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A quantitative measure of winter season severity
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WDI PRODUCTS: DownloadsGeneral Information: WDI Paper (HTML) WDI Paper (MS word) Winter Forecasting: MS PPT Presentation: Forecasting with the WDI 2002-2003 Winter Season Outlook for central PA Graphics and Analysis: Insightful Products Derived from WDI algorithm [Feb 2003] |
New additionsIntroduction to the WDIWelcome! Have you ever wondered what the recent mild winters were like in other locations in the United States? Or, just how mild they have been compared to winters of the past? The Pennsylvania Climate Office is developing an index designed to answer these questions as accurately as possible. The recent spate of very mild, snowless winters in the Northeast is unprecedented compared with "normal" winter weather. Yet just how disruptive is a typical winter lead to the development of an index that could compare a tough winter in Little Rock, AR with a harsh Minneapolis winter and rank them with parity. The components of a disruptive winter are the degree of chill and the amount of precipitation, however how to capture their effects posed the first challenge. A persistently cold winter without daily records would need to be accounted for, especially if only a small amount of snow fell, but stayed on the ground for many days. The giant super storms of mid 1990's would also need to be incorporated without tipping the scale too heavily in their favor. These were the concerns in designing the index. Ultimately, the local climate would need to dictate what was common to an area. The season from November to March was selected as the five months of general winter. The departures of monthly means for temperature and precipitation were chosen as baseline measurements. Daily values of extreme chill, snowfall, rain amount and ice accumulation were also considered. Together, there were seven components of the WDI that assess the effects of a winter overall while including noteworthy daily events as well. For more details on the specifications of the index, see the complete WDI paper. Important Notes:The definition of the WDI index has not yet been settled and is subject to future changes. This includes the computation algorithms and formula, component names, and the value scale. New index values will be computed every year as the data from the sites becomes available. When viewing WDI products it is important to note when the data points where generated, for example, the value of the 1950 WDI at a given site computed in 1993 will differ slightly from the 1950 value computed in 2003 (10 years later). This is becuase the addition of 10 years of data will likely change the climatological values used in the algorithms. WDI Value Scale:This following table shows how to interpret the values of the WDI.
WDI Climatology:The following graphics show the average value (top) and standard
deviation (bottom) of the WDI across the contiguous United States, for the
period of record for each location.
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