textproduct: Sioux Falls

KEY MESSAGES

- Isolated showers/sprinkles continue through the early morning hours. A few rumbles of thunder are possible; severe weather is not expected.

- Critical fire danger expected today with northwest winds gusting 35-40 mph and relative humidity values at or below 25%. Red Flag Warning is in effect from Noon until 9 pm CDT.

- Elevated to near critical fire weather concerns again Thursday as wind gusts increase to 35-45 mph.

- Warmer conditions are expected this week with highs 10 to 20 degrees above normal. Friday and Saturday warm into the mid 80s to lower 90s.

UPDATE

Issued at 310 AM CDT Tue May 12 2026

A fast moving wave to the northeast will swing weak lift and instability through the area early this morning. This will result in spotty showers and very isolated rumbles of thunder. By about 15z this activity should be out of the area, although some weak lift does linger from about Sioux City towards Ida Grove through about 18z.

Behind this wave strong mixing is expected with temperatures climbing into the 70s. With afternoon relative humidity expected to drop as low as about 18-25 percent along with wind gusts of 30 to 40 mph, critical fire weather conditions are expected. The most susceptible locations will be warm season grasses that are just beginning to green up. However, even the shorter cool season grasses that have greened up are already beginning to show signs of stress with little precipitation since the widespread rain event 2 weeks ago. Extreme care should be taken with outdoor activities that involve fires or could spark a fire.

Otherwise the next day of concern for fire weather will be Thursday when southerly winds may gust to 35 to 45 mph. What could offset this will be some mid level moisture and lift ahead of an incoming wave that will likely bring an increase in cloud cover as well as scattered showers and isolated thunderstorms. While very rare in this area, there is at least a small chance for some dry lightning given the dry low levels on Thursday. Something to keep an eye on.

DISCUSSION

Issued at 336 PM CDT Mon May 11 2026

Despite the recent green up, lack of beneficial rain in the past ten days or so has resulted in some of the growth beginning to dry out. Combine this with highs in the 70s to 80s (increasing from east to west), relative humidity falling to 30% or less, and southerly winds gusting 20-30 mph will result in elevated fire concerns for this afternoon. Please use caution with sources of sparks and report any fires immediately. Lows for tonight will be warm, in the 50s to 60s.

This evening and overnight the strongest winds will shift east of I- 29 ahead of an approaching cold front. As it does so there will be a very brief lull in winds as they turn to the northwest. Along with the frontal passage is a low chance (<20%) of light rain. However, a very dry airmass will be present over the region. Limiting what makes it to the ground to just very light sprinkles if anything. Winds will increase through the morning, reaching their peak in the early afternoon at 35-40 mph. With soundings indicating steep low level lapse rates, deep mixing tapping into a 35-40 kt LLJ, and northwest winds aloft well aligned, there is potential for winds to overperform. After discussion with neighbors, have blended in a little RAP13 and HRRR into the NBM to boost peak winds and gusts. This results in sustained winds very near to Wind Advisory criteria, while gusts remain shy of criteria by 2 or 3 kts. Collaboration with neighbors came to the conclusion to hold off on wind headlines at this time, but will monitor the trends with the upcoming model runs.

Highs will be slightly cooler thanks to CAA behind the front, in the low to upper 70s. However, the previously mentioned dry air over the region will work to decrease the relative humidity values to less than 25% for most of the region. The combination of strong winds and low humidity will result in High Grassland Fire Danger for Tuesday. As such, have issued a Red Flag Warning for southeastern South Dakota, northeastern Nebraska, southwestern Minnesota, and northwestern Iowa on Tuesday from Noon until 9 pm CDT. More on this in the Fire Weather Discussion below.

Wednesday the dry air mass remains in place as an upper ridge and surface high pressure move over the region. Highs will climb into the mid to upper 70s with some 80s possible along the southern Missouri River Valley. Relative humidity values will once again fall to less than 25% for most of the region, however winds will be light and variable. At this time there is no plan for a fire headline. Despite that, please continue to use caution so as not to spark a fire. Thursday relative humidity values recover slightly, but remain less than 30% for the entire region, with central South Dakota seeing values of 25% or less. Winds will be strong out of the south, with sustained winds 25-30 mph and gusts 35-40 mph. A few isolated gusts of 45+ mph are also possible. These conditions will lead to the Grassland Fire Danger to increase to High to Very High. Please keep an eye on the forecast for Thursday, as fire and wind headlines may be necessary.

In addition Thursday night into Friday morning an upper trough will pass north of the region. As it does so it will drag a cold front through that may work to trigger some showers and thunderstorms. Uncertainty in strength and areal coverage remains high as models begin to diverge. Additional chances for showers and thunderstorms continue into the weekend.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 614 AM CDT Tue May 12 2026

Scattered sprinkles and very light showers will continue through mid to late morning, drifting southeastward. Otherwise, VFR conditions are expected. The main concern will be northwest winds gusting to 30 to 40 mph late this morning into the evening.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from noon today to 9 PM CDT this evening for SDZ038>040-050-052>071. MN...Red Flag Warning from noon today to 9 PM CDT this evening for MNZ071-072-080-081-089-090-097-098. IA...Red Flag Warning from noon today to 9 PM CDT this evening for IAZ001>003-012>014-020>022-031-032. NE...Red Flag Warning from noon today to 9 PM CDT this evening for NEZ013-014.