textproduct: Sioux Falls

KEY MESSAGES

- Periods of light to moderate showers late tonight through Friday bringing beneficial rainfall to the area. While exact amounts are uncertain, chances for over half an inch remain is moderate to high (50-75%).

- Very isolated thunderstorms are expected; severe weather remains unlikely and not expected.

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

UPDATE

Issued at 259 AM CDT Thu May 21 2026

Precipitation so far this morning continues to struggle thanks to dry air, and skies are slowly clearing in south central SD. Temps have remained fairly steady thanks to the cloud cover, in the upper 40s and lower 50s. Breezier winds expected across south central SD today with gusts around 30 mph.

Expect any showers to struggle through the rest of the morning and into the afternoon with the first piece of weaker PVA ahead of the main wave, which follows behind tonight through Friday. Today should be a mix of clouds and sun with highs still on the cooler side in the 60s. No significant changes to the forecast, although blended guidance is continuing to trend upward with rainfall amounts. Showers increase with the aforementioned wave and increasing mid level moisture late tonight through Friday. Still hints of weak, mainly elevated instability, so expect some rumbles of thunder but no severe weather through Friday night. Ensemble guidance also continues to trend up in expected rainfall amounts with chances for over half an inch remain 50 to 75% over most of our area, and a 20- 40% of 0.75" or more for areas between the James River and east to US Hwy 75.

DISCUSSION

Issued at 1257 PM CDT Wed May 20 2026

A weak wave and mid level moisture around the dgz moves in tonight, bringing a small threat for showers. Most locations will see a fairly stout dry layer below the incoming moisture which will severely limit rainfall potential. One exception may be west of the James River late this afternoon and early this evening when a little weak instability develops during peak heating which could support isolated showers there.

Lift and very weak instability moves in on Thursday ahead of the next wave. The chances for rainfall remains very limited with this. Otherwise expecting partly to mostly cloudy skies and highs in the 60s.

Thursday night into Friday will see warm advection and upper level support spread into the area. Most of Thursday night will see the better chances remain to the south of the Missouri River, but after midnight chances will increase. For the most part, showery and very isolated thunderstorms will be instability driven near and east of I- 29, while west of I-29 better upper level support for rainfall will be the driving factor. While the convective portion is of course a little less predictable, assuming some convective component does develop a few locations could see 1-2" of rain. Many of the latest models are each indicating swaths about 20-40 miles wide of 1-2" amounts. What also appears to be fairly consistent is that especially west of Highway 81 is where the most consistent suggestions for a more widespread quarter to three quarters of an inch of rain is possible.

Most of the lift will drift northeast on Saturday with a few sprinkles possible in the morning. Otherwise a mild day with highs most in the 60s to lower 70s.

Model soundings hinting at some weak, surface based instability on Sunday afternoon and evening which may allow for an isolated thunderstorm to develop. With some dry low levels and weak shear gusty winds would likely be the main threat if anything can develop. Confidence in this is low for now.

By Monday stronger southerly flow sets up an continues through the middle of the week. High temperatures in the 80s should be common. With upper level ridging in place Monday through Wednesday and very little upper level energy expected to move through the area mostly dry conditions are expected. Some hints of some support Wednesday into Thursday so will have to see if this comes to fruition.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 619 AM CDT Thu May 21 2026

VFR conditions continue through most of the period with mid and high clouds. Southeast winds increase this morning with gusts around 20-25 knots east of I-29. Gusts around 20 knots continue through the overnight into Friday morning. Showers and isolated storms move into the MO River Valley late tonight, lifting north early Friday morning. Showers bring MVFR conditions. Refined timing for KSUX and included -SHRA mention during this cycle at KHON and KFSD.

FSD WATCHES/WARNINGS/ADVISORIES

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