SEASONS: Lisbon has a three-season year. Spring (mid-March through mid-May) is a season of blossoming and burgeoning forth, as the rains slowly taper off. Summer (mid-May through the first heavy rains of October) is dry and sunny. Winter (from the first heavy rains in October through the middle of March) is the season of rain and short days. Since most of the trees are evergreen (including the oaks, citrus, and olives), there is no "fall".
SUNNIEST MONTHS: Except for December (and that just barely misses), every month in the year gets half or more of the available sunshine. July and August, however, will get the most. In general, 65% of the year's daylight hours will be sunny--from a high of 83% in August, to a "low" of 49% in December. July and August will also get the most clear weather--about two days out of three.
WARMEST MONTHS: Mid-June through late September. Warm to hot days with mild nights characterizes Lisbon's summer. Most of the time, the winds off the North Atlantic Ocean keep Lisbon's temperatures from getting as hot as they otherwise might. However, when the winds fail the temperature climbs, and spells of 90░ and hotter weather will set in. The hottest temperature of the year will be around 98░, and will probably occur in either July or August.
From June through early October, most nights will be hot enough that you will sleep better with some sort of room-cooling.
COOLEST MONTHS: The December through early March season is chilly and raw, but not really very cold. This time, the winds off the ocean keep things from getting as cold as places farther inland. Frosty mornings will occur, but only about every third year or so. The coldest temperature of the year will be around 33░, and will probably occur in January. Snow flurries are rare, but not unknown.
Crops continue to grow during the winter months, especially grains and some vegetables. The grain harvest is usually in the late spring or early summer.
DRIEST MONTHS: Every month get rain on less than half of its days, but July and August are the driest by far. Some 69% of the year's days will get no measurable precipitation; that is, they will get less than a hundredth of an inch. July and August will have 93% such days, whereas January will get only 53%. 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.
THINGS TO KNOW: Despite its location on the Atlantic Coast of Portugal, Lisbon shows a typical "Mediterranean" climatic pattern, with its winter rain and summer drought. In this, it is more "Mediterranean" than northern Italy, which lies on that sea.
Lisbon 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 suburbs--but the difference is not great in this case.
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