Tornadoes:

Tornado - 8 mi northeast of Herreid, SD Campbell County Date May 22, 2016 Time (Local) 6:30 - 6:35 pm CDT EF Rating EF-0 Est. Peak Winds 70 mph Path Length 0.25 miles Max Width 30 yards Injuries/Deaths 0/0 Summary: This brief landspout tornado touched down in an open field northeast of Herreid near the ND/SD border. Track Map Downloadable KMZ File

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Wind & Hail:

Storms that first developed during peak heating in the late afternoon possesed the largest threat for large hail. This took place across central South Dakota, and a couple reports of severe quarter sized hail (1 inch diameter) occurred in both Wakpala and Mound City. The image on the right is from Wakpala, courtesy of Laura Grijalva.

Hail

Spc Storm Reports

Wind

Once the initial storm cells across central South Dakota congealed and developed into a line later in the evening, the threat for hail decreased but the threat for strong winds increased. At 10:53 pm CDT, Pierre recorded a wind gust of 61 mph, and wind gusts in the mid 50 mph range continued as storms propogated east. For reference, severe thunderstorm criteria winds are 58 mph.

The most significant wind damage was reported in the city of Highmore late Sunday night. Structural damage was reported to the to the football field crows nest and bleachers. The strong winds also uprooted 40' pine trees at the courthouse and snapped branches off other trees. Finally, a liquid pump shed was blown down, damaging pipes and resulting in a 5000+ gallon chemical spill.

Damage to football field	Damage to football field	Uprooted trees	Uprooted trees

By the time storms reached the James River Valley area by around midnight, they had all but collapsed. However, a wind gust of 57 mph was recorded at the Aberdeen airport at 12:19 am early Monday morning. These winds were not produced by thunderstorms, but rather the low level jet - an area of strong southerly winds that typically develops above the surface during the night. In this case, these winds were brought down to the surface.

Radar Imagery focused on Pierre	Radar Imagery focused on Aberdeen

Photos & Video:

The Herreid Landspout - all photos and video courtesy of Josh Sayler

Landspouts are tornadoes, but different from the type that you'd normally think of. While typical tornadoes develop from rotating supercell thunderstorms and can last for an hour or more and produce EF-5 damage in extreme cases, landspouts develop when a thunderstorm updraft stretches and thus concentrates a relatively broad area of rotation. Think of a skater who begins to spin on ice with arms out, rotation is fairly slow, but as the skater pulls their arms in the speed of rotation increases. The same principle applies to landspouts (and waterspouts). Notice the radar image below - the storm responsible doesn't look very menacing, and no rotation was detected. This is why it's important to be in a safe place even during severe thunderstorm warnings. Landspouts are by nature are less of a threat than supercell tornadoes both in duration and intensity, but they are still very dangerous and fully capable of tearing a roof off of a home. 

Rain Reports

After a dry spell, many locations received beneficial rains of at least a quarter inch.