textproduct: Sioux Falls

KEY MESSAGES

- Tuesday will see critical fire danger with northwest winds gusting 35-40 mph and relative humidity values decreasing to less than 25% for most of the region. A Red Flag Warning is in effect from Noon until 9 pm CDT.

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

- Warmer conditions are expected this week with highs 10 to 20 degrees above normal. Thursday and Friday should see highs in the mid 80s to lower 90s.

- Dry weather remains for most of the week. Starting to see increased chances for showers and thunderstorms late week into the weekend.

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 /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1255 PM CDT Mon May 11 2026

VFR conditions are expected for the period. High level scattered to broken clouds will prevail. Southerly winds will be gusting 20-30 mph. Strongest gusts located west of I-29 for this afternoon. This evening the strongest gusts will shift to the east of I-29. A very brief lull in winds as a cold front moves through the region from northwest to southeast near or shortly after midnight tonight. Winds will become northwest with gusts through the morning, peaking at 35- 40 mph. A period of LLWS is expected with the passage of the front.

FIRE WEATHER

Issued at 336 PM CDT Mon May 11 2026

A Red Flag Warning is in effect from Tuesday at Noon until 9 pm CDT for southeastern South Dakota, northeastern Nebraska, southwestern Minnesota, and northwestern Iowa. A very dry air mass settles over the region behind an early morning cold front. Relative humidity values are expected to fall to less than 25% with most of the region seeing values as low as 19-22%. In addition, northwesterly winds will increase behind the front. Sustained winds of 20-30 mph will be widespread along with gusts of 35-40 mph. The combination of strong winds, very low relative humidity, and warm highs in the 70s is what prompted the Red Flag warning.

Wednesday conditions remain very dry and warm with highs in the mid 70s to low 80s. However, winds will be light and variable, thus negating the need for a fire headline. However, please continue to use caution to avoid fire starts.

Thursday conditions will again be favorable for fire with southerly sustained winds at 25-30 mph and gusts 35-40 mph. A few isolated gusts of 45+ mph are also possible. Additional fire headlines may be necessary. Please check back through the week for updates.

FSD WATCHES/WARNINGS/ADVISORIES

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