textproduct: Sioux Falls

KEY MESSAGES

- A Red Flag Warning remains in effect until 9 pm tonight due to relative humidity values dropping below 30% and strong wind gusts of 30-45 mph.

- A Marginal (level 1 of 5) risk for isolated to scattered rain showers to thunderstorms are possible this afternoon and evening. The greatest risk is wind gusts of 60+ mph.

- A High Wind Warning is in effect tonight from 7 pm this evening until 7 am Friday morning. Northwest gusts could reach 55-65 mph with isolated gusts up to 75 mph possible.

- Snow looks to return on Saturday in a weak band. However, a stronger system is expected to begin to impact the area Saturday evening. This system will persist through the entirety of Sunday before finally exiting the area by early Monday morning.

- Strong winds and heavy snow are in store for this system. Thus, a Winter Storm Watch for Blizzard conditions has been issued for locations along and northeast of a line from Chamberlain, South Dakota to Beresford, South Dakota to Storm Lake, Iowa line. The Watch is in effect from Saturday evening into Monday morning.

DISCUSSION

Issued at 250 PM CDT Thu Mar 12 2026

An active pattern is ahead with confidence for significantly impactful weather increasing. Looking aloft at GOES water vapor we can see the flow aloft is northwesterly with a 140-150 kt jet streak. The exit region of which is located over the Tri-State area through this afternoon and overnight. The resulting wind divergence aloft will further enhance winds in the LLJ as surface convergence increases and pressure falls ahead of an incoming Clipper system. As we begin to mix higher into the boundary layer today we will tap into that 30-40 kt LLJ. Gusts at the surface will increase through the afternoon as a result, reaching 30-45 mph.

The clipper system places us in a strong WAA regime this afternoon. However, there are a few details that may work to limit afternoon highs. Clouds continue to flow in from the northwest, and have advanced further south faster than previously anticipated. There is also a chance for isolated to scattered rain showers and thunderstorms this afternoon and evening, roughly between 3pm to 9pm. Soundings indicate a very dry subcloud layer, which will limit how much actually reaches the ground. However, due to a 10 degree C dewpoint temperature depression, evaporative cooling as rain falls through the dry layer may produced severe wind gusts of 60+ mph. This is outlined in the SPC Day 1 Marginal (level 1 of 5) outlook. Considering this have decided to go with the slightly cooler NBM highs for this afternoon. Along and south of a rough line from Huron to Storm Lake highs will range from the low to upper 60s, warmest along the southern Missouri River Counties. This area is also expected to see the lowest relative humidity values, less than 30%. To the north of that line highs will be in the 50s with higher relative humidity values. Though we have some lingering snow/snowmelt on the ground from yesterday, and the cooler highs today, the low humidity and very strong winds keep Grassland Fire Danger in the Very High to Extreme categories for this afternoon. See the Fire Weather Discussion below for more details.

Our next period of concern comes this evening and overnight as the Clipper system drops southeast into Minnesota. The SPG continues to tighten as pressure falls ahead of the cold front. The LLJ enhances as divergence aloft increases. Temperatures in the mid-levels drop rapidly 6-10 degrees C behind the front. All these factors will work together to produce very strong winds beginning later this afternoon and continuing through Friday morning. By 6pm CDT tonight gusts east of I-29 will be between 25-35 mph. Areas to the west will be seeing gusts 35-45 mph. As we continue into the evening gusts continue to increase and spread southeastward. Widespread gusts of 55-65 mph are expected with isolated gusts up to 75 mph possible. Winds remain strong through 4-6 am CDT when they will begin to gradually taper off through Friday morning, becoming light in the afternoon. Afternoon highs will be cooler thanks to the northwesterly winds brining in cold air, reaching only the mid 30s to 40s.

Saturday will begin with light snow beginning to fall during the early morning hours as warm air advection (WAA) strengthens aloft, tightening the elevated frontal temperature gradient and also strengthen the frontogenesis (FGEN) along it. The dendritic growth zone (DGZ) will also be saturated with sufficient omega (upward motion) in it to support a band of snow. The good news about this band is that not expected to last long as the FGEN will be weakening during the morning hours. Light snowfall is expected with this band which looks to fall across near and north of I-90. Saturday afternoon will be more on the dry side as the upper level wave responsible for additional impacts will be pushing in from the Northern Rockies. High temperatures look to warm to the 30s to up to around 50F during the afternoon timeframe though depending on how much snow falls during the morning hours, highs temperatures could come down a bit.

