Wednesday night west of I-29 with the approaching boundary, but the severe threat is lower. Main concern is for areas along and east of I-29 Thursday afternoon/evening. While this area is highlighted by a SPC Day 3 Level 2 of 5 severe weather risk, much will depend on the longevity of a strong 700 hPa thermal cap, widespread low cloud cover ahead of the front, and the timing of the front itself. Right now, the best chances for severe storms exist across southwest MN and northwest IA from 4pm into the early evening. The primary hazards would be hail to the size of quarters and damaging wind gusts to 60 mph.

Passage of the cold front Thursday night will usher in a more seasonable airmass Friday into the weekend with highs from the mid 50s to lower 60s. Aforementioned 500 hPa low continues to wobble across southern Canada into early next week, allowing other short-waves to traverse the Northern Plains. Predictability in the strength and timing of these waves is low, so NBM chance POPs seem reasonable at this time.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 632 AM CDT Wed Apr 22 2026

Mainly VFR conditions will continue this TAF period. Taking a look at satellite imagery, a few scattered showers and thunderstorms have developed across the lower Missouri River Valley this morning promoting some occasional MVFR cigs with moderate rain. While this developing area won't hang around long, should see things continue to move out of our area by mid morning. Otherwise, mostly clear conditions are expected for the rest of the day. Southeasterly winds will become more southerly and increase with gusts between 35-45 mph expected through this evening. Lastly, could see a few additional scattered showers develop overnight as another MVFR cloud shield develops.

FIRE WEATHER

Issued at 415 AM CDT Wed Apr 22 2026

We're still on track for a dangerous fire weather set up today. Starting this morning, a tightening SPG will gradually increase southeasterly winds speeds as mixing resumes. By early afternoon, mixing will deepening helping warmer and drier air make its way to surface. This will lead to warmer temperatures and drier dew point resulting in critical relative humidity values in the 15- 30 percent range with the driest conditions west of the James River Valley. Strong southerly winds will also develop by late afternoon with gusts between 35-45 mph expected. As this becomes collocated with the driest RH values, the conditions will become favorable for rapid fire spread especially west of I-29. As a result, a Red Flag Warning remains in effect from 12pm to 8pm for most areas. Lastly, with the breezier conditions expected to persist overnight; could see the fire concerns hang around for a bit longer this evening as RH values are slow to recover west of the James River Valley.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from noon today to 8 PM CDT this evening for SDZ038>040-050-052>071. MN...Red Flag Warning from noon today to 8 PM CDT this evening for MNZ071-072-080-081-089-090-097-098. IA...Red Flag Warning from noon today to 8 PM CDT this evening for IAZ001-002-012. NE...Red Flag Warning from noon today to 8 PM CDT this evening for NEZ013-014.