textproduct: Sioux Falls

KEY MESSAGES

- Numerous showers with embedded thunderstorms develop Sunday afternoon. Brief pockets of moderate rain are possible into the Monday morning, though storm motion limits flooding potential.

- A stronger storm or two may develop Sunday evening into the early overnight hours south of I-90. Hail to quarter size would be the primary risk, but isolated wind gusts to 60 mph are possible near Highway 20. Risk continues Monday east of a line from Ida Grove to Windom.

- After rain ends Monday afternoon, an extended period of cooler than normal temperatures continues through the week with only minor rain chances late Wednesday.

UPDATE

Issued at 331 AM CDT Sun Apr 26 2026

Temperatures remain in the upper 30s to mid 40s this morning, with isolated showers and drizzle. Although some hi-res guidance hints at fog west of I-29, winds are already increasing and cloud cover should prevent development so will continue to keep mention out of the forecast.

Forecast remains on track for the rest of the day, with increasing WAA and the approach of the mid level wave. Isolated rumbles of thunder are expected. No significant change to the Day 1 SPC Outlook, with a Marginal (level 1 of 5) risk for areas east of the James River and south of I-90 through the US Hwy 20 corridor. If stronger storms are able to develop, quarter sized hail is the main threat with any elevated storms. Any stronger surface based storms near US Hwy 20 may be capable of 60 mph wind gusts. Isolated severe threat exists from roughly 7 PM to 2 AM, with some CAMs showing a couple rounds of storms.

For Monday, SPC has introduced a Marginal (level 1 of 5) risk for severe storms for our far eastern tier of counties (east of a line from Ida Grove to Windom). Window for any severe weather looks limited as most guidance has the cold front pushing east of our area by mid afternoon. This leads to very low confidence in coverage and severe potential due to limited instability. If a stronger storm can develop, quarter sized hail and wind gusts to 60 mph are possible.

Locally moderate to heavy rainfall is possible into Monday, as the aforementioned tall and skinny CAPE profiles are supportive of more efficient rainfall rates. PWATs today through Monday are expected to be around or above an inch. However, 1 hourly FFG between 1.5 to 2+ inches for most of the area, antecedent conditions, and progressive storm motion should limit any flash flood potential. Would not be surprised, though, to see localized ponding with rainfall rates at times up to half an inch per hour.

DISCUSSION

Issued at 1219 PM CDT Sat Apr 25 2026

THIS AFTERNOON: Mid-lvl vorticity tracking through central NE will continue to produce areas of light rain into the evening. Generally rainfall totals have been running well short of CAM guidance this morning, suggesting greater impact from linger dry air. As the wave slowly slides east, we'll continue to see forcing near both areas of 850 and 600mb frontogenesis. Absent any meaningful instability, rainfall rates will remain quite. One item of note: We have received a couple reports of sleet on the western side of the precipitation area this afternoon. This process should diminish as strong warm advection increases.

TONIGHT: After a light uptick in echos in NW Iowa early this evening, the initial wave of vorticity will move east after dark. In it's wake, a very weak low-lvl warm advection regime will stay in place. The persistence of this weak lift may allow sprinkles to isolated showers to linger into Sunday morning, but QPF amounts will again be very light.

SUNDAY-SUNDAY NIGHT: Broad and weak warm advection persists Sunday morning again allowing the development (or redevelopment) and northward propagation of sprinkles to very light showers through the Tri- State area. By the afternoon we'll begin to see a shift in the mid-lvl flow as troughing begins to eject out of the Central Rockies. The advection of weak to modest elevated instability along with both the increasing low-lvl convergence and nose of the upper lvl jet energy should allow for numerous showers and thunderstorms to form over Nebraska early in the afternoon. The increase and slight veering of the LLJ should push this activity northward into the Tri-state area in the evening. Rainfall rates based on HREF guidance may range anywhere from 0.10" to as much 0.75" per hour, but with the fast northeast progression of rain any flash flood risk should be minimal.

One hazard to monitor will be the progression and northward extent of mostly elevated instability lifting northward Sunday evening. Latest guidance would suggest the northward advection of mostly elevated MUCAPE of 400-800 J/KG south of I-90. Soundings suggest this is a tall but thin CAPE profile, and while overall shear/wind profile isn't all that strong, CAMS are suggesting potential for a few bowing segments with small hail mostly near the Highway 20 corridor.

MONDAY: Upper troughing ejects into the Plains early on Monday, keeping rain chances high throughout the daytime hours. Greatest focus for isolated thunder will be through the morning hours before mid-lvl dry air arrives. Further west, the deepening upper trough would suggest a deformation band develops west of the James River early and then drags itself eastward into the early evening. With temperatures stuck in the 40s, a rather raw and windy day may be expected.

TOTAL QPF POTENTIAL: This system remains one that should bring some relief to what's been a very dry Spring season. The latest HREF 25/75th percentile guidance suggests that by 7am Monday most should see between 0.75" and 2". By the time the deformation band tracks through, some model guidance suggesting localized 2.5-3" totals may not be far off. Of course, the track of convection Sunday evening will determine the final totals.

TUESDAY-FRIDAY: Confidence remains quite high that the rest of this week will be cooler than normal. Deepening low pressure over the eastern third of the CONUS will keep a persistent northwesterly low- lvl flow in the region. The resulting high temperatures will climb into the upper 50s to a few 60s, just a shade below normal. The only meaningful risk for additional rain this week will present itself on Wednesday night into Thursday as a subtle wave passes through the NW flow. At this time, with no instability, any amounts will be very low.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1242 AM CDT Sun Apr 26 2026

Isolated light showers are moving through the area to start the period, but coverage is not great enough to include in any of the TAFs for the rest of the overnight hours. Light patchy fog can't be entirely ruled out this morning in central South Dakota as winds remain light with ample moisture, but the cloud cover out there will help keep this potential low (<20%).

Coverage of rainfall will increase especially from late morning onwards, bringing MVFR to IFR ceilings along with it. Activity will generally be lifting from southwest to northeast through the day today into this evening. A few thunderstorms will be possible mainly south of I-90 late Sunday afternoon into Sunday night, but confidence was only high enough to include a PROB30 group for -TSRA at KSUX at this time.

Winds will generally be out of the northeast this morning, with winds turning more easterly for most of the area heading into the afternoon, but turning southeasterly over portions of northwest Iowa. Winds will increase from the late morning into the afternoon and evening, with gusts up to 25 kts possible.

FSD WATCHES/WARNINGS/ADVISORIES

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