The weather at any place changes daily, sometimes hourly. Climate is most simply expressed as the average weather over a period of several years. Day-by-day variations in temperature, rainfall, atmospheric pressure, wind and sunshine in a given geographical region constitute the weather. Climate, in contrast, is the synthesis of such weather variations over much longer periods of time, usually years. As for weather, it is convenient to measure climate quantitatively, by using average temperature, average pressure, average rainfall and so on. Averages may be calculated monthly, yearly or over a number of years. Sometimes it is also helpful to know climatic extremes. Two places in different parts of the world may have the same average yearly temperature, but different ranges throughout the year. Manchester (UK) and New York (USA) have similar annual averages, but the yearly average temperature range for New York is twice as large as that for Manchester, with much colder winters and warmer summers.