by: Adnan Akyüz, Karsten Shein, Mike Asmus
Volume 2013, No.1, 31 May 2013
Trace is the amount of precipitation that is less than 0.005” (AMS, 1959). Generally, it is not a measurable amount but just enough to wet the rain gauge that it is observed in. It is a global practice that “T” (indicating “Trace”) is entered in daily precipitation records such as the National Weather Service form B-91 under the precipitation column. Although trace is not a quantitative value, it is valuable information to better assess the weather condition of the day. However, when the precipitation data are tabulated, most spreadsheet programs do not know how to deal with a character that is not a numerical value. We explain a procedure for including trace observations when evaluating precipitation behavior over a period of time or between multiple time periods. This procedure temporarily assigns a computationally insignificant value to trace observations in order to incorporate those observations into database calculations (e.g. number of precipitation days) as well as also greatly reduce the chance of ties in the precipitation rankings. Our procedure allowed us to separate individual precipitation events in perspective especially in ranking tables without changing accumulated monthly, seasonal or annual precipitation values, thus preserving the climate history of the location.