![]() I have seen scud bombs race outward from the precip area, stop, ascend into the new updraft region and grow as it transforms into a wall cloud. Last year near Pratt, KS, David Drummond and I observed a weak multi vortex tornado which developed in a similar manner along a big shelf cloud with no real apparent wall cloud associated with it. Another picture a little further north showed a nice tornado that developed in a kink or slight notch in the shelf cloud. It showed a pretty stout shelf cloud, but with notable convective properties (strong cumulus growth). I remember a great SKYWARN slide that Gary Woodall of the NWS Fort Worth had. You can even see this on radar sometimes. In reality, a new storm developed along the outflow boundary from the other storm ahead of it.classic. Another updraft then develops and transitions the shelf cloud into a wall cloud. I have seen definite shelf clouds move southward out of a storm then become stationary. Trying to force something into a specific and well-defined classic definition just doesn't work sometimes, and that's ok. As a result, sometimes the best definitions are "hybrids". Even Al Moller, a 30+ year chase veteren himself, has said that every year he chases to this day, he still sees things that makes him utter that same question. There are always exceptions and moments of "what the heck is THAT?". Not sure if you were referring to me but wanted to defend myself just in case.Īs I always say, mother nature sometimes doesn't fit into a neat little box of our scientific definitions. I do not have a great deal of formal training but I do have 13 years of storm chasing experience. Not to mention the fact that the storm was tornado warned. Those things seemed to gel with what I was seeing on radar. There was a notch in the line (inflow) and a lowering which showed some very weak rotation. That in itself makes a shelf cloud impossible. The line of storms were still inflow dominant at the time. Observing the storm myself it was clear that this reporter either needed more experience or more than likely enjoys drama! My call was simple. I actually witnessed a local news person nearly fear mongering at a gas station in Sedan, telling the employees and doing a phoner explaining how he witnessed multiple funnels headed towards town. First of all I do agree with you that there are more than enough faulty reports such as SLCs as funnels or shelf clouds as wall clouds. Looking southwest at a lowering exhibiting classic shelf structure: Curtain like appearance, pointing away from the precip core:īeing one of only a few persons that reported a wall cloud yesterday I feel the need to explain my call. We had what looked like a completely occluded base, and so were in the process of bailing, but the north end reorganized and we had a cone tornado minutes later: Your strongest tornadoes form here, while the old wall cloud fans out well to the south. In a cyclical supercell, the north end of that bowed out wall cloud is going to reorganize, tighten into a new wall cloud, and the whole process repeats. Your typical shelf clouds are usually formed by forward flanking downdrafts in multicell clusters and squall lines. ![]() At this point I would say the feature actually is a shelf cloud as the RFD is dominant. This is what happens when an updraft becomes occluded. It often continues to do so until the original wall cloud has fanned out into what looks like a regular shelf cloud. When a clear slot forms in a wall cloud, the rear flanking downdraft is in the process of punching through. ![]() So, I'd think that most anything on the leading edge of a big storm is rarely going to be properly called a wall cloud. Wall clouds should be monitored visually for signs of persistent, sustained rotation and/or rapid vertical motion. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. ![]() When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. *Wall Cloud - A localized, persistent, often abrupt lowering from a rain-free base. The glossary page for storm spotters (Norman) gives this definition for wall cloud: Wikipedia is a nice way to get a basic intro to a subject, or links to more definitive sources - but I wouldn't use them as my primary source. I'll let others with more experience answer, but I'll just put in my 2 cents.
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