textproduct: Sioux Falls

KEY MESSAGES

- Morning showers and isolated storms continue, with increased risks for thunderstorms south of I-90 today between 2 pm and 10 pm. Isolated strong to severe storms possible, with large hail (up to 1.5") and strong wind gusts (60-70 mph).

- Thunderstorm risks continue tonight into Thursday morning, slowly shifting northward. Persistent marginal large hail risks along with the potential for locally heavy rainfall are expected. Exact locations remain uncertain, though favor areas along/north of I-90.

- More of the same Thursday into Thursday night with isolated to scattered severe storms possible in the afternoon and evening; exact area remains uncertain. Locally heavy rainfall risk continues.

- Temperatures rise through the upcoming weekend, bringing additional thunderstorm risks by Sunday and into next week. Monitor for strong storm potential.

DISCUSSION

Issued at 351 AM CDT Wed Jun 11 2025

TODAY: Showers and isolated thunderstorms continue this morning along and north of US Highway 14 stretching southwest into southwestern SD with a mid level wave approaching and near the nose of the LLJ. Surface boundary is slowly moving south this morning, evident on radar around 3 AM CDT stretching from roughly Plankinton to Viborg to Milford. This boundary should continue to move to the south through the morning hours, later becoming a catalyst for thunderstorm development this afternoon and evening.

Ahead of that though, expect these elevated showers and isolated storms to continue to move to the east this morning, with the greatest chances continuing to be around the US Hwy 14 corridor. Patchy areas of wildfire smoke may mix down to the surface through the day leading to locally reduced visibility and air quality. Moisture increases south of the boundary though the early afternoon hours, and with temperatures in this area into the upper 80s and lower 90s, should lead to a corridor of increased instability around or above 1500 J/kg (although the GFS/NAM are much greater in values) between the US Hwy 20 corridor and the I-90 corridor east of the James River Valley. Highest shear values (40+ kts) remain to the north of I-90 ergo offset from the best instability; however, shear values around 25 to 30 knots still support large hail and damaging wind gusts (especially with drier sub cloud layer). Tornado risk is very low; that said, should a storm be more surface based near the boundary, there may be enough 0-1 km shear to support a brief spin. The main threats with thunderstorms are hail up to the size of ping pong balls (1.5") and wind gusts to 70 mph between 2 and 10 PM. Locally heavy rainfall is possible. Storms should taper off late in the evening with the loss of instability.

TONIGHT: There may be a lull in shower and thunderstorm activity before development commences along the elevated (850mb) front/WAA wing and near the nose of the LLJ around 1 AM. This activity looks to be more along and north of I-90, possibly as far north as US Hwy 14. Not much in the way of instability (less than 1000 J/kg) with mid level lapse rates less than 6.5 deg C/km. Stronger storms could produce hail to quarter size. Locally heavy rainfall is more of a concern tonight than during today, as storm motion and development will be nearly parallel to the west-east oriented front. Lower level winds continuing to shift to the south allow for efficient moisture transport, and a deep warm cloud layer over 10k ft supports efficient rainfall rates. Isolated to scattered flash flooding may occur, especially in urban or low lying areas.

THURSDAY-THURSDAY NIGHT: Thursday's severe and heavy rain threats are going to be highly dependent on where boundaries end up after convection today through tonight. However, 11.00z guidance seems to be trending more northerly (toward US Hwy 14 or north) with the fronts and the mid level wave ejection, so trended the higher pops in that general direction. Less confident in the evolution of precipitation through the evening and into Thursday night with timing differences in frontal passages. Strong to severe storms are again possible, although confidence in timing and location is low. Hail to the size of ping pong balls and wind gusts to 70 mph would again be the main risks. Locally heavy rainfall is also possible, with more concern for areas which receive storms and heavy rainfall today and tonight. Areas north of I-90 and especially southwestern MN look to be at the greatest risk for heavier rainfall. Given the shift of the front north, raised highs a couple of degrees, especially south of I-90.

Rainfall amounts into early Friday will be highly dependent on storm coverage; however, pockets of 2-4 inches are possible with about a 30% chance north and east of Sioux Falls. Mean values across the area are generally 0.25" to 1.25".

FRIDAY-SATURDAY: Lingering showers and storms move east with the trough Friday. Mid and upper level ridging begins to build to the west with surface high pressure moving in as well. Could see some additional showers and isolated thunderstorms with a couple of ridge riding waves, but confidence is low on the details, especially with soundings showing a lack of moisture. Temperatures generally within 10 degrees of average.

SUNDAY ONWARD: Ridging slides east and flattens into the early part of next week, with at least one more ridge rider Sunday. A more defined mid/upper level trough develops early next week, sliding east near the International Border sometime late weekend into early next week. Models are quite varied on the details of this trough and associated surface low, but this could bring additional shower and storm chances to the region. Guidance continues to diverge mid to late next week, with the 11.00z GFS most bullish on a deep mid/upper level trough moving through the Plains. Although details are uncertain, this pattern is conducive to periods of showers and thunderstorms. Machine learning and other guidance indicates that some strong to severe storm potential exists, so stay tuned to the forecast for updates - especially if you have outdoor or travel plans Sunday into next week. Temperatures stay in the mid 70s to upper 80s for highs and mid 50s to mid 60s for lows.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1047 PM CDT Tue Jun 10 2025

VFR conditions begin the TAF period. A cold front continues to push southwards through the area late this evening. Winds ahead of the front remain out of the southwest while winds behind the front are out of the north. Weak showers have developed north of highway-14 which will persist through the overnight hours. A few hours of low level wind shear (LLWS) are expected along and south of I-90 as well.

Winds will turn easterly for the daylight hours tomorrow with gusts up to 15-25 knots expected. A second round of showers and thunderstorms is possible mainly east of the James River during the late morning and afternoon hours. Tough to say exactly where storms will initiate and track so did include PROB30 groups for -TSRA in KFSD and KSUX's TAFs. Some surface smoke is also possible throughout the day tomorrow as well. Chances for showers and storms will finish out the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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