textproduct: Sioux Falls

KEY MESSAGES

- Moderate confidence in fog redeveloping tonight across much of the region. It may be dense at times resulting in visibility reductions to less than 3 miles at time.

- Potentially strong to severe thunderstorms are possible Thursday evening into Friday morning, and again Friday afternoon and evening. Main threats with both rounds is hail the size of pennies to quarters, and possibly a wind gust of 60+ mph.

- Rain is expected to transition to a wintry mix before becoming all snow overnight Friday. Snow tapers off my mid-morning Saturday.

UPDATE

Issued at 1045 PM CST Wed Mar 4 2026

Low level stratus continues to sit over locations along and east of I-29 this evening. This stratus looks to sit over this area for the rest of the night as southerly flow keeps it locked in place. The stratus could expand towards the west so will keep an eye on it through the night. The bigger concern for the overnight hours is the potential for another round of fog to develop. Currently, locations to the west of I-29 are clear. The main uncertainty regarding fog development is winds. The surface pressure gradient will be tightening a bit more through the overnight hours, keeping light southeasterly winds going. This could be just enough to prevent radiational fog from forming. At the same time, fog has already developed across southeastern North Dakota and is pushing southwards. The fog appears to be behind a weak boundary. If this boundary can make it into the forecast area, then advection fog is possible. Will be watching this potential advection fog very closely.

Any remaining stratus and fog will burn off during the morning hours on Thursday. Winds will further strengthen by the afternoon timeframe with gusts up to 20-35 mph. High temperatures will warm to the upper 50s and 60s while humidity values drop to 30-60%. The warmest temperatures and lowest humidity will occur across central and south central South Dakota. Thus, elevated fire danger is expected in this area for the afternoon hours. While fire danger will come to an end by the evening timeframe, things will change as a stronger upper level wave pushes eastwards through the Rocky Mountains. This wave will strengthen the low level jet (LLJ) and transport low level moisture northwards. Broad warm air advection (WAA) is expected which looks to result in widespread showers across the area Thursday night. With sufficient enough moisture in place, minor CAPE values look to develop. Could see CAPE values up to 500- 1,000 J/kg at the highest. Thus, think the forecast remains on track that showers and storms will develop. Any severe threat will be tied to large hail with this set up. Hail up to the size of pennies and even a quarter (1 inch) is possible before broad rain showers encompass the majority of the forecast area, using up the available instability.

Showers and remaining weak storms will persist through the morning hours on Friday and even through the afternoon timeframe. This will result in widespread cloud cover for the entire day on Friday. At the same time, a cold front will be pushing through the area throughout the day as well. High temperatures look to span a wide range from the 40s to the 60s. The greatest uncertainty is how fast the cold front will push through the area. If the front pushes through at a faster rate of speed, then little if any severe weather threat would develop and highs will be much cooler. If the front slows down, then high temperatures will be warmer and a severe weather threat could materialize. Latest CAMS have been pushing the front through more quickly, thus keeping severe chances low. The ensembles are also generally in agreement in a faster moving cold front. The exception is the GFS as it is the only model with a closed upper level low and thus keeps the front's speed slower. Will keep an eye on trends over the next few days. The other component to Friday is falling temperatures behind the cold front. With cold enough temperatures in place, precipitation looks to transition from rain to snow with perhaps some mixed precipitation in the forms of freezing rain and sleet in the transition zone. Amounts are still uncertain, especially if the open wave solution comes to fruition and ends up diverting more of the moisture away from the elevated front. For now, the ensembles show a wide range of probabilities from a mere 20% to up to a 70% chance for snowfall totals to exceed 1 inch. The high probabilities is driven by the GFS ensemble.

Any snow will come to an end overnight Friday into early Saturday morning. This will leave the rest of Saturday dry with cooler, but still above average temperatures in the 40s for highs. Zonal flow takes over for Sunday, allowing for high temperatures to warm back to the 50s and 60s. With the pattern persisting aloft, Monday looks to be a repeat with highs again in the 50s and 60s.

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 /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1045 PM CST Wed Mar 4 2026

Latest satellite shows MVFR stratus sitting along and east of I-29 late this evening. This stratus will continue to sit over this area and potentially expand to the west a bit. At the same time, fog remains possible tonight as well. Uncertainty remains in how expansive the fog will be. In fact, latest guidance has backed off on fog chances. Thus, have removed any fog/mist from all TAFs. Fog could be included in if confidence increases in the development and expansiveness of the potential fog. Any fog that does form will burn off during the morning hours tomorrow along with the low level stratus as well. Winds will strengthen by the afternoon timeframe with southeast winds gusts up to 15-30 knots, strongest west of I- 29. Winds will remain breezy through the evening hours but chances for rain look to begin to increase towards the end of the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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