textproduct: Sioux Falls

KEY MESSAGES

- Patchy fog, especially in river valleys, will lead to visibility below two miles at times through mid morning. Localized dense fog is possible.

- Well above normal temperatures, increasing winds, and drying fuels lead to elevated fire danger Thursday to near critical fire danger Friday. Harvest activity should use extreme caution.

- A significant cooldown arrives this weekend and continues into next week with highs back into the 50s.

- This cooldown brings rain risks Saturday into Monday. Probabilities for >0.10" are near 100%, with potential for >0.50" near 70%, and probabilities for >1.0" as high as 50%.

UPDATE

Issued at 322 AM CDT Thu Oct 22 2026

Beginning to see some fog develop across the area early this morning. Outside of brief visibility below one mile, most locations are remaining at or above two miles. Expect fog to expand over the area as winds become calm and temperatures fall into the 40s to near 50. Fog should quickly mix out by mid morning as southerly winds increase.

Slightly increased temperatures again with the 90th percentile for the next couple of days as the NBM continues to under perform. Other than that, no significant changes to the forecast. Southerly winds increase today, with gusts west of I-29 this afternoon around 30 mph (tapering down as you head east). Elevated fire danger is expected, especially across south central SD. More details below in the fire weather section. Winds remain breezy overnight with the tightening SPG with lows in the 50s.

Latest hi-res guidance continues to show light rain/showers moving through Friday morning on an initial mid level wave/WAA. However, rainfall amounts will be light with low (< 15%) chances of a tenth of an inch or more. Main concern Friday remains the strong southerly winds and warm temperatures, creating near critical fire danger. Wind gusts across the area from 30 to 45 mph expected, highest west of US Highway 81. Soundings continue to show the potential for some stronger gusts in south central SD, with NBM probability of over 50 mph wind gusts around 30% in Gregory county. Expect near critical fire conditions, with the limiting factor humidity values. More details below. Those completing harvest activities should take extra caution Friday to prevent sparks.

Rain chances remain on track for the weekend with cooler temperatures ahead.

DISCUSSION

Issued at 1235 PM CDT Wed Oct 21 2026

THIS AFTERNOON: An absolutely beautiful mid-October afternoon is unfolding as winds have remain light, skies remain clear, and temperatures are rising into the 70s. Dew points are mixing down into the middle 40s in a few areas, which could be a sign for later tonight.

TONIGHT: A bit of high lvl cirrus that crosses the CWA later this afternoon and early evening will prevent a sharp temperature drop- off initially. However nearly all guidance is indicating that we'll see a night with light to calm winds and clear skies. Given these conditions, will lower temperatures significantly in most locations, with HRRR/RAP guidance indicating potential for mid-40s. With afternoon dew points likely falling a bit further, this leaves cross- over temperatures in a favorable position to lead to fog development. The majority of this fog may be confined to sheltered river/valley areas, but given temperature falls, some may spill out into a broader area and become locally dense.

THURSDAY: Troughing sliding into the Central Rockies will help intensify the SPG throughout the Plains on Thursday. Winds will begin to increase early in the morning and by the afternoon we'll see routine gusts 20 to 30 mph at times. Slowly drying fuels and increasing wind will lead to increased fire danger. See separate discussion for further details.

FRIDAY: Late Thursday night we'll begin to see an increase in low- lvl moisture emanating from the Oklahoma Panhandle. This moisture, when combined with convergence on a 40 knot LLJ and weak dPVA, may lead to isolated to scattered high based showers after 3am Friday which will continue lifting northward Friday morning. A minor increase in elevated instability could lead to isolated lightning strikes with this activity. However, the greater threat in the afternoon and evening will be the surging high temperatures and increasing wind gusts. Latest guidance strongly supports sustained winds 20 mph in many locations, with potential for gusts of 45 mph at times. While the SE surface wind direction is a bit mis-aligned with the strongest corridor of low-lvl SWLY flow, the highest wind corridor is likely to fall along and west of a Brookings to Yankton line. This will again increase fire danger so please read separate discussion for further details.

