A strange cloud formation ahead of this morning’s squall line

thunderstorm radar may 9 2011 squall line approaching Northfield 
As I settled in for coffee at 6 am this morning at the GBM, I checked the radar and noticed a line of severe thunderstorms approaching. I glanced out my corner office window and saw a white streak of clouds, very high up, many miles long, well ahead of the wind, rain, and pea-sized hail that eventually came after the squall line passed.

squall line approaching Northfield squall line approaching Northfield squall line approaching Northfield
Anyone know what this cloud formation is called? Is it a "line echo wave pattern" as described in the Wikipedia  section on the severe weather indicator of a squall line?


  1. The squall line look a lot like this as it crossed the St. Croix this morning near Hudson. I don’t think it hailed there, however. Thanks for posting the photos.

    May 9, 2011
  2. Nick Benson said:

    Also worth noting, the outflow boundary / gust front associated with that shelf cloud is actually visible on the radar capture you’ve got there; it’s the faint green line ahead of and parallel to the line of storms.

    May 9, 2011
  3. Phil Poyner said:

    Yeah, I think it’s most likely a shelf cloud…here are some images of other shelf clouds http://www.targetarea.net/photoshe.html

    By the way, LEWP is a term used to describe a radar pattern rather than a cloud feature. Waves developing on a squall line (as seen in the radar imagery) are of concern because of the potential for tornadic development, large hail, and high winds associated with them.

    May 9, 2011
  4. Jan Hill said:

    Really cool early-morning photos, Griff, and of course Nick knew the name of this formation. I heard shelf clouds described on MPR a couple of weeks ago by someone who had studied meteorology but never seen a “real” one until this spring in Minnesota–then I wanted to see one too. It’s good to know they visit Rice County, so I will start watching when we have squall warnings.

    May 9, 2011
  5. Griff Wigley said:

    MPR meteorologist Paul Huttner agrees with you, Nick. He put one of my photos in his blog post this morning and commented:

    It is probably a shelf cloud…a common feature at the front end of MCS.

    May 9, 2011
  6. Griff Wigley said:

    Thanks, Phil. Those are impressive photos. My dad always referred to those shelf clouds as “the squall line” but I see now that he was mistaken.

    May 9, 2011
  7. Phil Poyner said:

    Griff, your Dad would not have been completely wrong; he’s just mistaking what could have been one component of a squall line for the entire thing. Looking at the radar image, the entire feature could very well have been a squall line…I’d have to look at some other tools to be sure http://www.theweatherprediction.com/habyhints/150/ Within the squall line itself it’s possible that LEWPs or bow echoes could develop in radar imagery, and that you could see the formation of other features such as wall clouds, shelf clouds, or roll clouds. Shelf clouds in particular are often associated with squall lines.

    May 9, 2011
  8. Griff Wigley said:

    Wall clouds, shelf clouds, roll clouds… jeesh, I’m going to have to take a course in meteorology, as I know far less than my wife thinks I know.

    May 11, 2011
  9. john george said:

    Griff- I just hope the meterology course doesn’t cloud the issue for you. 😉

    May 12, 2011
  10. Griff Wigley said:

    No worries, John. But I am thunderstuck at your ability to create a pun out of most any situation.

    May 13, 2011
  11. john george said:

    Hail to the experts, Griff! Funny how puns can have a cumulus effect.

    May 13, 2011

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