Nocturnal Heat Island Intensities and Relevance to Forecasts of Mixing Heights

Abstract

Daily minimum temperature differences for 1964 for pairs of urban and rural stations in 31 United States cities are summarized. The indication is that early morning urban-rural temperature differences vary over a large range. In the cold season the range of temperature differences from the 10th to the 90th percentiles (inclusive) is 10°F or more at a majority of the cities. The results further indicate that the technique of assuming a constant urban-rural temperature difference in forecasting morning mixing heights is questionable. It is suggested that the Summers technique (or a similar method) for calculating heat island intensity be considered a replacement for the constant value temperature-difference technique used in forecasting mixing heights.