textproduct: Sioux Falls

KEY MESSAGES

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

- Critical fire danger expected Tuesday 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. Thursday and Friday warm into the mid 80s to lower 90s.

- Dry weather continues this week. Uncertainty remains, but chances for showers and storms are steadily increasing for late week into the weekend.

UPDATE

Issued at 908 PM CDT Mon May 11 2026

Keeping an eye on temperature trends this evening, with temperatures still in the 70s and lower 80s. Do expect temperatures to fall into the 50s tonight with WAA and southerly winds overriding dew points in the 30s and 40s. Main change to the forecast this evening was to refine coverage of pops and sprinkles/showers tonight into Tuesday morning based on some of the latest CAMs. Biggest question remains how much will even reach the ground with soundings showing a stout sub cloud layer, so coverage may still be too robust. Reflectivity has increased over the last hour by Winner, SD but have not seen any indication that anything has reached the ground. With the refinements to pops, did update cloud cover as well with some guidance struggling in coverage of high clouds. Still partly to mostly cloudy skies tonight.

Gusts have tapered off this evening, but expect winds to remain breezy with gusts returning with the cold front and CAA tonight. No changes at this time to tomorrow's forecast or headlines - Red Flag Warning in effect from noon to 9 PM CDT Tuesday. Not expecting the need for any wind headlines, but may need to reconsider if winds trend higher.

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1217 AM CDT Tue May 12 2026

Isolated sprinkles and showers have developed, with very isolated lightning strikes. Confidence is low in impacts to terminals for both showers and TS, so omitting mention. KFSD may see some VCTS before 07z, but again, too low confidence to include. VFR conditions are expected, and RA may be hard to come by with the very dry sub cloud layer.

Winds are the main concern through the period as a cold front moves south across the area overnight. Sfc winds shift from southerly to northwesterly, with gusts increasing to 30-35+ knots during the day Tuesday. LLJ this morning leads to LLWS as the winds shift both at the sfc and aloft with the jet.

VFR conditions continue through the day Tuesday and into Tuesday night with high clouds around the region. Winds taper down after sunset, becoming light and somewhat variable toward the end of the forecast period.

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 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.