textproduct: Sioux Falls

KEY MESSAGES

- Showers and very isolated thunderstorms will move through the area today. The main concern will be brief heavy downpours, though flooding is not expected.

- The active weather pattern continues bringing a high chance (>60%) of additional rain later Friday into Saturday.

- Daytime temperatures remain below normal, but should climb closer to normal Saturday into Monday.

UPDATE

Issued at 309 AM CDT Thu Sep 24 2026

A trough of low pressure will slowly work east today with broad warm air advection in place ahead. With weak instability aloft and saturation within the dendritic growth zone, showers and very isolated thunderstorms are expected. The latest models are fairly consistent producing an area of a half an inch to an inch of rain, with the better chances over parts of southeast SD and northeast NE.

Drier air works in aloft west of I-29 this afternoon, but lower level saturation remains so cloudy conditions remain in place. With weak lift in this lower level saturation some patchy drizzle will be possible. Farther east over parts of northwest IA showers will likely continue through the night as this drying is slow to move in.

Any loss of rainfall will be short lived as the next wave moves into the area on Friday which will slowly exit on Saturday afternoon. The better chance for rainfall will be Friday night into Saturday morning. Another decent chance (30-50% chance) for a half an inch to an inch of rain is expected, but this time the better chances should be near and east of I-29. Severe weather and flooding chances remain very low.

DISCUSSION

Issued at 215 PM CDT Wed Sep 23 2026

Light rain showers located along and south of Highway 20 will continue to drift east and taper off by early to mid afternoon today. Highs will be in the mid 60s west of I-29 and in the low 70s to the east where clouds have cleared.

Looking aloft we have a low amplitude ridge centered over the northern Plains. To the west over the north central Rockies a weak jet streak is lifting a shortwave east-northeast. To the southwest over the Four Corners region a second shortwave begins to slowly move northeast. These waves will be the driving force behind a few rounds of slow moving showers and thunderstorms. Looking aloft to the east we see a Rex block over southern Ontario and down into the Ohio Valley. This block is responsible for the slow progression of storms over the next 24-48 hours. Looking at the mid-levels moderate Theta-e advection brings north warmer and moist air that pools over central Nebraska, South Dakota, and North Dakota, ahead of the first wave. By mid-afternoon the LLJ begins to increase as the wave arrives with a strong push of WAA. From the southwest a band of positive vorticity advects in, further increasing dynamic forcing. A band of showers and thunderstorms are expected to form along this juncture in central South Dakota late this afternoon. Severe weather is not anticipated, however there exists enough shallow instability that a few stronger thunderstorms may produce brief periods of heavy rain. This north/south band of storms will slowly progress east through the evening and overnight. Around Sunrise Thursday storms should be along and west of I-29, and ending over central South Dakota. Storms continue to slowly progress east through Minnesota and Iowa the remainder of the day Thursday with showers ending from west to east through the late afternoon and evening. Highs for Thursday will once again be cooler than average for this time of year, in the low 60s east of Highway 81, and upper 60s to low 70s west.

Through the course of the day Thursday, the Four Corners wave will move slowly northeast. By late Thursday evening into early Friday morning the Rex block that was slowing everything down will begin to break down. This will allow the wave to accelerate northeast through the overnight. With it will come a strong push of WAA and a strong band of vorticity advection. As dynamic forcing increases showers and thunderstorms will form along the leading edge of these elements. Storms move north and increase in areal coverage through the day Friday, becoming widespread. Once again severe weather is not anticipated, but some lightning and brief heavy rain are possible. Meanwhile, a strong trough will push into the Pacific Northwest through the day Friday. As it ejects out onto the northern Plains overnight into Saturday it will begin to push the existing storms to the east. The strong upper trough will keep pushing everything out of the region and storms will taper off from west to east early Saturday afternoon through the evening.

As far as rainfall totals are concerned, the GFS, EC, and CAN ensembles have fluctuated a bit but over all keep the main band of higher accumulation from roughly northeast Nebraska into southwest Minnesota. HiRes guidance has some shifts west or east to the heaviest band but for the most part they align with the ensembles. LREF probabilities from now until 7pm Saturday indicate a greater than 80% probability for widespread 0.25 inches of rain. Increasing totals narrow in a similar pattern to the model guidance of highest precipitation, with a 40-80% probability of 1 inch of total rain. Please note, isolated pockets of 1+ inches are also possible. Localized ponding is possible, as well as rises in creeks and streams, but river flooding is not expected at this time.

Saturday overnight will be dry and so will Sunday. By Sunday afternoon a few peaks of sunshine will be possible. Thanks to continuous southerly to southeasterly winds and WAA during this time, highs will gradually increase from Friday onward. Friday will see highs in the mid to upper 60s. Saturday and Sunday will see highs in the mid 60s to low 70s. Alas, our warmer and dry conditions will be short lived. Beginning Monday a series of waves brings more chances for rain and thunderstorms for the first half of the week. Highs will trend down from the mid 70s to the low 60s.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1257 PM CDT Thu Sep 24 2026

An area of rain extends from Marshall to Sioux Falls to Tyndall and points east to start the period. This area of rain will continue to slowly drift east through the afternoon hours and clear the area through the evening. However, MVFR to IFR conditions are expected for the majority of the area through the period, with some areas of LIFR cigs late tonight/early tomorrow morning as stratus continues to lower in spots. Along with this stratus, periods of drizzle are also expected especially during the morning hours tomorrow, reducing visibilities at times.

Additional rain showers will be possible mainly along the Highway 20 corridor late tonight into tomorrow morning, with perhaps a few pop-up showers towards I-90 by the end of the period. Thunder is unlikely. Winds will be mainly out of the south-southeast through tonight, with winds turning more southeasterly into the day tomorrow. Winds will gust to around 20 kts at times this afternoon, otherwise winds will be fairly light through the period, sustained around 5-10 kts.

FSD WATCHES/WARNINGS/ADVISORIES

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