textproduct: Sioux Falls

KEY MESSAGES

- Isolated thunderstorms could develop this afternoon and evening. IF storms are able to develop, two+ inch hail and 50-70 mph winds are the main hazards. An isolated tornado is also possible.

- Warmer temperatures continue on Friday, with another low chance (20-30%) for thunderstorms in the afternoon and evening along and south of the Missouri River.

- Slightly cooler weather for the weekend. Saturday should remain dry with rain chances (40-70%) returning to portions of the area by Sunday morning.

- Additional chances for rain, and potentially thunderstorms (5- 10%), are possible through the first half of next week. Details are uncertain, so continue to check the latest forecast for the most up to date information.

DISCUSSION

Issued at 210 PM CDT Thu Aug 20 2026

A light shower or two persists across southwest Minnesota this afternoon. These showers remain ahead of a cold front that is just pushing into the forecast area. This front will serve as the focal point for potential severe storm development later this afternoon. The main shortwave is just north and east of the forecast area. However, the upper level jet will be nosing its exit region into the southwestern half of the forecast area. This presents a bit of a displacement in where the better shear and forcing will lie. Some capping remains across the area but the weakest amount of capping looks to be just along the front itself. Think that 1 to 4 storms is possible this afternoon and evening IF storms are able to develop. IF storms develop, more than sufficient instability will be in place with CAPE values up to 2,000 J/kg to 2,500 J/kg as moisture pools ahead of the front. With part of the upper level jet overhead, vertical shear will also be sufficient with deep layer shear values between 40 to 50 knots. DCAPE values will be highest along and just behind the front with magnitudes up to 1,200 J/kg. Thus, Large hail to 2+ inches and damaging winds to 50-70 mph will be the main hazards. A low 2% chance exists for a tornado as the low level jet begins to strengthen this evening, slightly expanding low level hodographs and increasing 0-3km storm relative helicity (SRH) values up to 100+ m2/s2. Any chance for severe storms for be waning through the evening hours as nocturnal stabilization increases capping. The previously mentioned cold front will stall out over the forecast area tonight, leaving muggy conditions in place. With light winds expected, patchy fog is once again possible.

Highs will remain in the 80s across the area on Friday. The previously mentioned cold front will push through the forecast area and end up right along the Missouri River. This could result in a few storms developing on this boundary before quickly pushing off to the south and east. However, latest LREF probabilities remain low (20-30%) for a tenth of an inch of rain or more. The HREF shows little to no probabilities for any precipitation. This is in line with the latest hi-res guidance as the bulk of this guidance shows storms developing south of the surface front in Nebraska. Will keep an eye on this potential in case storms trend back north, but for now, it looks most likely that the forecast area will remain dry tomorrow. Low temperatures will fall to the upper 50s and low 60s overnight.

Saturday will be a dry day as high pressure passes through the forecast area. High temperatures will be a little cooler, only warming to the upper 70s to low to mid 80s. The dry conditions will be brief as the next round of rain will return on Sunday as another shortwave trough will push into the Northern Plains. Latest ensembles show a 40-70% chance for rainfall totals to exceed a tenth of an inch through the day. Latest machine learning (ML) guidance keeps the highest chances for severe storms to the west of the forecast area. This may change over the next few days so will continue to monitor the potential for severe storms on Sunday.

High temperatures will remain near seasonable in the upper 70s and 80s for the first half of next week. Active zonal to northwest flow will persist aloft as well, contributing to additional risks for showers and storms. ML guidance does shows a small increase in potential severe storm risk, though the probabilities only 5 to 10%. Something to keep an eye on going forwards as weak shortwaves within the active flow can deliver additional chances for potential severe storms.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1226 PM CDT Thu Aug 20 2026

VFR conditions begin the TAF period. A few light showers persist across parts of southwest Minnesota but are on the move out. A cold front is just west of the forecast area but will push into the area through the first half of the afternoon timeframe. Showers and thunderstorms may develop along the front later this afternoon and evening. Confidence is high enough to include in KFSD's TAF at this time but trends in storm development will be monitored. Chances for storms will end late this evening, leaving light and variable winds for the overnight hours. Patchy fog is once again on the table though confidence is too low to include in a TAF at this time. Light northerly flow will finish out the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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