textproduct: Sioux Falls

KEY MESSAGES

- Isolated strong to severe thunderstorms are possible tonight into Friday morning, and again Friday afternoon and evening. Main threats with both rounds is hail to quarter size, with wind gusts to 60 mph the secondary threat.

- Rain is expected to transition to a wintry mix - including freezing rain - then to snow overnight Friday. Snow tapers off by mid-morning Saturday.

UPDATE

Issued at 240 AM CST Thu Mar 5 2026

Fog, including locally dense fog, has developed early this morning. Visibility below 1/2 to 1/4 of a mile has been observed in dense fog, which is mainly occurring along and west of the stratus deck. Will continue to monitor to see if this becomes more widespread and if the Dense Fog Advisory west of I-29 needs to be extended or expanded. Temperatures near to just above freezing could lead to some isolated slick spots in fog through the morning commute.

Forecast today into Saturday remains largely unchanged from the previous shifts. Warm and breezy today with elevated (Very High) fire danger in the west this afternoon and evening. Trough ejects out of the Rockies later today with the first piece of energy moving into the area tonight, which allows showers/storms to develop. Still have the potential for some severe storms south of I-90. Timing tonight after midnight, and may continue through 8 AM. Again, think the big question will be instability (most guidance still around 500 J/kg with some toward 1000 J/kg), but forcing from the strengthening LLJ may be enough to overcome this. Hail to quarter size remains the main threat thanks to steep mid level lapse rates, but can't rule out a gust or two around 60 mph.

Latest hi-res guidance remains quite varied on the coverage of showers through the day Friday but do expect the area to see on and off showers and possibly storms. Severe threat Friday depends on how quickly the front moves through and therefore where the better instability sets up. 05.00z guidance is quite varied on the timing of the front with about 6 hours difference in Sioux Falls with the fropa in the NAM around 15z and the GFS around 21z on Friday. Additionally, better moisture may be shoved off to the south and east, which would limit both coverage of precip and severe potential. Greatest severe risk would be during the afternoon and early evening hours across our southeast CWA. Main threat again will be quarter sized hail, but a rogue wind gust to 60 mph can't be entirely ruled out. Confidence is low on timing, but think 1-7 PM is the highest chances for severe.

Falling temperatures will allow for a transition to snow, with a mix including freezing rain as we switch over. Similar concern with moisture for the snow potential late Friday into Saturday. Latest guidance still generally keeps the wave open as it moves through, so unsure how strong any deformation band might be on the back side - and guidance reflects this uncertainty. If there's not much moisture to wrap around and forcing is more broad, amounts should remain light. 30% chance or less of more than 2 inches along a line from Burke to De Smet. Ice accumulations of a light glaze are possible as we transition to snow.

DISCUSSION

Issued at 204 PM CST Wed Mar 4 2026

Stratus is expected to linger for areas east of I-29 late this afternoon and evening. This will likely work to limit our afternoon highs in that area. Have adjusted them down slightly with a blend of NBM and CONSShort. Overnight weak moisture advection on light southerly to southeasterly winds may result in another round of patchy dense fog. Most guidance keeps fog roughly east of the James River. However, some soundings indicate patchy fog may be possible as far west as central South Dakota. Will monitor conditions to see if any headlines are needed.

Tonight a low pressure system skirts to our southeast. While the main area of forcing and rain will be well south of our region, a weak band of positive vorticity advection and WAA may be enough to trigger light sprinkles to light rain over portions of northwestern Iowa and southwestern Minnesota. Confidence in sprinkles is low due to a wide variance in track of the system. Used a blend of NBM and HRRR to get mention of sprinkles into the forecast. Very little accumulation is expected, enough to wet the sidewalk up to a tenth of an inch. Overnight lows will fall to the mid 30s.

For the rest of Thursday expect partly sunny skies and breezy southeasterly winds. Gusts west of I-29 will peak in the afternoon around 25-35 mph, with slightly lower gusts of 20-25 mph expected to the east. Highs will be warm in the upper 50s to 60s. This coupled with the gusty winds will result in areas of central to eastern South dakota and Nebraska experiencing High to Very High Grassland Fire Danger. The good news is minimum relative humidity values will remain above critical thresholds, in the upper 30% or higher. The bad news is if a fire can start, the winds could rapidly accelerate fire through the dry grasses and field stubble. Please use caution with sources of sparks.

