Climate in the southern Siberia is characterized by extreme temperature differences between summers and winters as well as between day highs and night lows. As a whole, it is quite warm here in the summer and extremely cold in the winter. The huge amount of water stored in Lake Baikal takes its effect making the weather in cities surrounding the lake somewhat milder than in the rest of Siberia.

December and January tend to be the coldest months here with average temperatures of −19 C (−2 F). Though, it is not unusual to experience the extremes of −40 C (−40 F) for a few days or even over a week in a row. By mid-March and throughout April when spring season starts it normally gets much warmer. During daytime the temperature may get to +7…10 C (+45…50 F) on average while at nights it is still often below freezing. In March and April snow is not very unusual when temperatures suddenly drop as if the winter is back. Since it is above freezing in spring time the snow that has been lying on the ground during winter already melts away. However, Baikal ice thaws out much later making air cooler in Listvyanka and near the frozen lake than in nearby Irkutsk. Summer takes a while to get started.

True summer weather does not really begin until the end of May and early June when daytime temperatures usually surpass +20 C (+68 F). The warmest period of the year is July and the first half of August. Typically, July is the warmest month for Irkutsk while at Lake Baikal shore it is the beginning of August. This is since freezingly cold Baikal water cools off air around the lake throughout June.

Lake Baikal also has rather humid climate with July again being the wettest month. Thus, weather during the summer may be very unpredictable. In July and till mid-August, we often have a couple of weeks of very hot temperatures. It may be over +30 C (+86 F) in Irkutsk reaching +33…35 C (+90…95 F) some days. This heat usually ends up with heavy rains and thunderstorms that freshens the air up to more regular temperatures. As a whole it is often nice and mild during this time of the year with highs varying around +22…25 C (+72..77 F).

Nights are still rather cool even during the mid-summer. In the early mornings it may get +12…15 C (+54…59 F) in Irkutsk and even some +8…10 C (+46…50 F) at Lake Baikal. When it rains the daytime air temperature always decreases; we never really have warm tropical rains here. At the same time when it is cloudy or rainy nights are generally warmer than the ones followed by clear days. So, it may be about +15…17 C (+59..63 F) both during day and night. Even if you visit Baikal in the summer it would be still be a good idea to have an umbrella, waterproof jacket and a warm sweatshirt to wear on chilly mornings and rainy days.

By the end of August it gets colder at nights, and it also starts to rain more frequently. Night lows drop to +5…7 C (+41…45 F) in Irkutsk and +3..+5 C (+37…41 F) at Lake Baikal. During daytime it still can be relatively warm around +20 C (+68 F). When it rains, temperature falls to some +10…12 C (+50…53 F) during the day while cloudy nights may be somewhat warmer than the nights when it is clear.

The beginning of September varies each year. Some years it may be very pleasant out with the temperatures of +16…18 C (+61…65 F) when the sun shines. This period often referred as the Indian summer may last from a week to a dozen of days. All the leaves on the trees turn red and yellow and stay on for some time before the cold fall winds soon blow them away. However, when the sky is clear it is just above freezing at nights. And September is the time when we also have first freezing night temperatures. If it is cloudy or rainy it may be +5…7 C (+41…45 F) the whole day through.

In October we can already experience the first freezing temperatures even during daytime (−2…0 C or +28…32 F). The probability of rain is also very high. It may also snow for the first time. Though, high-moisture content snow does not cover the warm ground, but melts right away. One should expect September figures to fall some 5-10 degrees (9-18 degrees F) in October. Warm boots for wet and messy days and some warmer coat, gloves and hat would be the right choice for this time of the year.