Wednesday, June 8, 2011

Clouds associated with severe weather.

            Clouds can be fascinating to watch. I don't know about you, but I've spent time laying on the ground just watching clouds. OK I will admit it,  I didn't have a lot going on that day,  still watching the clouds was enjoyable. There are 10 Main cloud Types, at sometime in the near future it is my hope to do a couple of post on the subject of clouds.  In this segment, I will give you a little description of a few of the different clouds associated with severe weather. This will help you identify what you're seeing when severe weather is approaching.

Shelf Cloud:

            This type of cloud is common and is found along a storm's gust front. a shelf cloud is attached to the parent cloud and looks a lot  like it's name suggest. A shelf cloud is created by the rain-cooled air from the storm. As most of you know, the air is warmer at the surface and colder aloft.  There is often a atmospheric cap several thousand feet off the ground where the temperature raises briefly. Most of you have heard the WTEN weather team say " The atmosphere is capped" what this means is there's a warm pocket of air aloft that's keeping a lid on things. A cap works like a closed bottle of soda, if you shake the bottle-up all is fine as long as the bottle cap is in place. However, if you remove the cap... the soda inside will explode. An atmospheric cap works the same way, as long as the cap is in place nothing happens. But, if  the cap weakens or breaks the developing thunderstorms will explode. The warm air being lifted above the cap is what you are seeing when you see a shelf cloud.  The process develops like this:  as the rain cooled air rushes outward it becomes a wedge that forces the warm air up. this forms more updrafts in turn the updrafts will form more precipitation which leads to more cold air flowing outward and new updrafts created and so on.

In this image you can see the downdraft behind and the warm air in front moving up and over the shelf cloud

Roll cloud:
            This type of cloud is fairly rare,  unlike shelf clouds, roll clouds are completely unattached from a parent storm cloud. This type of cloud is long and tubular in shape. they can be startling to see because they appear to be rolling across the sky. Although you may think it looks like a tornado turned  sideways, it is not associated with tornadoes at all.

                                                              Image of a roll cloud.
            These are  rounded sack-like protrusions hanging from the underside of an anvil cloud. This type of cloud doesn't produce severe weather. But, it's normally seen in severe thunderstorms. They like to form upwind of the updraft. As a chaser, you always look for this type of cloud, while it doesn't guarantee a tornado will form,  it does indicate the storm has a good chance to produce one.
                                                  Image of mammatus clouds

Beaver tail and Tail clouds:

            These types of clouds are inflow bands into a storm. Some confuse tail clouds and beaver tails. The major difference is a beaver tail will be attached to storm base area, whereas the tail cloud attached to the wall cloud lowering.

                                                  Above are images of beaver tail and tail clouds
Scud clouds:
            Scud's are low detached ragged looking clouds. They tend to rise and may exhibit lateral movement. Scuds are not dangerous. However, scud clouds can often be mistaken for a developing tornado.  You tell the difference  by watching the cloud to see  if there's any rotation with it;  if you see any rotation then a tornado has a high chance of forming.

                                                     Pictures of scud clouds

Funnel Cloud:
            A funnel cloud is a funnel-shaped cloud spinning at high velocity.  Normally it extends from the base of a cumulonimbus or towering cumulus cloud. A funnel cloud is usually seen as a cone-shaped or needle like protrusion from the cloud base. If a funnel cloud touches the ground it becomes a tornado, or a waterspout it was over water. If you spot a funnel cloud that's nearby take shelter immediately, as it may suddenly become a tornado.  However, if you feel there is time to safely report it you should do so.
                                                    Below are three pictures of funnel clouds

Cold air funnels:
            Unlike the normal funnels associated with severe thunderstorms, cold-air funnels are generally associated with partly cloudy skies after the passage of a cold front. it is very rare for them to touchdown. But if they do they become a weak tornado. My next blog post will be on Non-tornadic severe weather
                                                         Picture of a cold air funnel

Wall Cloud:
            A wall cloud marks the lower portion of a very strong updraft, usually associated with a supercell or severe multicell storm. It typically develops near the precipitation region of the cumulonimbus. Wall clouds can range from a under half a mile wide up to around  five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. Wall clouds that exhibit significant rotation and vertical motions often precede tornado formation by a few minutes to an hour.
                OK so you think you see  a wall cloud. Here are a few things to ask yourself,  First is it in the right region of the storm? Are you seeing a low hanging cloud on the forward flank of the storm or the rain free base? Another question to ask is  this feature pointing toward or away from the rain? Shelf clouds generally point out away from the precipitation while wall clouds generally point toward the rain. Is this feature rising? Slowly rotating? Intense rotation? Or bowing out? If you determine you're seeing a wall cloud report it to the NWS or local law enforcement.
            One other question I've been asked  Is it possible to have a tornado that doesn’t have wall cloud ? Absolutely!  Also if you're dealing with a  HP supercell the wall cloud could be in the NE quadrant of the supercell. So unless you're close, you would never see it from a distance away because you will be blocked by wrapping rain curtains.

                                                   picture of an developing wall cloud

           Well that's it for this installment. I hope you found this informative. The next installment will be on non-tornadic severe weather.  I will go into more detail on such things as Bow echo's, MCS, Microburst, and Hail.

Rebecca Ladd.

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