In addition, through the day Thursday a deepening mid to upper level trough will progress east through the Rocky Mountains. As it exits out onto the central Plains rapid lee cyclogenesis will couple with an increasing LLJ to bring chances for convection to the region. The latest 12Z runs of the GFS, EU, CAN, and NAM all show this wave sweeping northeast through our region. Ahead of it lapse rates sharpen steeply and MUCAPE increases to between 500-800 J/kg. The 0- 6 km bulk shear has also increased to greater than 45 kts. Given these conditions, elevated strong to severe thunderstorms are possible along and south of I-90 early Friday morning. Primary threat will be hail to the size of pennies (3/4 inch) to quarters (1 inch). Though less of a concern wind gusts in excess of 60 mph are also possible. This threat is covered well by the SPC day 2 outlook.

Rain and thunderstorms remain in the forecast for the majority of the day Friday as a cold front moves through the region. As it does so winds become northerly and increase behind the front. Widespread gusts of 25-35 mph are expected with isolated gusts up to 40 mph possible. Convective parameter's increase through the afternoon and by Friday evening another round of strong to severe thunderstorms is possible. The question with this second round is location of the most favorable conditions. While the track of the storm is fairly consistent across guidance, the location of the best forcing varies from I-29 to the southeast, to southeast of Highway 60. Main threat again will be penny to quarter sized hail with 60+ mph gusts possible. This round is highlighted in the SPC day 3 outlook.

From here guidance begins to diverge on the evolution of the wave. The GFS has the mid-level wave wrapping tightly into a closed low that cuts through the heart of our region. The EU, CAN, and NAM maintain an open wave. All indicate a period of transition on the backside from rain to a wintry mix to all snow late Friday night into early Saturday morning. The GFS indicates a potentially significant band of snow, while the others indicate accumulating snow, but to a much lesser extent. At this time uncertainty is too high to speculate on totals, however confidence is high that most of the region will see at least some accumulating snow. While winds overnight will decrease they will continue to gust 20-30 mph during the period when snow is expected to be falling. Some reductions in visibility due to blowing and drifting snow are possible.

The system is expected to exit northeast of the region by late morning Saturday. Clouds will decrease and highs will warm into the 40s. For Sunday winds will gradually become southwesterly ushering in a much drier air mass and warmer temperatures. Highs will climb into the 60s with a few 70s possible. Monday will be similar with even more WAA increasing afternoon highs into the 60s and 70s along and south of Highway 20. Monday afternoon a cold front moves through the region turning winds northerly and bringing periodic chances for rain and snow through mid-week. Highs Tuesday will be in the 40s and 50s, while Wednesday they will fall into the 30s.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1146 AM CST Thu Mar 5 2026

VFR ceilings for areas to the west of I-29 this afternoon. Low stratus continues to scatter out east of I-29, where LIFR to MVFR ceilings will improve as it does so. Mid to high level clouds are flowing in from the west southwest ahead of an incoming wave this evening. Breezy southwesterly winds will continue to gust 20-30 kts this afternoon for areas west of I-29, 17-20 kts to the east. Winds gradually decrease through the evening but remain slightly breezy overnight with gusts of 15-20 kts. A cold front is expected to enter our region from the west around 06.12Z. This will turn winds to the northwest as they become gusty behind the front. The strongest gusts of 25-35 kts will be along and west of the James River Valley. Gusts spread east through the afternoon but will be lighter at 20-25 kts. There is some uncertainty as to when the front will pass through KFSD. Some CAMs show it passing through as early as 06.15Z, while others have the passage slower around 06.20Z.

This evening rain showers are expected to develop east of the James River Valley. As the low level jet increases some of these storms may increase to strong to severe thunderstorms. Main timing of will be after midnight east of I-29, with the main threat being brief heavy downpours, hail the size of quarters, and an isolated gust or two of 50+ kts. As thunderstorms move out around daybreak, scattered to numerous rain showers move in from the west, continuing through the end of the period.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.