Workshop on Indices and Indicators for Climate Extremes, Asheville, NC, USA, 3-6 June 1997 - Breakout Group A: Storms

The Working Group on Storms considered tropical cyclones, extratropical cyclones, thunderstorms and their associated winds and effects other than on temperatures and precipitation (which are dealt with by the other working groups) to be in their purview. Changes in observing systems and distribution of observers and people impacted by these phenomena confound trend analysis. In light of the difficulty of assembling homogeneous time series of small-scale phenomena such as thunderstorms, tornadoes and hail, and also the problems in wind measurements, the working group recommends that indices of wind be developed by taking advantage of long surface (or sea-level) pressure measurements and analyses. Because wind is a vector, two pairs of readings that are orthogonal are desirable. Instantaneous values over about 1000 km scales are desirable to generate statistics relevant to wind extremes. Recommendations are given on how the data might profitably be processed. Several other recommendations are made concerning data acquisition and processing, some of which apply to reanalysis of past data and some apply to future processing of data. Various 'extremes indices' are also suggested.