Examples of research documenting this can be found at: Most often the tornadoes occur from the apex of the bow echo northward. Often this occurs when the bow echo interacts with some boundary, such as an outflow boundary from earlier convection. It has been well-documented by the BAMEX study and others that tornadoes do occur along the leading edge of bow echoes. I too, am too chicken to answer that question. So could a true tornado (not a gustnado or rising smoke) occur under a shelf. This obviously is another example that is NOT a tornado. This causes the air within this boundary (gust front) to rise to the nose of the shelf. Or perhaps you'll get a 'smokenado' like the one I took in the picture below where the smoke is caught at the intersection of the outflow speeding out from the left and meeting the rising inflow from the right which is heading into the shelf aloft. What you often get are gustnadoes or spinups simply caused by the strong outflow - NOT rooted into any cloud base. So for the vast majority of the time, a tornado here is quite unlikely. Therefore, with this cold and strong outflow (which as a rule does not get caught back into the updraft by going up through the underbelly of the shelf cloud), nothing of any significant buoyancy is able to get rooted below the shelf to create. This undercuts anything that is trying to get surface based. The problem with tornadoes in these situations is that you generally have the strong outflow at the surface. That's because the inflow is coming in through the shelf cloud and the updraft is on the front side of the storm. There may be a great shelf out front, and the reflectivity has the deepest reds on the "eastern" side of an eastbound squall line. This air rides up above the surface outflow and enters the storm and rises once it gets to the tower. Sure you have the outflow below at surface level, but what makes a shelf cloud a shelf cloud is the fact that there is this inflow aloft, just above the surface which gives it the shelfy appearance. Something that a lot of people don't really comprehend is that a shelf cloud itself is an updraft area. Well I tend to be a bit rash in my comments, so I'll bite and get the heat for it. 151 views of this post and nobody wanted to bite. Share your favorite shelfies (photos or video of shelf clouds) to our /photos gallery, our Facebook page, or via Twitter MORE PHOTOS: 10 Spectacular Clouds | Earth's Highest Clouds | Hole-Punch Clouds) MORE ON WEATHER.Well this post was overlooked, and I'm sure on purpose! Nobody wants to say that they believe a tornado can come out of a shelf cloud. The National Weather Service in Lubbock, Texas, documented a spectacular case of cold-frontal roll clouds in late September 2007. Either the gust front surged well away from the parent thunderstorm(s), or the thunderstorm(s) may have fizzled, leaving this remnant roll cloud.Īdvancing cold fronts have also triggered roll clouds on occasion. Unlike a shelf cloud, the roll cloud is detached from its parent thunderstorm(s). Wind gusts once the shelf cloud has passed may be quite strong, causing downed trees, tree limbs and power outages. When this warm, moist air condenses, you see the shelf cloud.Īs the shelf cloud passes, you feel an abrupt shift in wind direction and increased wind speed, followed within minutes by heavy rain or hail. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. Rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. What you're seeing in a shelf cloud is the boundary between a downdraft and updraft of a thunderstorm or line of thunderstorms. ( PHOTOS: Scary Clouds That Are Not Tornadoes) While menacing in appearance, shelf clouds are not tornadoes or wall clouds. Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. To understand how roll clouds form, we first must explain how shelf clouds develop. The first two photos in the slideshow from Lake Hendricks, Minnesota, on June 20, 2015, show a terrific example of a roll cloud. Based on their appearance, we certainly understand why.Ī more rare variety of this type of cloud, a roll cloud, resembles a giant rolling pin in the sky. A shelf cloud, also known as an arcus or arc cloud, may be the most frequently submitted cloud photo to our photo gallery and Facebook page.
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