Marine Weather and Tide Forecast for Yankton, SD

DISCUSSION
Issued at 1221 PM CDT Sat Jul 11 2026

THIS AFTERNOON: It's a hot day across the region with plenty of sunshine. High temperatures climbing into the 90s in most locations, but with dew points mixing down lower into the 60s, heat index values remain below critical values. That said, anyone spending time outdoors over the next days will need to take preventative actions from a very high UV index.

TONIGHT: Winds again turn light and variable through the night. The NBM has been biased a bit too cold with overnight lows the past days, but we will begin to see dew points lower a bit at night which could lead to some lows into the upper 60s. HRRR probabilities show less potential for fog this morning than last night, however, the favored areas would again be across NW Iowa for patchy morning fog.

SUNDAY: Pretty much an identical day on Sunday, with a bit more southwesterly wind fetch west of I-29. This will result in high temperature creeping a couple degrees warmest west of I-29. However with deeper mixing, dew point mix downwards further, and will again keep heat index values below critical thresholds.

MONDAY-FRIDAY: Really no major changes in the forecast for the upcoming work week. The mid-lvl ridge continues to build through the Northern Plains centering itself along the ND/SD border by Monday and then building southward and broadening by the middle of the week along I-90. The result will be daily highs in the 90s to even lower 100s in a few areas west of I-29. The daily direction of the surface winds will dictate some variance in warming, with southwesterly wind fetch allowing for deeper mixing and slightly higher afternoon highs. Records this week appear to be safe even if 100s are reached. Most records for the upcoming week range from 104-113 degrees stemming from some severe past drought years). Fortunately no extreme rises in dew points are expected, which will keep heat index values below 100 degrees in most areas. Will consider heat headlines for portions of the James River valley areas and westward by Monday where highs do begin to cross the 100 mark, but heat index values remain 1-3 degrees below criteria. ECE/GEFS probabilities continue to highlight the James River valley with a 60%+ probability of exceeding 100 through Tuesday, however as southwesterly winds expand eastward late in the week, those probabilities to expand into the I-29 corridor. A side note with all of the heat concerns this week. Daily RH values do fall near or below 20% west of the James River into the week with afternoon wind gusts approaching 25 mph. We may begin to see some increase in fire danger given the dry out of fine fuels.

SATURDAY-SUNDAY: We may begin to see some break in the ridge by next weekend, as a weak mid-lvl wave flows northward through the Plains and a second wave crosses near the Canadian border. While this could bring some clouds to next weekend, low-lvl moisture transport through the Central Plains veers off quickly east, and the Canadian wave is only bringing limited Pacific moisture with it.
Precipitation chances remain low at this point, with LREF guidance indicating no more than a 17% probability of >0.25" of precipitation through Monday morning.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 1152 AM CDT Sat Jul 11 2026

Outside of scattered CU this afternoon, VFR conditions are likely over the upcoming 24 hours. Fog risks appear lower for Sunday morning, but areas of NW Iowa will still need to monitor for any shallow development.

FSD WATCHES/WARNINGS/ADVISORIES
SD...None.
MN...None.
IA...None.
NE...None.