Athens is one of those cities that are enjoyable to travel to no matter what time of year it is.  Many people prefer traveling to Athens in the summer to get the most enjoyment out of the sea there.  July and August are the busiest months of the year in Athens in terms of tourism.  However, tourists come to Athens at all times throughout the year.  One travel tip that visitors should be aware of is  that the week in August when schools start around the world (usually the week of August 15th) is typically a very slow tourist week in Athens and many places offer discounted rates at that time. This is because of Virgin Mary celebration (August 15), which is seen as the peak vacation escape time for Greece and Athens is left half-empty (lots of small shops are closed for a few days in the week around Aug.15 and business is running slow in the city, however, travelling from the city is very busy and, if you plan to take a ship from Pireaus to any island, the plane to any destination or a bus you must have made reservations very much in advance).

In terms of weather, visitors coming to Athens in the summer can expect for it to be hot during the mid-afternoon but relatively comfortable throughout the rest of the day, with nights being cool.  Visitors from humid climates should be aware that the summer months can be exceptionally dry in Athens, thus the feeling of a temperature of 33 Celsius in Athens can correspond to a feeling of 26 in humid conditions.  Humid heat and rain in summer is a rare phenomenon. Athens is also affected by the northern winds of the Aegean (called "meltemi"), which can get quite strong in summer, thus making the hot weather less felt -- but problems may appear in sea transport at times, because of rough sea. Regarding the beaches close to the city, the northeastern coastline is directly affected by the wind, so the sea often gets somewhat rough (of course, much less than in an ocean) in summer, but it is much less rough in September. The southwest coastline beaches are warmer and seldom get rough (it only happens on the occasion of southern winds, which happens very rarely). One must bear in mind that there is usually a significant difference of temperature between the southwest (warmer) areas and the northeast ones, which can be between 3 and 7 degrees, depending on the specific area. It is for this reason that the northern suburbs (Kifissia, Drossia, Ekali) started as summer vacation areas of Athens inhabitants in the 19th century. Most common winter temperatures for Athens center is around 5-9 celsius at night and around 11-15 at daytime, but the northern wind often causes a colder feeling. On the other hand, the sun shows up quite often, which makes life easier in winter.

The winter months in Athens are the time when it is most likely to be rainy.  Occasionally, Athens will see snow during the winter, but it is not common.  In fact, it often stays warm enough for visitors to enjoy the beaches late in to autumn. Athens has mountains around, the highest being Parnitha, which is the first to get snowy in winter. The snow comes to the mountains around several times in winter, but it usually melts in a matter of days -- in that case, the northern suburbs also have a little or more snow, depending on the area. In that case, temperature in the city of Athens is quite low (bet. 0 and 7), and in rare occasions (typically not more than 3 times a year) there is some snowfall in the city centre, too. In that case, the main streets are cleaned, but one may need to put on chains to be able to drive in smaller roads in the areas of the mountains or the northern suburbs. Salt is often available in stores or public places in the northern suburb areas. 

Fall is typically rainy, but there can be occasions of fantastic sunny weather both in October and November. The same is true for March and April. May is seen as the beginning of summer, but May weather can vary substantially from year to year. But it is generally possible to swim in the southwest beaches already in May, though staying outdoors for a long time at night becomes possible usually only by end June.

 More information about the weather in Athens is available online at http://www.athensguide.com/weather.html.