<>Weather forecasts for the United Kingdom & Europe [click to bookmark this Weatherweb page]

A Brief Introduction to Forecast Cloud and 500ft Temperature Charts The charts you are currently viewing give a prediction of cloud (between about 2000ft and 18000ft) and are overlayed with forecast temperatures at 850mb (about 5000ft). The charts should give an indication as to expected moisture (cloud) and temperatures at 5000ft for each of the predicted times. Data is based on 0001 GMT last night, so a time of T+36 is 36 hours from that time i.e. midday tomorrow. By viewing the temperature at 5000ft, and the forecast cloud, one can estimate the likelyhood of icing at that level (although remember these forecasts are for planning only and you should consult the latest forecasts before flying). If there is cloud (shown by white on the forecast chart) then the air is moist, if there are clear skies (black) then the air is dry. If you are flying below this level temperatures increase by 3C per 1000ft in dry air and at about 1.8C per 1000ft in moist air. So, if temperatures on this chart are, say, -5C at 5000ft and there is cloud. You can estimate that at 2000ft the temperature will be around 0C. If there is no cloud than the temperature at 2000ft will be around +4C. These predictions are a rough and ready estimate of icing potential but do not replace official forecast given on the day of flight.