Kalymnos is known for its dry climate, and year-round climbing is definitely possible. Still, some periods are better than others.
Autumn
The ideal climbing period for Kalymnos. The weather is generally good with a comfortable temperature, so you can climb all day. It rarely rains in Kalymnos during September and October, and from mid-October even climbing in the sun can be a real pleasure. The sea is still warm enough for swimming even in early November.October is certainly the most suitable month and this is when the number of visiting climbers reaches its peak. If you prefer to climb in peace and quiet, you had best avoid very popular sectors such as Odyssey, Grande Grotta, Arhi and Spartacus. Instead you can go somewhere like Galatiani, where the climbing quality and style are just as amazing and the sector will be all yours! In November the number of climbers dwindles and temperatures are slightly cooler, therefore better for sending your projects. The chances of rain are higher, but even when it rains, these autumn showers only last a few hours. You can usually climb after the rain, as the crags dry quickly. Despite the fact that most of the tourist shops in Masouri close around November 15th and the village resembles a ghost town, you can always find some rooms to rent, restaurants and mini markets that stay open just to serve the climbers. If, on the other hand, you are looking for a livelier spot, Pothia is the right place for you, a town with 15,000 inhabitants and lively all winter long.
Winter
Don’t be surprised if you end up climbing in your T-shirt on Christmas day. Good weather on Kalymnos in the wintertime is frequent. Rainy days are few and periods of rain don’t usually last long. Arhi and the crags surrounding it are the most suitable crags for winter climbing in Kalymnos, as they are sheltered from northerly winds and get most of the sun from mid-day onwards. December offers some of the most magnificent sunsets on Kalymnos. By tradition, numerous climbers visit the island during Christmas holidays and they form big companionable groups as they meet up in the 2 or 3 restaurants still open in Masouri, Elies and Myrties. Although January and February are considered ‘difficult’ months, weather conditions are still fairly good: the average temperature is around 10-12º C and sunny days are frequent.
Spring
Conditions are similar to those in autumn, and so it is an equally brilliant time to go climbing on the island. In addition, the landscape teems with wild flowers in the spring, despite the lack of trees. Breathe in the fragrant air on your walk to the crag. The chances of rain in spring are somewhat higher than those in autumn; and the sea is too cold to enjoy. Note that, if the preceding winter has been rainy, the tufa may be seeping; stalactites sometimes drip during the spring and are more inclined to break as they are softer. However, this does not necessarily mean a halt to climbing on stalactite-and-tufa routes in places like the Grande Grotta. You can climb inside the caves even when it rains, but do not climb in the (rare) event of a thunderstorm. You are in the midst of nature and climbing on wet rock in the lightning is not a good idea. The best-protected caves in the event of rain are usually at the east-facing sector Three Caves in Telendos, since rain comes in primarily from the northwest. Weather conditions in April are similar to those in October, and a number of climbers choose to spend Easter holidays on the island. May weather is relatively inconsistent: it is a rather warm month, but if it’s a windy day and you are belaying in the shade, you will definitely need that fleece.
Summer
A mistake commonly repeated is that climbing is not possible during summer because of very hot conditions. The Greek islands, including Kalymnos, are actually known for their summer northerly breezes (the meltemi). The stuffy, humid climate plaguing most other European climbing areas is not the norm here. If it happens, it is the rare exception. The only rule to follow is ‘don’t climb in the sun!’ At crags which are in the shade, a refreshing summer breeze makes climbing pleasant, and on most summer mornings you might need long sleeves if you belay in the shade. We have supplied useful information in the pages of the guidebook to help you choose the ideal sector and the right time to go climbing in different seasons. Note that on hot and windless days the rock can feel a bit ‘sweaty’ until about 10.00. June is not much different to May, and the sea is still rather cold. Although July is perhaps the hottest month in the year, you can always choose a shady crag to climb comfortably. In August the crags are in the shade longer, due to the lower course of the sun. Owing to their western or southwestern orientation, most crags are in the shade in the morning. If you wake up early, head to Odyssey, Afternoon, Spartacus, Kasteli and Symplegades. You can climb in the shade from 09.00-14.00 and relax on the beach afterwards. If you oversleep, you can instead climb at Summertime, Local Freezer, Vathy and Irox (on Telendos) or, a little later, at Symplegades. On a final note, even though August 1st-15th is the peak of the Greek tourist season, Kalymnos is in a much quieter category altogether and very conducive to a family climbing holiday.
Source: www.climbkalymnos.com