textproduct: Sioux Falls

KEY MESSAGES

- An extended stretch of hot temperatures will continue through the next week. Highs in the 90s may approach 100 degrees in a few locations. The cumulative nature of the heat could lead to some heat health concerns.

- Patchy morning fog will be possible each day, but widespread dense fog isn't likely.

- Minimal precipitation is expected over the next 7+ days, with the LREF probability of >0.25" through Tuesday July 21st only at 25%.

DISCUSSION

Issued at 1250 PM CDT Sun Jul 12 2026

THIS AFTERNOON: Another hot day across the region, though gusty winds are a bit slow to develop today. This may ultimately result in slightly lower temperatures, but could keep humidity a bit higher along and east of I-29. That said, heat index readings peak in the lower to middle 90s.

TONIGHT: Much like the past days, winds weaken overnight, but still stay mixy. This will hold overnight low into the upper 60s to lower 70s. It may also prevent any widespread fog development outside of very sheltered valleys.

MONDAY-TUESDAY: Low-lvl temperatures really do not change all that much for Monday, and this should result in a temperature forecast very similar to Sunday. By the late morning we may begin to see some stronger southwest gusts form along a line from Lake Andes to Brookings, however through the afternoon those winds may shift a bit more to the south and southeast. What will be apparent however is the lowering of afternoon dewpoints which may mix into the middle to upper 50s west of I-29 and middle 60s east of I-29. resultant heat index numbers peak in the lower to middle 90s in most areas, warmest west of the James River. WBGT remain at the moderate levels throughout the CWA. By Tuesday, there is some evidence that 850 mb temperatures may cool slightly as southeasterly winds at the surface and aloft pull weak cold advection northward. This is partially why recent CONSshort and NBM guidance has cooled high temperatures slightly on Tuesday. With dew points at peak heating ranging from the mid 50s to the lower 60s, heat index values again only top into the middle 90s in the western CWA. WBGT values do creep up slightly, but the vast majority of the CWA remains at moderate levels. Given the current heat index values remaining a few degrees below 100, WBGT only in the moderate range, and a 25+ drop in overnight temperatures from afternoon highs, not anticipating a heat advisory at this time. However, continue to use extra precaution if spending time outdoors.

WEDNESDAY-FRIDAY: We'll certainly begin to see the hottest temperatures shift south and east through the end of the work week. 850mb temperatures remain close to Tuesday's levels around 20-22C, but we'll also see a bit more of a surface wind shift to the south. Compounding this with dry ground, and continued warmth of soil temperatures, temperatures will reach for the 100s along and west of the James River and into the lower 90s further east. The heat dome spreads east for Thursday and Friday, pushing 850C air between 24- 28C into the Tri-State area. This leads to increasing risks for middle 90s over MN/IA, with 100s spreading towards the I-29 corridor. The persistent mix-down of dry air each afternoon may keep HI from reaching extreme levels, but will likely begin to reach HI criteria Wednesday with these conditions spreading southeast through Friday. Advisories will most certainly be possible in this time frame as WBGT also jumps towards the high categories and "major" heat risk designations shift south as well.

SATURDAY-SUNDAY: Recent model trends continue to slow the gradual pattern evolution during the upcoming weekend. The slow approach of a SW-NE oriented boundary may only serve to help focus deeper mixing in the afternoon. This will leave most of the Tri-State area well under the thermal ridge on Saturday, with increasing potential for widespread upper 90s to lower 100 highs. The latest NBM still maintains a 12 degree spread in the 25/75th forecast, with those 75th percentile values all near or over 100 in the CWA. Heat index values are again below 100 in most areas with RH values in the 20- 30% range. A trough sinking into the Northern Plains Sunday could lead to the potential for isolated to scattered thunderstorms into Sunday, though lack of deep moisture may limit this risk. Highs do appear to lower slightly Sunday afternoon.

Precipitation amounts over the upcoming 7-10 days will not be significant in the area. 12Z LREF data continues to hint at very little rainfall ahead. The potential of >0.25" through Tuesday July 21st is only at 25%.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1136 AM CDT Sun Jul 12 2026

Outside of some scattered diurnal CU this afternoon, clear skies will prevail into Monday morning. As we've seen the past days, very patchy shallow fog could again be possible for 1-2 hours Monday morning. A few wind gusts are expected along and west of I-29 into the evening, with winds weakening overnight.

FSD WATCHES/WARNINGS/ADVISORIES

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