textproduct: Sioux Falls

KEY MESSAGES

- Isolated thunderstorms will be possible mostly across portion of southcentral SD this morning. While these storm will likely stay sub- severe, smaller hail will be possible.

- A linear Mesoscale Convective System (MCS) will likely develop over central SD by Wednesday night and progresses into portions of southeastern SD. The primary hazards will be damaging winds up to 65 mph and large hail up to half dollar size.

- Additional chances for showers and storms will continue into the late week with the focus being between Thursday and Friday. Mixed storm modes could bring a variety of severe weather risk, but slower storm motions may also bring a locally heavy rain risk.

DISCUSSION

Issued at 348 AM CDT Wed Jul 9 2025

TODAY & TONIGHT: Taking a look across the area, mostly quiet conditions continue as of 4 am this morning. The forecast still remains on track for a few isolated thunderstorms developing across southcentral SD through daybreak as pieces of vorticity interact with a 20-30 kt LLJ. However, the severe risk with this activity will likely stay on the lower side with only around 500-750 J/kg of instability to work with. As the LLJ weakens, should see this activity weaken and diminish by mid-morning. Shifting gears here, another warm day is ahead as increasing southeasterly winds and increasing mid-level warm air advection (WAA) lead to temperatures in the 80s to low 90s with the warmest conditions closest to the warm front situated along and west of the Missouri River Valley. From here, the focus turns to our next precipitation chances this evening and overnight.

Taking a look aloft, a quick mid-level wave will push across the state and intersects the previously mentioned warm front triggering semi-discrete clusters of showers and thunderstorms across western and central SD. While this developing activity will have access to an unstable environment characterized by 2000-3000 J/kg of instability and 25-35 kts of bulk shear, model soundings continues show a stabilizing boundary layer as this developing activity moves into our CWA. As a result, most high-resolution guidance has this developing Mesoscale Convective System (MCS) weakening as it progresses eastwards towards the I-29 corridor. With this in mind, the majority of the severe risk (if any) will likely be isolated to areas west of U.S. Highway-281 where remnant thunderstorms could produce damaging winds up to 65 mph and half dollar sized hail. Lastly, as the LLJ strengthens across areas east of I-29 overnight; some potential redevelopment will be possible mainly in northwestern IA. While this activity will likely be sub-severe due to waning instability, can't completely rule out the potential for a few additional thunderstorms with some smaller hail.

THURSDAY-FRIDAY: Looking into the latter parts of the week, could see the previously mentioned activity lingering across areas east of I-29 through the mid-morning hours on Thursday before things progress out of our area. From here, quieter conditions temporarily return through the late afternoon as temperatures peak in the 80s to low 90s for the day. More shower and thunderstorm chances will return during the evening to overnight hours on Thursday as a strengthening shortwave lifts through our area and intersects a few lingering surface boundaries left behind from the previously mentioned MCS. While there is still some uncertainty regarding where things will set up, the high CAPE/low shear environment associated with this system; will likely support an isolated to scattered severe risk with stronger storms potentially develop up to 2 inch hail (Hen Egg) and damaging winds up to 70 mph with strong cold pools. As instability wanes overnight, slower storm motions along with PWATs between 1.50 to 1.75 inches (90th percentile) will promote a locally heavy rainfall risk into Friday morning. Nonetheless, with the variety of convective scenarios its still a bit difficult to pin point an area of focus for the overall severe risk and antecedent heavy rainfall threats at this time. Lastly, given the increasing precipitation chances; expect temperatures to decrease from the 80s and low 90s on Thursday to the 70s to low 80s by Friday.

SATURDAY ONWARDS: Heading into the extended period, quieter conditions return to the area as surface ridging moves in by Saturday to replace the departing system. With backing surface wind profiles and increasing warm air advection (WAA) in the mid-levels, expect temperatures to trend near to above normal over the next few days with highs increase from the upper 70s to mid 80s by Saturday to the mid 80s to low 90s by Monday. From here, our next shower and thunderstorm chances likely return by Tuesday as a cold front swings through the region. While the severity of this activity is still uncertain, some of the machine learning guidance has started to show some weak signals for stronger activity so this period will likely be one to watch moving forwards.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 950 PM CDT Tue Jul 8 2025

Isolated showers/thunderstorms will be possible through central SD into the James River Valley late tonight into Wednesday morning. Although this activity could approach KHON and KSUX, at this time guidance would suggest that this activity will remain west of the TAF sites. Any showers/storms would end by mid morning on Wednesday. Additional showers and thunderstorms may develop through central SD on Wednesday evening, and this activity could affect KHON toward the end of the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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