Marine Weather and Tide Forecast for Yankton, SD

DISCUSSION
Issued at 217 PM CDT Sun Jun 15 2025

A fast moving MCV appears to have driven less unstable air into southeast SD, and this air continues to push eastward into southwest MN and northwest IA. This may limit thunderstorm production this afternoon to area mainly near and east of the Buffalo Ridge south towards Ida Grove. With CAPE values around 2000 J/kg and weak shear, locally heavy rain will be the main threat. An isolated stronger updraft could produce hail to 1.25" to 1.75" and gusts to 60 mph.
This threat would mainly be late afternoon into the early evening.

Upper level energy will work onto the High Plains tonight and could bring some convective activity into central SD later tonight into the overnight hours. The better chance will be with the stronger wave that moves into northern SD late tonight and could drag a broken line of thunderstorms into areas north of I-90 and likely near and north of Highway 14. A low chance for severe storms with quarter sized hail and wind gusts to 60 mph.

On Monday this wave cruises through ND into Northern MN and should drop a weak front into the area through the day. By late afternoon this front will likely be near a Windom to Tyndall line and could spark a few thunderstorms. The latest model guidance is indicating a bit stronger cap and a bit less instability, albeit still pretty potent at 2500 to 3000 J/kg. For now the better chance for afternoon development appears to be in southwest MN closer to the exiting wave. If storms can develop golf ball sized hail and wind gusts to 70 mph will be possible.

By Monday night the main wave to the north will be well to the northeast and a weaker wave will move out of Colorado into Nebraska.
With the exiting wave likely leaving behind a low to mid level boundary, then incoming weaker wave be ignite development along this boundary, with the3 better chances near and south of I-90 Monday night into Tuesday morning. While shear continues to be on the weaker side, CAPE values of 1500-2000 J/kg should provide plenty of energy to any storms that develop. With a potential west-east boundary and storm motion likely in an easterly direction, heavy rain will be a threat. A few locations in far southeast SD and northwest IA have recently seen 2-5" of rain and will provide some potential for localized flash flooding. Still a lot to work out however between now and then so confidence on the low to moderate side for the severe/flash flooding potential.

This wave moves east on Tuesday and shoves the deeper instability to the south. However broad troughiness remains in place through Wednesday so scattered showers and thunderstorms remain possible with a lower threat for severe.

Thursday into next weekend will see northwest flow aloft give way to a fairly strong ridge. However, some strong southwest flow aloft just west of the area by Friday into the weekend could bring a few surprises and more active weather next weekend if this flow shifts a bit farther to the east. This will be something to watch. Otherwise, looking like a fairly hot period Friday into the weekend with highs in the 90s becoming likely.


AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
Issued at 600 PM CDT Sun Jun 15 2025

Showers and thunderstorms will continue east of Interstate 29 into the late evening. Chances will then be low for thunderstorm activity overnight, though some guidance would suggest additional development over southwestern MN and northwestern IA late tonight. On Monday, additional thunderstorms may occur in the afternoon and evening, though confidence in timing and location is low. Southerly winds will become gusty on Monday afternoon.

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