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Graph of mean SR flow for each storm depth relative layer for nontornadic supercells ( medium gray ) , weak tornadic supercells ( light gray ) and the subset of supercells producing strong or violent tornadoes ( black ) . Because these variables are available to most forecasters , and because the RUC-2 is generally a robust and timely tool for evaluating the sounding environment near supercells ( Thompson and Edwards 2000a ) , it can be used to evaluate the utility of these parameters . The large range of 250 mb SR wind speeds does imply that a wide variation of supercell structures can support the development of tornadoes , from " heavy-precipitation " supercells ( Doswell et al. 1990 ) associated with weak anvil-level relative winds , to " low-precipitation " supercells ( Bluestein and Parks 1983 ) associated with strong anvil-level relative wind speeds . Cluster developments , long pushed by environmentalists and smart-growth advocates , are finally catching on with builders who previously did not want the aggravation of pursuing special permits ,... Monday the Gulf Coast Institute had a presentation on " Portland : Myth and Reality " by Robert Liberty , who has played in integral part in shaping Portland over recent decades through multiple organizations there , including Metro Councilor ( their all-powerful regional metropolitan planning organization ) . " On some things ( such as poultry production ) , we've hit a biological barrier . News galvanizes the colonies ( April 18 ) . The author speculates that the opposite can occur with some supercells tending toward the low-precipitation end of the spectrum where strong anvil-level relative winds remove developing precipitation particles downwind from the main updraft , much as speculated by Branick and Doswell ( 1992 ) concerning the 13 March 1990 supercell tornado outbreak .