Storms moved over portions of northeast South Dakota that had really no extra room for moisture from the preceding months of nearly constant rainfall. Thus, this moisture went straight into the Big Sioux and tributaries from the Watertown area down south to Castlewood.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS ABR wrote it up.
Storms moved over portions of northeast South Dakota that had really no extra room for moisture from the preceding months of nearly constant rainfall. Thus, this moisture went straight into the Big Sioux and tributaries from the Watertown area down south to Castlewood. The COOP observer in Rauville would record 1.51 inches of rainfall pushing their monthly total up to 5.73 and a 3 month total of 23.32. The Watertown COOP would likewise come up with 1.86 inches, putting the monthly total at 5.85 and 20.1 for the preceding 3 months. Even Castlewood, while only topping out at 0.31 inches, would see their monthly total top out at 4.99 inches with a 3 month total of 22 inches.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Aberdeen, SD wrote its last area forecast discussion before the first event at Aug 21, 7:23 PM CST, 2 hours 37 minutes earlier.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Service Notice</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<main class="wrap">
<section class="card" role="status" aria-live="polite">
<div class="status" id="status">Temporary Notice</div>
<h1 id="headline">This service is currently unavailable.</h1>
<p id="message1">
The site you requested is temporarily down for maintenance or an unexpected outage.
</p>
<p id="message2">
Please try again in a few minutes.
</p>
<p class="small" id="detail">
If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
</p>
</section>
</main>
<script src="index.js"></script>
</body>
</html>Hazardous Weather Outlook National Weather Service Aberdeen SD 144 PM CDT Thu Aug 21 2025 MNZ039-046-SDZ005>008-010-011-016>023-033>037-045-048-051-221845- Traverse-Big Stone-McPherson-Brown-Marshall-Roberts-Edmunds-Day- Potter-Faulk-Spink-Clark-Codington-Grant-Hamlin-Deuel-Stanley-Sully- Hughes-Hyde-Hand-Jones-Lyman-Buffalo- 144 PM CDT Thu Aug 21 2025 /1244 PM MDT Thu Aug 21 2025/ This Hazardous Weather Outlook is for west central Minnesota, central South Dakota, north central South Dakota and northeast South Dakota. .DAY ONE...This afternoon and tonight. Late afternoon and evening thunderstorms come with a slight (2 out of 5) risk, mainly for large hail and damaging winds. We also cant rule out an isolated tornado up in far northeast South Dakota and western Minnesota either. Another round of storms is possible as the boundary shifts south overnight mainly along and south of highway 212 with a continuation of a large hail/high wind risk. A third round of storms is then expected to come in from the west during the early morning hours Friday. Overall a marginal (1 out of 5) risk of severe weather with this round. With the potential for multiple rounds of storms, heavy rain and flooding is not out of the question, especially in areas hard hit and saturated from this summers rains. The primary focus area of concern is along and south of highway 212 in eastern South Dakota. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation may be requested. Weather spotters are encouraged to submit reports to the National Weather Service in Aberdeen. The public can submit reports on our web page, Facebook page, or our X feed. SDZ003-004-009-015-221845- Corson-Campbell-Walworth-Dewey- 144 PM CDT Thu Aug 21 2025 /1244 PM MDT Thu Aug 21 2025/ This Hazardous Weather Outlook is for north central South Dakota. .DAY ONE...This afternoon and tonight. Showers and weak storms will pass through north central South Dakota during the afternoon and a second round early Friday morning. Aside from lightning, the risk for severe weather is low. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. 07
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Service Notice</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<main class="wrap">
<section class="card" role="status" aria-live="polite">
<div class="status" id="status">Temporary Notice</div>
<h1 id="headline">This service is currently unavailable.</h1>
<p id="message1">
The site you requested is temporarily down for maintenance or an unexpected outage.
</p>
<p id="message2">
Please try again in a few minutes.
