textproduct: Sioux Falls

KEY MESSAGES

- Isolated to scattered thunderstorms should develop late this afternoon into early evening. Large hail up to half dollarand damaging winds to 60 mph would be the main hazards. A Level 1 of 5 risk for severe storms covers most of the area for this threat.

- Similar to today, a conditional Level 1 of 5 risk for severe storms covers the forecast area Monday afternoon. The chance of development looks lower than today, but if a storm can form, large hail and isolated damaging winds could occur.

- High chances (50-80%) for rain will persist through the bulk of next week. However, severe storm chances continue to look low (near 5% or less) through next week. The better chances for rainfall appear to be Wednesday in central SD and Wednesday night into Thursday area wide.

DISCUSSION

Issued at 1235 PM CDT Sun May 31 2026

An active pattern is expected over the next several days, although severe weather appears to remain a minor threat. Patchy heavy rain may play the bigger role with each event.

For this afternoon and tonight, a small corridor of low level convergence and lift will focus near and just east of the James Valley. Clouds have cleared through early afternoon and temperatures have risen a touch. Along with this temperature rise is a turn in the surface winds to a more south to southwest direction vs. southeast. This is what is aiding in this low level convergence. The latest model soundings indicate something around 1500-2000 J/kg CAPE but weak, disorganized shear. This suggests severe weather should remain limited, but maybe a cell merger or two could produce a couple of updrafts strong enough to support hail to half dollar and wind gusts to 60 mph. Stronger storms will likely drift east or northeast at about 15 mph, so fairly slow moving. With this slower storm motion in mind, will need to keep an eye on the locally heavy rain potential. A handful of the latest hi-res models are showing small areas of 1-3" of rain with this development. One area to keep a closer eye on will be parts of Western Lake county, Northeast McCook and western Minnehaha where 1-3" of rain fell late last night.

The question becomes what will drive development; will it be diurnal heating, which would allow updrafts to start developing around 19- 21z, or will it be the weak wave which moves into the area closer to 0-3z this evening. The latest HRRR and Nam output agree with the later start times, with the Nam indicating a stronger cap and less development, while the RRFS and RAP kick off development a little sooner with weaker capping. With the clearing that we are seeing in central SD towards the James Valley we may see some development by mid to late afternoon as destabilization is more likely. Suspect some development between about 5-6pm.

One last thing to watch out for, if we can get mid to late afternoon development, the LFC are marginally low and a weak convergent boundary should be in parts of south central and southeast SD, so an isolated funnel or two will be possible.

While a marginal risk for severe weather is in place for Monday, confidence in the chances of development are very low. A capping inversion may win out and for now CAPE values only running around 1000 J/kg with continued weak shear, albeit a little bit better than today.

Another wave moves through Tuesday but weak shear and weak instability suggest if anything can develop severe weather is very unlikely.

Wednesday into Thursday looks like the better chance for more clouds and better rainfall chances. Broad southerly warm advection looks to bring in some weak elevated instability as low pressure tracks east through ND. For now not anticipating all day rainfall but should see off and on chances Wednesday and Thursday as this low tracks by to the north.

Friday into Sunday will see periodic weaker waves move through the area with a continuation of relatively weak flow aloft. This continued weaker shear environment should keep severe weather threats very limited.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1214 PM CDT Sun May 31 2026

Clouds continue to clear from southwest to northeast. An area of stratiform rainfall will drift northeast through southwest MN and northwest IA through mid afternoon. Patchy MVFR conditions will be possible. Otherwise scattered thunderstorms will become possible from about the James River to I-29 late afternoon through early evening, then drift into parts of southwest MN and northwest IA late evening and early overnight. A few of these storms could be strong to very locally severe with locally heavy rain likely with the stronger storms. IFR stratus and possibly fog will fill back in late tonight into Monday morning. No mention of fog for now as the stratus development will likely offset this development. Regardless of fog or stratus, an increased threat for IFR conditions.

FSD WATCHES/WARNINGS/ADVISORIES

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