textproduct: Sioux Falls

KEY MESSAGES

- Patchy and locally dense fog has developed west of I-29. Fog continues through mid morning, with occasional visibility below one mile. Although risk is very low, areas with temperatures below freezing may see some isolated slick spots.

- Scattered convective showers and isolated thunderstorms may develop Wednesday. Severe storms not expected, but a few wind gusts to 30+ mph may be possible. Scattered sprinkles to showers possible again Thursday.

- The frost/freeze warning program has been activated for the area, with a few areas of concern this week. Thursday night may feature the most concerning temperatures near or below freezing.

- Temperatures will warm above normal by the upcoming weekend into early next week.

UPDATE

Issued at 315 AM CDT Wed Apr 29 2026

Patchy and locally dense fog has developed early this morning west of I-29, mainly in the river valleys, where skies have cleared. Have seen a couple of observations and area DOT cams with visibility below half a mile. Surface temperatures should be warm enough to limit any slick spots, but can't rule out isolated slick spots with temperatures below freezing. Patchy frost is also possible in the northwestern forecast area where temperatures are near/below freezing. May see some patchy fog east of I-29 by daybreak as stratus clears, but confidence is lower in this area. Not anticipating the need for a Dense Fog Advisory as dense fog remains fairly localized.

No other changes to the forecast. Still anticipate convective showers and isolated storms to develop later today with weak instability over the area. With dry air below the cloud layer, wind gusts of 30+ mph are possible with showers and isolated thunderstorms. Northwesterly flow allows additional weak waves to move through the area, keeping shower chances around through Thursday. Cooler than average temperatures prevail leading to nightly risks for frost. Most widespread risks appear to be Thursday night and Friday night. Those with sensitive vegetation will want to keep an eye on the forecast.

DISCUSSION

Issued at 1222 PM CDT Tue Apr 28 2026

THIS AFTERNOON: The passage of mid-lvl vorticity through the Central Plains will continue to bring a risk for sprinkles to very light rain showers into the Tri-State are into the early overnight hours.

TONIGHT: Lingering sprinkles to light showers may continue through very early Wednesday morning, focusing into NW Iowa as the night moves on. Further northwest, depending on clearing, temperatures may fall into the 30s. Have trended temperatures slightly warmer than NBM guidance given increased clouds, as well as the observation that wet ground held temperatures up 1-3 degrees last night. Nevertheless, if Td spreads were a bit more sufficient, patchy frost could develop.

WEDNESDAY-THURSDAY: We'll remain within the influence of a large upper trough rotating through Central Canada and moving towards Hudson Bay by the end of the week. This trough will keep temperatures cooler than normal, but also bring risks for scattered showers through Thursday. A quick warmup Wednesday morning, combined with increasing low-lvl CAA should assist in the development of isolated to scattered showers by mid-day. Soundings show a rather steep low-lvl lapse rate, with a pocket of weak instability suggesting at least isolated thunder mentioning through the afternoon. Winds at the top of the mixed layer are not all that strong, but a pocket of 30+ mph winds in showers could be possible. A similar story for Thursday, with rain chances perhaps more focused in the morning hours and again late afternoon. One hazard to watch will be the overnight low temperatures Wednesday night but especially Thursday night. Cloud cover may prevent any strong drop into Thursday, but with less clouds and light winds Friday morning potential for widespread sub-32 lows will be possible. The probabilities of <32 degree temperatures from both the HREF and NBM are sitting around 50% along the Buffalo ridge Thursday morning. More widespread 40%-60% probabilities of <32 present themselves Friday morning areawide with probabilities of <35 degrees nearly 90+%. All this to say, with the activation of frost/freeze program headlines today, potential is growing for headlines into Friday.

FRIDAY-SUNDAY: The large upper trough swings further east Friday, rebounding temperatures towards the upper 50s with dry weather. Heights slowly rise during the upcoming weekend, signaling a gradual rise in temperatures each day. A pleasant Saturday is expected with highs rising through the 60s. The passage of a weak front early Sunday will have minimal impacts on temperatures with highs again rising into the upper 60s to lower 70s.

MONDAY-TUESDAY: Mid-lvl flow patterns remain split, with a dominant southern stream flow keeping the risks for severe weather and extreme warmup over the southern US. Further north, lingering influence of west to northwesterly upper flow keeps temperatures near to slightly above normal. The passage of another weak front Monday may bring low risks for rain, with greater potential showing up in extended model guidance by the middle of next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1231 AM CDT Wed Apr 29 2026

VFR conditions will prevail through the period with scattered showers/isolated thunder possible this afternoon and evening. Confidence in thunder is too low to mention in TAFs at this time, but would be favored after 29/18Z through sunset. Higher cloud bases could support isolated erratic wind gusts up to 30kt with showers. Otherwise wind speeds should generally remain at or below 12kt through the period with a few afternoon gusts of 15-20kt.

FSD WATCHES/WARNINGS/ADVISORIES

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