textproduct: Sioux Falls

KEY MESSAGES

- Patchy early morning fog mainly south of I-90, but persistent dense fog is not expected.

- Drier and seasonably mild conditions will dominate the week ahead with only very minor chances for showers into early next week.

UPDATE

Issued at 420 AM CDT Thu Oct 1 2026

Showers did push as far north as portions of Highway 18 in northwest Iowa early this morning with KSPW recording a little over 0.25" rainfall & several personal weather stations showing amounts of 0.50" to locally 1.00" southeast of a Sioux City to Spencer line. Heaviest rain of 4 to 8+ inches remained south of the forecast area and no flooding issues have been noted in our area.

This rain is exiting the far southeast corner of the CWA as of 4 AM, and dry conditions are expected to be much more prevalent through these first several days of October. Cannot rule out a few light showers/sprinkles with some weak instability ahead of a cool front Saturday. However, moisture is limited within the latest forecast soundings and potential for measurable rain has decreased as a result.

Today will be a breezier day behind a weak cool front dropping southeast, with highs today and Friday in the upper 50s and 60s. A surface ridge moving east into the area tonight will allow the breezy winds to decrease quickly with sunset. Lighter winds and clearing skies, along with drier low level air (dew points are forecast to fall through the 40s today with some mid-upper 30s dew points possible north of I-90 tonight), could allow temps to fall near 40 degrees in portions of southwest Minnesota by early Friday. Farther west, some increase in mid-level clouds should hold temps in the mid-upper 40s tonight. At this point it does not look like frost will be a concern in our area tonight, but later shifts may need to watch portions of southwest Minnesota and perhaps back toward the I-29 corridor north of Sioux Falls, as the latest NBM does show low (20% or less) probabilities of low temperatures reaching 35-36F tonight.

DISCUSSION

Issued at 111 PM CDT Wed Sep 30 2026

All indications continue to point towards keeping the heavier rain to the south later this afternoon and tonight. The high resolution models only bring about a quarter of an inch of rain to southern parts of Woodbury and Ida counties with the ensemble output showing about a 20-40 percent chance to exceed 1 inch of rain, the EC probabilities a little higher. With 3-4 inches of rain needed to make any if the rivers really move upwards, flooding concerns are very minimal.

Fog will again be possible later tonight into Thursday morning, but for now the model soundings suggest the lower level saturated layer is much shallower, so a better chance to burn off more quickly in the morning. A surge of drier air will build southward with dew points falling into the 40s through the morning. Also looks like the better chances would be over parts of northwest IA and nearby locations.

A system will move by to the north Friday into Saturday. While this will bring some mid level cloud cover into the area, precipitation chances will remain fairly low with dry air below about 800 mb. Some very weak instability aloft Friday night into Saturday ahead of an incoming shot of cooler and drier air may see the need to add some spotty showers during this time, but confidence fairly low in this weak instability. Without the weak instability, saturation looks to occur below the dgz so rainfall would not be expected without the instability. Overall impacts will be very minor.

Upper level ridging builds into the area Sunday into Monday ahead of the next wave. This wave will bring small chances for showers Monday night into Tuesday, but again very low confidence fighting drier air with the wave well to the north. One thing that this wave will bring is mild weather to the area. Looking at highs Tuesday and Wednesday around 70 in most locations. Highs more in the lower to mid 60s are expected this weekend.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1107 PM CDT Wed Sep 30 2026

Rain over northwestern Iowa, far northeast Nebraska, and far southeast South Dakota will continue to slide eastward through the remainder of the night, ending from west to east Thursday morning. Patchy fog also remains possible mainly over northwest Iowa (40% chance) through about sunrise. Any dense fog should remain highly localized. After the rain and any fog early this morning, VFR conditions are expected through the remainder of the period.

Winds will gradually increase out of the north-northeast through the morning hours today, with a few gusts to around 20 to locally 25 kts during the daytime hours. Winds will diminish through the late afternoon and evening Thursday.

FSD WATCHES/WARNINGS/ADVISORIES

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