Sioux Falls, SD 57105 Weather

Key Messages

- Very isolated river valley fog will lead to visibility below two miles at times into the morning commute.

- 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 (25% 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, with more widespread concerns by late week.

Update

Issued at 250 AM CDT Tue Oct 20 2026

Winds early this morning remain around 5-10 mph, which should limit any fog development through daybreak. However, can't entirely rule out some very patchy river valley fog which could reduce visibility. Otherwise, a pleasant morning with temperatures in the upper 30s to upper 40s and clear skies.

Once again, raised highs from the blend for Tuesday through Thursday using the 90th percentile, which results in increases of 2-5 degrees across the area. The main impact to this is resultant humidity values which would impact fire weather, as well as warmer conditions helping to dry grasses. Highs each day in the upper 60s to upper 70s, warmest toward late week. With periodically breezy conditions and drying fuels, elevated fire danger may become more widespread late week. Dry weather prevails through mid week, with rain chances returning early Friday morning, higher chances into the weekend.

Discussion

Issued at 200 PM CDT Mon Oct 19 2026

A few high cirrus clouds and light southeast winds will result in a very pleasant fall evening. Weak WAA overnight will keep our lows warm for this time of year, in the low to mid 40s. (Average is mid 30s) Early Tuesday morning some patchy valley fog is possible, especially for areas along and west of the James River Valley. Here ensembles indicate a roughly 20-40% probability of visibility falling to 2 miles or less. Any fog that forms will be short lived and will mix out quickly as winds begin to increase after sunrise.

Tuesday an upper ridge broadens and shifts east over central and eastern CONUS. Surface high pressure settles over the Great Lakes region, and winds will become southerly. At the same time a mid- level wave along the western US/CAN border will push southeast. As it does so the SPG at the surface will tighten and winds will increase and become breezy. By mid-Tuesday afternoon gusts of 15-25 mph are expected with the highest winds along and west of the James River Valley. Occasional gusts up to 30 mph are possible in south central South Dakota. The NBM continues to have a low bias where high temperatures are concerned. After coordination with neighbors, boosted highs with a blend of NBM/NBM90. Highs for Tuesday are expected to climb into the upper 60s to low 70s, with averages for this time of year in the upper 50s to low 60s.

While minimum relative humidity values will remain well above critical (near 40% or greater) the warm and dry conditions will result in the Grassland Fire Danger Index elevating to the moderate category for areas along and west of I-29 Tuesday. The main concern for fire will be in the fields themselves as harvesting operations continue. Warm, dry, and periodically breezy conditions are expected to continue through the week, keeping Fire Danger slightly elevated. Please use caution and report any fires immediately.

Early Wednesday morning the previously mentioned wave will drag a weak cold front through the region. Guidance has continued to back off on rain chances with the front, keeping any rain that forms well south of our CWA. Winds will change from southerly to southeasterly as the front moves through in the afternoon. Highs for Wednesday will again be well above average in the low to mid 70s.

Through the overnight and continuing on into Friday strong WAA in the mid levels will work to sharply amplify the upper ridge. Heights aloft will rise to near the maximum of climatology. At the surface we can expect clear skies and warm highs in the mid to upper 70s both Thursday and Friday. Winds will also be increasing beginning Thursday afternoon as a deepening upper trough off the western coast moves inland. The tightening SPG will result in afternoon wind gusts out of the south-southeast at 15 to 25 mph. Strongest winds will be along and west of I-29, with occasional gusts to 30 mph possible over central South Dakota. Gusty winds move slowly east through the overnight and into Friday. By noon widespread gusts of 25 to 35 mph are possible. Once again the strongest winds will be located over central South Dakota where gusts in excess of 45 mph are possible. Winds decrease gradually through the overnight, but continue gusting 20-30 mph through early Saturday afternoon.

Aviation

Issued at 613 AM CDT Tue Oct 20 2026

Very isolated river valley fog will lead to some brief MVFR/IFR conditions into mid morning, with a couple sites dropping to around two miles at times. Outside of fog, VFR conditions are expected.

South-southeasterly winds increase this morning, with gusts around 20 to 25 knots (highest across south central SD). Winds taper off late tonight, becoming light and variable toward daybreak Wednesday. Very patchy fog may develop again toward the end of the period.