Chances for snow will be increasing Saturday evening as WAA restrengthens aloft. This in turn will re-tighten the temperatures gradient and thus restrengthen the FGEN along the elevated front. This will be the main show as strong QG ascent resides in the right entrance region of an upper level jet. Snow will expand in coverage through the rest of the evening and entire overnight hours. There could be a small area of mixed precipitation on the leading edge of the band of snow as the WAA just barely pushes temperatures above freezing aloft. The strong front will translate southwards after beginning around the highway-14 corridor. This will quickly cool the warmed temperatures, turning any mixed precipitation back over to snow. The strongest ascent will come during the overnight hours and into early Sunday morning where the latest deterministic guidance shows strong FGEN around 700 mb along with low stability and negative equivalent potential vorticity (EPV) values above the front. Thus, the bulk of the snow looks to fall during this period of time. At the same time, winds will be strengthening as snow fall rates increase. Gusts will be out of the east/northeast with gusts strengthening up to 30-40 mph throughout the night. With such strong winds in place as snow is falling, blowing snow is expected with the falling snow. The best forcing for ascent will be sliding eastwards throughout the morning hours on Saturday. This will gradually end snowfall across the area from northwest to southeast. Though latest trends keep snow chances going through the afternoon timeframe. Winds will turn to out of the north during this period of time with gusts further increasing up to about 50 mph. Snow will have the potential to blow around after snow is done falling. Thus, blowing snow looks to persist for the rest of Saturday even after the snow finishes falling. Thus, have decided to issue a Winter Storm Watch for Blizzard conditions. The Watch is in effect from Saturday evening through Monday morning as the weakening winds will still result in some blowing snow through Sunday night. Snowfall amounts at this time look to be impactful with the ensembles showing a 40- 90% chance for snowfall totals to exceed 6 inches mainly along and northeast of a Chamberlain, South Dakota to Beresford, South Dakota to Storm Lake, Iowa line. The highest probabilities lie across southwest Minnesota. The ensembles spread increases up to a foot of snow where the probabilities span from a 20-60% chance, highest again across southwest Minnesota. This combination of wind and snowfall looks to bring the most impactful winter storm of the season to the area. While details can change heading into this event, please continue to monitor the latest forecast for the most up to date information.

The rest of the next week looks to begin on the cold side and slowly warm throughout the week. There could be additional chances for snow during the middle of the week but details are uncertain.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1257 PM CDT Thu Mar 12 2026

VFR conditions are expected to prevail for this period. Isolated to scattered showers to thunderstorms are possible this afternoon. Storms must contend with a very dry subcloud layer, limiting how much moisture we receive at the surface. Still, some rain is likely to make it through but it will be very spotty in nature and confined mostly along and north of I-90. In addition, thanks to the dry layer, there is potential that storms could produce very strong down draft wind gusts in excess of 52 kts. Storms are expected to exit to the east this evening.

At the same time storms are exiting, a Clipper system will past just to the north of the region. As it does so, surface winds will increase drastically beginning this afternoon and continuing overnight into Friday morning. Frequent gusts of 45-55 kts will be widespread with gusts up to 62 kts possible. Surface winds are expected to very gradually decrease through the afternoon Friday.

Low level wind shear is expected at all three TAF sites as the surface cold front passes through. Shear is expected to begin around 00Z Friday at KHON and progress rapidly southeast through KFSD and KSUX over the next hour or two. Shear is expected to relax after 06Z Friday.

FIRE WEATHER

Issued at 250 PM CDT Thu Mar 12 2026

Southwesterly to westerly winds gusting 30-45 mph coupled with low minimum relative humidity has resulted in Grassland Fire Danger reaching the Very High to Extreme category. Minimum relative humidity values are expected to fall to 25-35% along and south of a line from Huron to Storm Lake line.

High temperatures have trended slightly cooler with this forecast package. Despite that, the very dry air and strong winds could still allow for rapid fire intensification. As such, the Red Flag warning until 9 PM CDT today remains in good shape.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning until 9 PM CDT this evening for SDZ038-050- 052>055-057>071. High Wind Warning from 9 PM this evening to 7 AM CDT Friday for SDZ066>071. Winter Storm Watch from Saturday evening through Monday morning for SDZ040-056-062-067. High Wind Warning from 7 PM this evening to 7 AM CDT Friday for SDZ038>040-050-052>065. Winter Storm Watch from Saturday evening through late Sunday night for SDZ038-039-052>055-057>061. MN...Winter Storm Watch from Saturday evening through Monday morning for MNZ071-072-080-081-089-090-097-098. High Wind Warning from 7 PM this evening to 7 AM CDT Friday for MNZ071-072-080-081-089-090-097-098. IA...Red Flag Warning until 9 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032. High Wind Warning from 9 PM this evening to 7 AM CDT Friday for IAZ001>003-012>014-020>022-031-032. Winter Storm Watch from Saturday evening through Monday morning for IAZ001>003-012>014-021-022. NE...Red Flag Warning until 9 PM CDT this evening for NEZ013-014. High Wind Warning from 9 PM this evening to 7 AM CDT Friday for NEZ013-014.