SEASONS: London has a four-season year. Spring (April and May) sees new leaves on the trees and seeds sprouting from the warming earth. Summer (June through mid-September) has long days, with the vegetation in full foliage. Autumn (mid-September through early November) brings the withering away of the summer annuals, the fall of leaves from deciduous trees, and the first frosts. Winter (early November through March) is the season of short, cloud days, below-freezing temperatures, snow, and the vegetation in its dormant phase.
SUNNIEST MONTHS: London isn't known for its sunshine, but June through August manages to get a respectable amount. In general, only 33% of the year's daylight hours will be sunny--from a high of 41% in May and June, to a low of 16% in December. Clear days are not common, with April and May getting the most (about three days each month). Whenever the sun does shine, Londoners are enthusiastically appreciative, and make the most of it.
WARMEST MONTHS: June, July, and August are the warmest--although days are more often mild than warm, and are almost never really hot. The hottest temperature of the year will be around 87░, and will probably occur in July, while the newspapers scream "Heat Wave Strikes Britain", and businessmen in three-piece woolen suits drop like flies.
Very, very rarely will the nights be hot enough to require any sort of room-cooling. It's more common for summer visitors to wake up in the morning begging for the heat to be turned on.
COOLEST MONTHS: Just as the summers aren't very warm, the winters aren't very cold. January and February are the coldest of the bunch, but even then only two or three mornings a week will be frosty. On three or four occasions during the winter months, the afternoons will fair to rise above freezing
--usually during an outbreak of Arctic weather. The coldest temperature of the year will be around 21░, and will probably occur in January.
Snowfalls are common enough during the winter months, but the ground is rarely snow-covered in the city past noon of the following day. Winter rain is twice as common as winter snow.
DRIEST MONTHS: There really aren't any dry months. Precipitation is pretty evenly distributed over the year in terms of frequency, with the early part of the year getting a very slight edge in "dryness". Some 57% of the year's days will get no measurable precipitation; that is, they will get less than a hundredth of an inch. A "dry day" in the table, however, is one with less than a tenth of an inch--a more useful measure. It takes at least that much to wet the ground under the trees.
Much of the rain that falls comes as a persistent light rain or drizzle
--what the Irish call a "soft" day. London gets more than four-hundred hours of rain per year. This averages out to more than seventy minutes per day, if averages mean anything!
THINGS TO KNOW: London will often have a distinct "urban heat island" effect. Under windless and rainless conditions (or near), the city center will be many degrees warmer than the outlying suburbs. This is especially noticeable at night and in the winter. Precipitation of any kind diminishes this effect, and a strong wind will eliminate it completely. The table data are for the city center, not the outlying airports.
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