textproduct: Sioux Falls

KEY MESSAGES

- Chances for fog along river valleys and low areas return Wednesday morning. Area most likely to see fog is the northern James River with a 50% probability of visibility decreasing to 2 miles or less.

- Above to well above average temperatures continue. Highs in the upper 60s and 70s and lows in the 40s and 50s. Average highs for mid/late October are upper 50s to lower 60s, with average lows in the mid to upper 30s.

- Dry conditions are expected through Thursday evening. Low (35% or less) rain chances return Friday morning with more widespread and higher chances (around 50%) this weekend.

- Warm, dry, and breezy conditions lead to localized elevated fire danger for the rest of this week.

DISCUSSION

Issued at 313 PM CDT Tue Oct 20 2026

Breezy southerly winds will gradually decrease this afternoon and evening with mostly clear skies. Lows will fall to the mid to upper 40s. For reference average lows this time of year are in the mid 30s. Early Wednesday morning winds will become light, which may allow for patchy fog development along river valleys and low areas. Especially along the northern James River Valley where probability of visibility falling to 2 miles or less is around 50%. Any fog development will burn off by mid-Wednesday morning.

As for the rest of Wednesday an upper trough and surface low located over eastern Nunavut and Manitoba will drag a cold front into the region early Wednesday morning, connected to a secondary weak mid- level shortwave and surface low over western South Dakota. At the same time moderate WAA on southerly winds will begin to amplify a shallow upper ridge located over the south central US. As this ridge continues to amplify through the day it will push back against the cold front causing it to stall out, eventually washing out the front and secondary low pressure. This will result in a diffuse weak surface boundary. Winds may vary along this boundary for a short time before becoming southerly once again as a surface high pressure strengthens over the central Midwestern states. By Friday 200 mb heights will be near to or at maximum for climatology, as will 700- 500 mb temperatures. What this means is at the surface we will be experiencing abnormally warm October days. The NBM continued showing a cold bias this run and so coordinated with neighbors to boost highs using a blend of NBM/NBM90th. Highs will rise into the low to mid 70s Wednesday, and the mid to upper 70s Thursday. There may even be a few 80s! While this is 10 to 20 degrees F warmer than average, we are still more than 5 degrees away from tying or breaking any record highs.

Looking now to the west we see a deep upper trough moving on shore stretching from British Columbia down to southern California. As this and a series of embedded shortwaves on the west side of the ridge move east the SPG will begin to tighten. Southerly winds will increase, gusting 15-25 mph by Thursday afternoon for areas along and west of I-29. East of I-29 gusts will 15 mph or less. As this entire pattern shifts east overnight gusty winds will spread east. Friday winds will continue to increase, with widespread gusts of 30 to 40 mph. Higher gusts are expected as you move west toward central South Dakota. Gusts west of the James River could reach 45+ mph. While minimum relative humidity values will remain above 40%, strong winds and drying grasses will lead to locally elevated fire risk at times through the remainder of the week.

In addition, early Friday morning WAA along the nose of the LLJ may result in light, scattered showers over south central South Dakota early Friday morning moving northeast into southwest Minnesota around noon. These showers are likely to be hit and miss, meaning not everyone will get rain, and those that do will probably only see a trace to a hundredth or two. Friday night into Saturday as the previously mentioned upper trough moves into the central plains of Canada and the US, draping a cold front down into eastern Colorado. Showers will form along the front and move southeast from early Saturday morning through Saturday evening. Once again showers are expected to be light, and could be spotty at times. A brief break overnight before a southern stream upper trough moves northeast into the region bringing more chances for rain Sunday afternoon into Monday morning. Overall totals are expected to be light, with areas of southeast South Dakota, northeast Nebraska, and northwest Iowa seeing around a 60% probability of 0.25 inches. Probabilities fall off quickly from there, and most will only see a few hundredths to a tenth or so.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1234 PM CDT Tue Oct 20 2026

VFR conditions with mostly clear skies are expected to prevail for this period. Breezy south-southeasterly winds will continue to gust 15-23 kts through the remainder of the afternoon. Winds will then gradually decrease, becoming light and variable after midnight tonight.

Light and variable winds may allow for patchy fog to develop along river valleys and other low areas. Short term guidance indicates the most likely area to see fog is along the James River valley and west. Here visibility may decrease to IFR at times. Should fog develop it is expected to burn off by mid-Wednesday morning. The remainder of the period winds remain southerly and light with few to scattered high level clouds.

FSD WATCHES/WARNINGS/ADVISORIES

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