However, there are other permanent factors that make for contrast in British weather, the effects of which are much more predictable -proximity to the sea, the height of land, and the exposure to the wind. The highlands and the mountains lie mainly on the west and bear the brunt of the westerly winds off the oceans, the plains lie mainly on the east, nearest and most vulnerable to continental influences of frosts and drought. The contrasts in many places are spectacularly abrupt; Snowdon has 200 in. of rain in the year, Rhyl, only 25 miles away to leeward and on the coast, has only 26 in.
On the whole, such is the persistence of warm moist winds off the warm waters of the North Atlantic Drift that mildness characterizes the whole of the western coastal areas so that the January mean isotherm of 40° F. runs up the west coast as far as Cape Wrath and the Shetland Isles. Devon and Cornwall and the south-west of Ireland have average temperatures of 43° to 45° F. in the coldest month, cattle can graze the grass that continues to grow in most years, early vegetables are grown and the Scilly Isles produce flowers at Christmas and daffodils for St David's Day (March 1st).
The most noticeable feature in the map of sunshine hours is the general parallelism of the lines to the coast (fig. 1). The south coast has an average of 1,650 hours a year (an average of 4½ hours per day) but the Welsh mountains, the Peak of Derbyshire and much of the Scottish Highlands average less than 1,200 hours (3½ hours a day). Where the mountains come close to the sea in North Wales or Scotland, one may sometimes sunbathe on the coast all day and watch the mountains covered by orographic cloud.
For such a number of reasons, then, the weather is about as variable as it could be in such a relatively small region but the extremes are hardly ever severe. The temperature rarely exceeds 90° F. or falls below zero, the heavy rain that falls in the mountains runs off quickly down steeply graded valleys where it can be stored in reservoirs which provide water for the lowland towns and cities. Only rarely does the floodwater reach higher than the alluvial flood-plain and the river's rise is thereafter gradual, giving adequate warning to those who have unwisely built on land labelled 'liable to flood'. The occasional little whirlwind (a 'twister') can unroof houses, heavy snowfalls can immobilize traffic locally and cause great inconvenience, as can the rare glazed frost and the much commoner icy roads, but fog is probably the greatest potential disaster that can happen, causing collisions and death on roads and railways. These minor crises fill the newspapers and provide a conversational gambit, but in contrast with the heat-waves in New York, or blizzards on the prairies, or floods in China or droughts in Australia, or hurricanes in Florida or tornadoes in Kansas with the roll of deaths and the cost of damage done, British weather seems indeed moderate.