</p>
<p class="small" id="detail">
If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
</p>
</section>
</main>
<script src="index.js"></script>
</body>
</html><!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Service Notice</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<main class="wrap">
<section class="card" role="status" aria-live="polite">
<div class="status" id="status">Temporary Notice</div>
<h1 id="headline">This service is currently unavailable.</h1>
<p id="message1">
The site you requested is temporarily down for maintenance or an unexpected outage.
</p>
<p id="message2">
Please try again in a few minutes.
</p>
<p class="small" id="detail">
If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
</p>
</section>
</main>
<script src="index.js"></script>
</body>
</html><!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Service Notice</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<main class="wrap">
<section class="card" role="status" aria-live="polite">
<div class="status" id="status">Temporary Notice</div>
<h1 id="headline">This service is currently unavailable.</h1>
<p id="message1">
The site you requested is temporarily down for maintenance or an unexpected outage.
</p>
<p id="message2">
Please try again in a few minutes.
</p>
<p class="small" id="detail">
If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
</p>
</section>
</main>
<script src="index.js"></script>
</body>
</html>Preliminary Local Storm Report
National Weather Service Aberdeen SD
1015 PM CDT Thu Aug 21 2025
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1010 PM Flood 1 WNW Watertown 44.91N 97.12W
08/21/2025 Codington SD Trained Spotter
Reports of street flooding in Watertown.
&&
SDPreliminary Local Storm Report
National Weather Service Aberdeen SD
1021 PM CDT Thu Aug 21 2025
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1018 PM Flood 1 ESE Watertown 44.90N 97.09W
08/21/2025 Codington SD Public
Report of additional street flooding in
Watertown.
&&
SDSpecial Weather Statement
National Weather Service Aberdeen SD
1040 PM CDT Thu Aug 21 2025
SDZ020-022-023-220415-
Hamlin SD-Deuel SD-Codington SD-
1040 PM CDT Thu Aug 21 2025
...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN DEUEL...
NORTHEASTERN HAMLIN AND SOUTHEASTERN CODINGTON COUNTIES THROUGH 1115
PM CDT...
At 1039 PM CDT, Doppler radar was tracking a strong thunderstorm near
Castlewood, moving southeast at 15 mph.
HAZARD...Wind gusts up to 40 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Clear Lake, Castlewood, Claremont Colony, Bemis, and Poinsett Colony.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4454 9681 4454 9683 4480 9711 4490 9698
4474 9658
TIME...MOT...LOC 0339Z 308DEG 13KT 4480 9698
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
10The national radar mosaic for the moment the first event began.
6 flood. Local standard time, as filed.
Willow Creek near Watertown went into flood on the evening of August 21st, topping out at 12.86 feet, or 2.86 feet above flood stage during the early morning hours of August 22nd before slowly falling, dropping below flood stage at 1230 AM August 23rd.
The South Branch Tributary Mud Creek near Rauville went into flood during the early morning hours of August 22nd, cresting at 4.91 feet, 0.91 feet above flood stage around mid-day. The creek would remain in flood through the early afternoon of August 23rd.
The Big Sioux near Castlewood would go into flood on August 22nd during the morning hours, cresting at 11.42 or 2.42 feet above flood stage on the morning of August 24th. The river would remain in flood through the evening of August 27th.
The Big Sioux River below Watertown river gauge would exceed flood stage starting in the morning of August 22nd, peaking at 11.68 or 0.68 feet above flood stage. The river crested in the evening and was back below flood stage by the late morning of August 23rd.
The Big Sioux River at Watertown Broadway Avenue stream gauge would report flooding during the late morning of August 22nd, peaking on the evening of the 22nd at 10.90 or 0.90 feet above flood stage. The river would remain in flood at this section through the early morning of August 24th.
The Big Sioux River at Watertown Sioux Conifer Road gauge briefly hit flood stage for a few hours on the morning of August 23rd.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2025Every state in 2025This day in weather historyWarnings in South Dakota, August 2025
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-10-01. Each event’s entry at NCEI: 1291979, 1291975, 1291976, 1291981, 1291982, 1291980.