Short and Long Range Air Temperature Forecasts near an Ocean

Abstract

Using a predetermined statistical scheme, forecasts are made of the daily air temperature (AT) at San Diego, starting from local antecedent information concerning AT and sea surface temperature (ST) only. These forecasts are verified by calculating skill scores (S) over 1948?79. in this maritime area such simple schemes turn out to have high S for lead times up to a mouth and small but positive S out to a year. Differences in S of the various one predictor schemes (ST ? AT, ST ? ST, AT ? AT, AT ? ST) are discussed; ST ? ST is far superior to any of the other three. For most schemes S is low in late summer, this is attributed to the shallowness of the ocean's mixed layer in that season. The effects of time averaging the predictor and/or predictand are discussed for the ST ? AT scheme. For long enough lead times averaging appears to improve forecast skill. The localness of the prognostic information carried by ST is investigated by comparing S for San Diego and an inland station (Esondido). At a forecast lead time of three days S decreases by 50% over a distance of 25 km. Further analysis shows that this decay is primarily caused by a decrease in skill of daily maximum temperature forecasts. In view of the similarity of the present results to those obtained at the Dutch coast, we conclude that local information about the state of the surface has probably enough prognostic potential to be incorporated in existing operational schemes of short and long range air temperature forecasts near oceans and lakes.