Georgia is protected by the Caucasus mountains against cold air from the north and receive from the Black Sea warm, wet air. West-Georgia has a wet subtropical climate, whereas in east of Georgia the climate vary of rather wet to a more continental climate. Above the 2500 meters an alpine-climate dominates without real summer and above 3500 meters you will find the everlasting snow and ice.
The plateaus and slopes of the small Caucasus is drier and has a steppe climate. The weather in the Caucasus is generally more stable than the weather in the Alps. July and August are the best months for tourists, but even in this period it's possible to have temperatures of -10°C in the valleys above the 3000 meters. Below the 700 meters the temperature even comes in the coldest month of January almost never under the freezing point. The warmest month is July with average 25°C in the lower country. The temperatures in the mountains vary average between -5°C in February to 17°C in July and August. In Svaneti the winter lasts average eight months with an average temperature of -15°C. On the high plateaus of Javakheti the temperature can decrease up to -30°C. At the coast of Adjara the temperature varies between 6°C in January to 25°C in august. In the east of Georgia the temperature varies between 0°C in January to 23°C in August and in the south between -2°C in January to 20°C in August.
Georgia has especially in summer relative high UV index. Protection against the sun is needed. Below you find a chart with the UV index for Tbilisi. An index of 6 and higher means that your skin is burned fast by the sun. The total hours of sun is between 1500 and 2600 hours per year.
The west of Georgia experiences the whole year heavy rain fall which can run up to 2800 mm per year in Abkhazia and Adjara. In the east of Georgia there is 300-600 mm rain fall per year. Tbilisi has 462 mm rain fall per year. In the mountains there is approx. 1800 mm rain fall per year.
Generally the weather in Georgia is amazing for travel all year long and each period has what to do. The weather for sightseeing is ideal at any time of the year. If you would like to visit Tbilisi and the regions around Tbilisi the best months would be September and October, because the temperature will be around 25 degrees Celsius and the weather is less changeable. If you would like to visit the mountain regions and hike above 2000 meters the best months are June, July and August. Mountain areas are less reachable during the period from November to June, because the roads to the mountain villages such as Ushguli, Stepantsminda, Omalo and Shatili can be closed due to heavy snow fall. Winter sport is quite popular in Georgia and the best period for it is from end of December up to May. Georgia has several great winter sports areas, the most popular are Gudauri, Bakuriani and the newest ski resort in Mestia.