textproduct: Sioux Falls

KEY MESSAGES

- An isolated strong to severe storm remains possible through 6 pm for portions of northwest Iowa. Quarter sized hail is the main threat.

- Unseasonably warm temperatures, very low humidity, and breezy southwest wind gusts lead to a critical fire danger Thursday. A Red Flag Warning has been issued for south central and southeast South Dakota and far northeast Nebraska. Additional fire concerns possible Friday but confidence is low.

- A strong cold front moves through the area on Friday. Ahead of the front over parts of northwest Iowa and southwest Minnesota, an isolated severe storm is possible. Behind the front, much cooler air moves in and any rain may briefly change to a wintry mix and/or snow near and north of Highway 14 as precipitation exits the area.

DISCUSSION

Issued at 220 PM CDT Wed Apr 15 2026

Strong to severe thunderstorms have stayed south and west of the area thus far today. Instability has been marginally supportive of at least some occasional rumbles of thunder today, and as we reach the peak of daytime heating, a few more hundred J/kg of CAPE will develop. This may lead to slightly better coverage of thunderstorms mainly south of a Sioux Rapids to Sioux City, IA line, but the chances for severe weather look quite low. There's still around 45-55 kts of bulk shear, so if a decent updraft can get going and sustain itself, then quarter sized hail cannot be ruled out. This threat ends around 6 pm as storms move off to the east. Quiet weather expected tonight as the main upper wave responsible for the rain moves off to our east. Lows tonight drop to the middle 40s for the most part across the area by Thursday morning.

Winds start turning more southwesterly heading into the day on Thursday, which will help usher in warmer and drier air into the area and leading to critical fire weather conditions. More on this in the fire weather discussion below. For Thursday night into the day on Friday, a deep trough extending from the northern Rockies into the Four Corners will move through the area. At the surface, a strong cold front will sweep across the area during the day on Friday. By 1 pm on Friday, deterministic and ensemble guidance has the front either just east of the IA/MN Highway 60 corridor or just east of the forecast area. These faster solutions will limit the potential for severe weather in our area as the better instability would develop off to our east. So still a low confidence severe weather forecast, but a very isolated strong to severe storm still remains possible over parts of northwest Iowa and southwest Minnesota early Friday afternoon if the cold front slows down or a storm is able to develop just before the front clears the area.

Colder air will be rushing in behind the front as guidance is in good agreement of a strong push of cold air advection (CAA) following the frontal passage on Friday. This means for most of the area, the morning will be warmer than the afternoon, so dress accordingly! With the colder air moving in, any precipitation leftover behind the frontal passage could turn to a wintry mix or snow as the system exits the area. Latest guidance is trending towards our area drying out before the coldest air arrives, limiting the chance for wintry weather. There is a potential where at least some rain could turn to wintry precipitation along portions of the Highway 14 corridor Friday morning/early afternoon, but this would likely be short-lived and thus cause little impacts. Still time for things to change, so be sure to keep up to date with the latest forecast! This push of CAA will also lead to windy conditions Friday into Saturday, with northwesterly gusts to 30 to 40 mph expected both days, strongest on Friday. Temperature-wise, look for lows down into the 20s to lower 30s Saturday morning and then the 20s area- wide by Sunday morning. Highs on Saturday will struggle to make it to the 50s for the most part, coolest east of the Missouri River. Ridging aloft looks to build into the area heading into early next week, which will help bring about a warming trend with limited rain chances through the start of the next work week.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1241 PM CDT Wed Apr 15 2026

Additional showers and thundershowers will be lifting through the Highway 20 corridor over the next few hours, but the better chance of strong to severe storms look to remain just south of the area. Still lower confidence on the potential for a storm at KSUX given the sporadic nature of any development, but still enough confidence to keep the PROB30 group in there for -TSRA, but adjusted the times slightly. Otherwise, VFR conditions are expected through the TAF period as any fog tonight should stay east of our area. Winds will be mainly light and variable this afternoon into tonight, but winds will be increasing into the day on Thursday. By the late morning/early afternoon on Tuesday, look for southerly gusts upwards of 20-25 kts.

FIRE WEATHER

Issued at 220 PM CDT Wed Apr 15 2026

Winds remain light across the area this afternoon, so fire weather concerns are not expected into this evening. South- southwesterly winds will increase on Thursday as a storm system deepens off to our west. Relative humidity values look to drop as low as 15-20% across the area in the afternoon as temperatures warm into the lower to middle 80s. This dry air will combine with gusts of 25-30 mph to lead to critical fire weather conditions across a large part of the area. For this reason, upgraded the Fire Weather Watch for south central and southeastern South Dakota and far northeastern Nebraska to a Red Flag Warning.

A little uncertainty remains on how far east the strongest winds make it, but enough confidence to issue a Fire Weather Watch for parts of southwest Minnesota into adjacent areas of northwest Iowa where RH values will drop to around 20-25%. Farther south to the Highway 20 corridor in northwest Iowa, went with a Fire Weather Watch instead of a Red Flag Warning due to uncertainty regarding how much rain we see down there today. If we could get more of a steady rain develop and/or a couple of thunderstorms move through this afternoon, that may preclude a greater fire danger despite the low RH and breezy winds expected.

Winds remain elevated and even increase on Friday as a cold front moves through the area and turns winds from the south to out of the northwest. Drier air will filter in behind this front, dropping RH values by Friday afternoon. This will lead to a primarily wind driven high to very high GFDI across the area; however colder temperatures moving in and cloud cover precludes a greater fire weather threat at this time.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from noon to 8 PM CDT Thursday for SDZ038>040- 050-052>071. MN...Fire Weather Watch from Thursday afternoon through Thursday evening for MNZ071-072-080-089-097-098. IA...Fire Weather Watch from Thursday afternoon through Thursday evening for IAZ001-012-020-031. NE...Red Flag Warning from noon to 8 PM CDT Thursday for NEZ013-014.