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Main Index To The Weather Watcher Thunderstom Basics What to watch for Tornadoes and Funnel Clouds Don't Get Fooled What to Report Index Safety Tips How to report quick reference Other Educational Sites |
Severe Weather Watcher Handbook
When the storm has arrivedOnce it is raining and clouds have engulfed the area, you must rely on the storm's behaviour to determine its next move. Three things to pay attention to are the precipitation,wind,and lightning/thunder. The expected precipitation pattern for most supercells is a steady transition from lighter anvil rain to heavy rain, and finally, rain mixed with or changing to hail. If this occurs, hailstones will become larger and less frequent,then end just as the lowering arrives. Always check for a lowering to the W-SW during very large hail. If rain (or small hail)begins as brief, separate showers or a sudden cloudburst when the rain curtain arrives, the system is more likely propagating forward and this particular storm will wind down without any other severe effects. Watch the wind direction. If the wind shifts to the W or N (after being S) and persists, outflow predominates and there's no immediate concern. A calm wind, after SE-SW warm winds ahead of the storm, always suggests updrafts.Unless the gust front is just about to pass (very brief calm), the main updraft is overhead and you should check the sky for a lowering. Once winds shift to the W-N and remain so, most of the danger will have shifted to your east. 60 W/E, 61 W/E Comparison of a disorganized stormy sky with a potentially severe one. In 60, thickening anvils and a scattering of lower clouds herald distant showers. There is no single focal point here. The dark cloud bank (centre) has some new convection but no inflow structure or lowerings. This scene is typical of many weaker cold fronts. But in 61, a severe storm has imposed control over the flow. A smooth, high anvil (seen top left) spreads forward from the black, distant core where a sharp boundary from rain to inflow exists. Note the inflow bands, especially the thick one at top, heading into the storm. New updrafts are concentrated along the forward side and at the SW end (bottom, centre). When the sky is drawn together like this, it is usually a severe situation. |
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Created :
2002-08-26
Modified :
2002-12-19
Reviewed :
2002-12-19
Url of this page : http://www.msc.ec.gc.ca
/education/severe_weather/page23_e.cfm ![]() The Green LaneTM, |