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The image on the left is a MODIS Aqua satellite image from early in the outbreak as storms began to erupt across parts of North Dakota and Minnesota. The image in the middle is a map of hail swaths from the National Severe Storms Laboratory. It is based on a computer algorithm that detects what the largest likely hail size is in a given thunderstorm, and then accumulates those hail predictions over time.

The image on the right is also from NSSL, and it depicts rotation tracks between 11am CDT on June 17th and 10pm CDT. This was generated by another computer algorithm which detects the strength of the rotation in a thunderstorm and then accumulates the areas of strongest rotation over time. The yellow and red colors indicate the strongest rotation. You can download a KMZ file of the rotation tracks to open in Google Earth (1.6MB) by clicking here.

Here are some regional satellite loops from Scott Bachmeier at SSEC / CIMSS in Madison, Wisconsin. These are large files, so the download may take some time.

Satellite Animations / Loops
GIF: Visible Infrared Water Vapor
QuickTime: Visible Infrared Water Vapor

Here is a collection of archived SPC Mesoanalysis graphics from June 17th. The mesoanalysis graphics are essentially a computer analysis of weather conditions at a given hour. This collection includes maps of instability and shear parameters, standard weather maps at different levels of the atmosphere, and more.

1 PM CDT Mesoanalysis Graphics
Sig Tor Parameter
Effective Shear
Effective SRH
MLCAPE
850mb Analysis 500mb Analysis Surface Temp/Dewpoint Visible Satellite
0-1km EHI 0-1km Shear LCL SBCAPE
 
3 PM CDT Mesoanalysis Graphics
Sig Tor Parameter
Effective Shear
Effective SRH
MLCAPE
850mb Analysis 500mb Analysis Surface Temp/Dewpoint Visible Satellite
0-1km EHI 0-1km Shear LCL SBCAPE
 
5 PM CDT Mesoanalysis Graphics
Sig Tor Parameter
Effective Shear
Effective SRH
MLCAPE
850mb Analysis 500mb Analysis Surface Temp/Dewpoint No Satellite Available
0-1km EHI 0-1km Shear LCL SBCAPE
 
7 PM CDT Mesoanalysis Graphics
Sig Tor Parameter
Effective Shear
Effective SRH
MLCAPE
850mb Analysis 500mb Analysis Surface Temp/Dewpoint No Satellite Available
0-1km EHI 0-1km Shear LCL SBCAPE

These mesoanalysis graphics were captured every two hours and they show the evolution of the near-storm environment as the afternoon progressed. There was a combination of large amounts of shear and instability, and that provided favorable conditions for many tornadic supercell thunderstorms.

 

NWS Services

The National Weather Service offices across the region were busy on June 17th, keeping people informed by maintaining a steady flow of information and issuing advance warnings.

The above graphic (click for larger) illustrates the flow of information from the NWS Offices in Bismarck, Grand Forks, Duluth, Minneapolis, La Crosse, and Des Moines. This is broken down into 10-minute blocks of time, and then color coded based on how many non-routine products were issued by those particular NWS offices in that time frame. “Non-routine products” that are issued by the National Weather Service are ones that are not issued on a regularly scheduled basis. This includes anything from Tornado Warnings to updates for any routinely issued products.

In total, 519 non-routine products were issued by those 6 National Weather Service offices in approximately a 12 hour period. The busiest timeframe was between 3 PM and 6 PM when 40.4% of the non-routine products in question were issued.

The above graphic (click for larger) shows how many Tornado Warnings were in effect at any given minute during the entire outbreak. It is broken down by individual NWS Office, by total number of warnings, and by times that more than 10 Tornado Warnings were in effect. At the height of the outbreak, there were 18 Tornado Warnings in effect at the same time across the region.

In total, 87 Tornado Warnings, 83 Severe Thunderstorm Warnings, and 3 Flash Flood Warnings were issued by the indicated National Weather Service offices. The average lead time for Tornado Warnings during this event was just over 19 minutes. 279 follow-up statements, under the titles “Severe Weather Statement” or “Flash Flood Statement”, were also issued in the same time frame.

In the wake of the tornado outbreak, National Weather Service offices assisted each other with damage surveys. The offices in Grand Forks, Duluth, and Chanhassen all conducted damage surveys into surrounding forecast areas, and collaborated on the information gathering process. The graphic to the right shows where some of these damage surveys took place, with the color-coded arrows.

The close collaboration of the NWS offices in the area allowed the surveys to be conducted as soon after the outbreak as possible, and allowed for information to be published quickly in the days afterwards.

 

Historical Significance

Comparing the significance of tornado outbreaks across time is a difficult thing to do. Many improvements in technology, weather education, and severe weather reporting over the past half century have contributed to an increased ability to document extreme weather events. Beyond population increases, things like cell phone technology, the internet, and increased vehicle use have made witnessing, recording, and reporting severe weather much easier in recent decades. The National Weather Service Doppler radar network allows meteorologists to track and document thunderstorms more easily, and national field campaigns like VORTEX and VORTEX2 have increased our knowledge of the processes surrounding tornado formation.

As a result of all those advancements, the number of tornado, large hail, and damaging wind reports have been increasing with time. In fact, the average number of tornado reports logged in recent years by the National Weather Service offices across the country are about double what was reported back in the late 1950s and 1960s.

With that in mind, the June 17th tornado outbreak was still one of the largest and most significant on the record books in both the Northern Plains region and in the state of Minnesota.

Here are some rankings at the time the outbreak occurred. Note that as time passes, these rankings may fluctuate if other larger outbreaks occur.

  • Minnesota State Record: most tornadoes in one day in Minnesota.
  • 2nd Largest Summer Outbreak: second most number of tornadoes in a tornado outbreak in June, July, or August.

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