textproduct: Sioux Falls

KEY MESSAGES

- Periods of light to moderate showers late tonight through Friday bringing beneficial rainfall to the area. A quarter of an inch up to an inch is expected. Portions of northeast Nebraska and northwest Iowa may see 1.25 inches.

- Severe weather is not expected with these showers, however a few rumbles of thunder are possible. If you have outdoor plans ensure you know where your nearest shelter is.

- Below normal temperatures will continue through Saturday before warmer conditions return from Sunday onwards.

DISCUSSION

Issued at 230 PM CDT Thu May 21 2026

Scattered clouds will increase late this afternoon ahead of an approaching upper trough and embedded shortwave. Good mixing will allow southeast winds to tap into a modest LLJ. Resultant afternoon winds will be breezy gusting 20-25 mph. Winds decrease slightly after sunset but remain on the breezy side overnight gusting to 20 mph. Highs today will be cooler, in the 60s and 70s. Overnight lows look to fall to 40s. Chances for showers increase late this afternoon and evening as the previously mentioned short wave enters south central South Dakota. Isolated to scattered showers will gradually flow in from the south, expanding in coverage across most of the region by sunrise. Severe weather is not expected.

Beginning very early Friday morning plentiful moisture will advect north thanks to a weak theta e ridge and pool ahead of an approaching cold front. Despite the push of warm and moist air, instability remains low, generally less than 300 J/kg. However, this is enough for a few rumbles of thunder. By Friday mid- morning a region of enhanced vorticity enters central South Dakota and WAA and the LLJ ramp up. The increased forcing will result in scattered showers becoming more numerous and broader in areal coverage. Lightning risks increase as well. Periods of heavier rainfall may occur, up to around 0.25 inch per hour. As the cold front continues to progress east Friday afternoon a region of strong vorticity advection associated with the surface low will work to focus storms into a more organized convective line. A few stronger storms may produce frequent lightning and wind gusts up to 40 mph, but severe weather is not expected. Brief heavy down pours are possible under any of the stronger storms that form. The more organized line looks to set up just to the west of I-29 and progress eastward between 2 and 10 pm CDT. Storms should push east of the region shortly after midnight. Additional light showers are possible as moisture wraps around the low, mainly along and north of Highway 14 Saturday morning. Very little additional accumulation is expected. HREF LPMM indicates rainfall totals of a quarter of an inch up to 1 inch for the majority of the region. Portions of northeast Nebraska and northwest Iowa could possibly see 1.25 inches plus. Guidance has in general been trending totals up the past few runs, if this trend continues some areas may even see up to 2 inches.

Winds continue to increase through Friday afternoon as the SPG tightens further. Peak winds are expected in the late morning to early afternoon. Widespread gusts of 25-30 mph are expected with occasional gusts to 35 mph possible. Winds will decrease after sunset, becoming light overnight. Highs for Friday will be cool in the 50s to low 60s. Lows will be in the 40s.

Saturday, mostly cloudy skies will become scattered through the day. Winds will be light and highs will be slightly warmer in the upper 60s to mid-70s. A few isolated light showers are possible in the very early hours Sunday morning as an upper wave axis crosses through the region. Very little accumulation is expected. Showers end shortly after sunrise. The rest of Sunday will be beautiful day with mostly clear skies and highs in the upper 70s to low 80s. Afternoon southerly winds will be on the breezy side, gusting around 20 to 25 mph.

Late Sunday night into Monday morning another round of showers and thunderstorms are possible as an upper wave and WAA make their way through the region. While convective parameters are generally good, confidence in strong storms is low due to a wide variance in guidance. Showers should clear out Monday late morning. Highs will be in the 80s and 90s with breezy afternoon southerly winds. From Tuesday onward an upper ridge will build over the region. Dry conditions are expected to prevail with highs in the 80s. By Thursday night a more progressive upper wave may move through the region. But details are uncertain at this time.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1235 PM CDT Thu May 21 2026

Mostly VFR conditions for the first half of this period. Breezy southwest winds gusting 22-25 kts will continue through the evening. Though winds will decrease overnight, they will remain on the breezy side ahead of an incoming frontal system. After sunrise winds will increase again as the front approaches with gusts of 25-30 kts in the late morning to early afternoon. Breezy winds continue through the end of the period.

Scattered clouds, mostly east of I-29, will lift a bit more this afternoon. Clouds will then begin to thicken and ceilings lower late this evening into the overnight as the previously mentioned frontal system brings widespread showers and thunderstorms to the region. Severe weather is not expected, however periods of heavy showers will decrease visibility and ceilings to MVFR and IFR at times. Toward the end of the period the most organized showers and thunderstorms are expected. During this time ceilings may decrease briefly LIFR, but confidence was not high enough to include that in the TAF at this time.

FSD WATCHES/WARNINGS/ADVISORIES

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