textproduct: Sioux Falls

KEY MESSAGES

- Warm and mostly dry conditions are expected today. Increasing humidity may push heat indices near 100F in a few areas mainly west of I-29 this afternoon. - Chances for showers and storms increases late tonight through Thursday, continuing Thursday night into early Friday. Some storms may be strong to severe late Thursday into Thursday night with strong wind gusts and heavy rain the main threats.

- Beneficial rainfall is expected Thursday through Friday morning, with a 50-90% probability of at least 0.50 inches across most of the region.

UPDATE

Issued at 340 AM CDT Wed Jul 29 2026

Seeing some generally shallow fog develop in parts of the area as of 3 AM. Some signal that it may become a bit deeper in our east during the next 2-3 hours before sunrise with some fog becoming apparent on satellite, so have added mention of fog to the grids through 7-8 AM, mainly over portions of northwest IA and southwest MN.

Pre-sunset satellite also depicted a broad area of smoke aloft across the region so have bumped up sky cover from the mostly clear NBM forecast to account for potential of smoke limiting view of the stars overnight and filtering sunshine into the day Wednesday.

Unsure whether smoke will hamper warming significantly, but NBM continues to show a general warm bias with influence from the GEFS members, so conservatively nudged highs Wednesday down a degree or two. This combined with dew points in the upper 70s to mid 70s does yield heat indices marginal for Heat Advisory in some areas west of I-29, but given uncertainty in smoke impacts on warming, opted to hold off issuing any heat headlines at this time. Day shift will want to monitor for potential headlines generally along/west of the James River Valley (Huron-Yankton) and potentially as far east as Sioux City).

Evening shift thoroughly covered convective potential over the next couple of days, and not seeing any significant changes to that thinking in the latest data. That discussion in included below.

Issued at 907 PM CDT Tue Jul 28 2026

Wednesday looks to be somewhat of a rinse and repeat of what we saw today. A mid level ridge axis will be sitting right over the forecast area, contributing to weaker vertical shear values over the area. Instability looks to still be sufficient to allow for the potential of some afternoon showers and storms to develop. Tough to say where specifically storms may develop as no boundary will be in play. Should showers and storms develop, they look to be diurnally driven and will dissipate during the evening timeframe. Severe storms are not expected. The potential for overnight convection remains but it looks to be sub severe and won't make it into the forecast area until near daybreak early Thursday morning.

The overnight storms may have an affect on the potential for storms later on Thursday. With a surface high pushing further off to the east, allowing for moist southerly return flow to take over. This will allow dew points to moisten into the upper 60s and 70s. If the morning showers and dissipate fast enough to allow for sufficient destabilization to take place during the afternoon, then additional showers and storms will be possible. A mid level wave will be pushing through the forecast area with both deterministic and ensemble guidance suggesting that this mid level wave could close off as it moves over the forecast area. These models also show the surface front residing beneath the center of this mid level wave. This looks to potentially limit the strength of the deep layer shear. At the same time, mid level lapse rates also look to be near moist neutral. Precipitable water (PWAT) values look to climb to nearly 2.0 inches, placing them at about the 99th percentile of climatology. Thus, a heavy rain threat remains possible. Latest ensembles continue to show a broad 50-90% chance for rainfall amounts to exceed a half an inch. These probabilities decrease to a 30-60% chance for exceeding an inch. Tough to say exactly how convection will evolve, but with a generally uncapped atmosphere in play and the mid level wave providing at least wave forcing for ascent, think that more widespread convection could develop across the area. With the mid level wave residing right over the forecast area, storm motions do not look to be fast, suggesting that slow moving to potentially some training storms will be possible. Severe storms could be possible with this potential heavy rain threat if storms could develop on the previously mentioned front and possibly congeal into some kind of MCS. This potential remains uncertain so continue to check the latest forecast for the most up to date information.

DISCUSSION

Issued at 135 PM CDT Tue Jul 28 2026

A very subtle wave continues to move to the southeast. As it does so clouds will dissipate, gradually becoming scattered to clear. Similar to yesterday, smoke from wildfires will result in an overall milky appearance to the sky. Highs today will warm into the upper 80s to low 90s. Dew points will be lower than the past couple of days but still in the mid 60s to low 70s, highest over northwest Iowa. Localized higher values are possible in areas with large corn fields, as the plants add moisture through evapotranspiration. Heat Index values remain below critical today. However, it is still important to take care of yourself while working in hot conditions. Winds today will be southerly and light. Overnight they become light and variable. Patchy areas of fog are possible as overnight lows fall to the mid 60s and low 70s, which is right around the dew point temperature. Most of the fog should be contained to water ways and low areas, and will burn off by mid-morning Wednesday.

Northwest flow aloft continues for Wednesday, keeping the smokey skies in place. Wednesday during the day will be very similar to today with highs in the upper 80s and low 90s. Southerly winds increase in the afternoon as a shortwave approaches from the west. Gusts of 15-25 mph are expected with gusts increasing as you move toward central South Dakota. Showers and thunderstorms form in the late afternoon and evening over western South Dakota and progress east. Storms will reach central South Dakota and our western CWA border around midnight. There remains some variance in mid- range guidance on how this wave and resulting storms will evolve, therefore uncertainty in severity remains high. Model soundings show a dry subcloud layer and tall skinny CAPE. This indicates the most likely threats will be strong to marginally severe wind gusts and periodic heavy rainfall. A weak LLJ helps to maintain convection through much of the day Thursday.

Meanwhile, an upper level trough develops over the Pacific Northwest and speeds east. The mid-level and upper troughs deepen and a surface low forms over eastern Wyoming and western South Dakota. Similar to Wednesday night's storms, uncertainty in storm evolution is high due to wide variance in guidance. In addition, the activity and outflows from storms earlier in the day will likely play a role in evening development. The most likely scenario is a few isolated strong to severe supercells form over central South Dakota and quickly grow upscale into an MCS with damaging wind gusts and periodic heavy rain the primary threat. This tracks east through the overnight and early Friday morning, bringing beneficial rainfall to much of the area. LREF probabilities of 0.50 inches of rain or more are 55-75% region wide. This probability is for total rainfall from Wednesday night through Friday morning.

Thursday will be cooler due to clouds and rain with highs in the low to mid 80s. Friday continued CAA will result in highs slightly cooler in the upper 70s to low 80s. A beautiful weekend is in store with mostly sunny skies and highs right around average for this time year in the mid 80s.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1244 PM CDT Wed Jul 29 2026

Can't rule out a pop-up shower or thunderstorm this afternoon and early evening along and south of a KSUX to K9V9 line; however, chances for this are quite low, generally less than 20%. Otherwise, additional showers and storms can be expected heading into the day tomorrow. Lower confidence in coverage of morning thunderstorm activity Thursday precludes mention of TSRA in the TAFs at this time, as the better chances appear to be after the current forecast period.

Winds will be mainly out of the southeast through the period, gusting to around 20 kts at times this afternoon near and west of the James River and again during the daytime Thursday across the area.

FSD WATCHES/WARNINGS/ADVISORIES

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