SATURDAY-WEDNESDAY: A warm overnight is anticipated into Saturday as the SPG really doesn't weaken and promotes increased mixing through the night. By Saturday morning, a cold front will slowly slide east into Central South Dakota. Weak low-lvl convergence and moisture streaming ahead of this front could lead to high based showers into daybreak. A splitting upper trough over the Rockies will promote two distinct features, a progressive trough lifting northeast into southern Canada Saturday into Sunday, with a cutoff area of energy stalling over the Four Corners. The aforementioned frontal boundary will get nudged southeast on Saturday, bisecting the CWA. With significant cold air lagging this front, the temperature gradient is not expected to be extreme. However an increase in cloud cover, along with potential for occasional light rain will persist through Saturday and into Saturday night.

One or more weak impulses traveling northeast along the stalled front will keep clouds and occasional rain risks through the CWA Saturday night and through Sunday. QPF amounts through Sunday afternoon may be on the lighter side, with most areas seeing less than 0.25".

That earlier mentioned upper low over the Four Corners begins to eject northeast by the end of the weekend and into Monday. A strong low-lvl frontal zone is expected to develop across the CWA ahead of this system, promoting increasing rain chances. The very slow northward movement of the approaching SW trough will keep high rain chances through the CWA on Monday and will likely continue into early Tuesday. Latest NBM probabilities suggest high rain probabilities at near 100% for >0.10", potential for >0.50" near 70%- 80%, probabilities for >1.0" as high as 50% and probabilities for 2.0" totals at 20%.

The passage of this system, and then the cooler air that follows it, will promote a return of more typical mid-late October temperatures. High temperatures Sunday through Wednesday are favored to be in the upper 40s to mid 50s.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 628 AM CDT Thu Oct 22 2026

MVFR to IFR fog continues through mid morning. A few sites near and along the MO River (mainly near KAGZ to KVMR) have been more persistent with visibility below 1/2 SM; however, other sites have been much more sporadic with vis under 1 SM. Conditions improve by 14-15z, with VFR conditions expected for the rest of the period.

Light and variable winds this morning increase, with southerly gusts 15-25 knots this afternoon and evening. Winds remain breezy overnight, with gusts around 30 knots possible by daybreak Friday in south central SD.

Light rain showers develop toward the very end of the TAF period but too low confidence in impacts to terminals to include at this time.

FIRE WEATHER

Issued at 322 AM CDT Thu Oct 22 2026

Warm temperatures, increasing winds, and dry conditions today will lead to elevated fire concerns - especially west of I-29. By this afternoon, southerly winds increase to 10-15 mph, with gusts 20-25 mph and as high as 30 mph in south central SD. Highs climb to the mid 70s and near 80 degrees. Minimum humidity values above 40% should temper widespread significant concerns today.

Mostly dry conditions continue Friday after some scattered morning showers/sprinkles. Probability of more than a tenth of an inch of rain is low (less than 15%). Southerly winds continue to increase through the morning hours with gusts by the afternoon 30 to 45 mph, highest toward and west of US Highway 81. Gusts around 50 mph are possible (30% or less) in south central SD. These strong winds coupled with drying fuels/crops and temperatures in the mid 70s to lower 80s, will lead to near critical fire conditions over the entire area. Humidity values should remain above critical thresholds (values near/above 35%); however, GFDI values climb into the High and Very High categories. Any fire that starts will likely quickly spread given dry grasses and crops; use extreme caution to prevent sparks.

Locally elevated fire danger may continue into Saturday, although rain chances will be increasing and temperatures cooling as a boundary moves into the area. Rain chances and cooler temperatures prevail into the weekend and early next week, tempering fire concerns.

FSD WATCHES/WARNINGS/ADVISORIES

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