textproduct: Sioux Falls

KEY MESSAGES

- Frost and freeze conditions continue this morning with temperatures falling into the 30s across the area. Freeze Warning and Frost Advisory remain in effect until 8 AM CDT.

- Very patchy fog this morning may reduce visibility to below one mile at times. Fog dissipates by mid morning.

- Scattered showers return this afternoon mainly west of the James River Valley with light accumulations expected.

- Cooler conditions continue this week. Another round of showers and isolated thunderstorms is expected from Thursday afternoon through Friday. Severe weather not expected. However, some ensemble guidance suggests up to a 40 percent chance for a half an inch of rain during this time.

UPDATE

Issued at 245 AM CDT Wed May 20 2026

Calm winds and mostly clear skies are allowing temperatures to plummet into the mid 30s to lower 40s, with lows still expected to fall into the lower/mid 30s across the area. Freeze Warning for portions of the US Hwy 14 corridor and Frost Advisory elsewhere remain on track. A couple of sites across northwestern IA and southeastern SD have developed fog early this morning, leading to visibility below one mile at times. Expect fog to lift by mid morning.

Forecast for the rest of the day remains on track as the next mid level waves moves out of NE. CAMs still show some showers west of the James River later today into tonight, with some weak instability through the saturated layer. Dry sub cloud layer with bases around 5k ft might limit how much reaches the surface, especially with surface high pressure meandering east today. Highs warm into the lower/mid 60s with increasing clouds. This is about 10 degrees below normal for late May.

DISCUSSION

Issued at 1245 PM CDT Tue May 19 2026

Cool high pressure settles into the area tonight and will bring a very good chance for temperatures tall to or below 35 for most of the area with temperatures at or below freezing possible north of I- 90. Thus a freeze warning is in place for highway 14 and nearby locations in SD with a frost advisory for the remainder of the area.

Isolated pockets of fog will be possible early Wednesday morning but at this time it does not appear as though it will become more widespread.

A weak wave will move through the area on Wednesday which could bring a few sprinkles but overall should mainly be an increase in mid level clouds. Otherwise slightly more mild temperatures are expected as southerly flow develops and brings highs back into the 60s for most locations.

Another weak wave moves across NE on Thursday and could bring some light showers to the Missouri River corridor into northwest IA. Precipitation amounts will be light as moisture with the system is very limited.

A bit stronger and more negatively tilted system will swing through on Friday bringing the next best chance for rainfall. Instability very minor with CAPE values generally 500 J/kg or less. The model soundings do indicate the potential for some efficient rainfall however so maybe some half inch or so amounts will be possible. The latest ensemble output indicating about a 10 to 30 percent chance for more than a half an inch and the latest Nam is indicating a couple of areas with more than a half an inch. Long story short, only minor impacts expected with no severe weather.

As this system moves northeast and out of the area a few lingering showers will be possible on Saturday, but warmer temperatures will begin to work into the region. Sunday through the middle of next week will see troughiness to the west and ridging to the east, leaving the area in warmer southerly flow. While there is very little agreement, there should be a couple of weaker waves that could bring showers and thunderstorms to the area, but for now confidence is too low to include in the forecast. Otherwise highs should be in the 80s with lows mainly in the 50s Monday through Wednesday.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 619 AM CDT Wed May 20 2026

Patchy fog has developed this morning, reducing visibility below one mile at times. Outside of far southeastern SD and through northwestern IA, vis below one mile has been fairly brief or sporadic. Fog lifts through mid morning.

Once fog lifts, VFR conditions are expected area wide. A few showers are possible west of the James River later today, but not anticipating any significant impacts. Mid clouds will increase through the latter half of the period. Breezy winds expected west of the James with gust around 20 knots.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Frost Advisory until 8 AM CDT this morning for SDZ050-054>071. Freeze Warning until 8 AM CDT this morning for SDZ038>040-052- 053. MN...Frost Advisory until 8 AM CDT this morning for MNZ071-072-080- 081-089-090-097-098. IA...Frost Advisory until 8 AM CDT this morning for IAZ001>003- 012>014-020>022-031-032. NE...Frost Advisory until 8 AM CDT this morning for NEZ013-014.