Although there's a huge difference in temperature between western Russia and Siberia in the winter, this difference is much less in the summer. Almost the whole of Russia is uniformly warm in June (although the further north you go, and the closest to the Arctic Circle, the colder the temperatures).
Average June temperatures in most of the major cities and sites of interest are above 68° F (20° C), with temperatures in the high 70s and low 80s F (high 20s and low 30s C) not uncommon. The exception is Vladivostok and the far east, which see a milder high of 62° F (17° C). Regardless, you can leave the heavy winter clothing at home in June, and just bring a light jacket and sweater.
Another important factor is that the further north you go, the longer the days. Towards the end of June, St. Petersburg experiences around 22 hours of daylight, with the sun setting after midnight and rising again around 2 am. While this can make sightseeing great fun, it can also be a bit exhausting, especially if you have trouble sleeping when it's light out. Don't underestimate the potential effects of the long daylight hours on your energy levels and sleep quality.
You should also expect some rain in the summer, between June and August. This is the wettest season across Russia.
Crowds & Costs
June is peak season in much of Russia. St. Petersburg in particular is busy during this month thanks to the White Nights festival, which sees accommodation prices soar. This is also a popular month to take the Trans-Siberian Railway and to visit Lake Baikal, so book transport and accommodation in advance so you don't miss out.
But of course, Russia is a huge country, and beyond a handful of popular destinations, you won't struggle to get away from the crowds. If solitude and lower prices are important to you, look a little bit outside the box and you can have it all.
Where to Go
St. Petersburg in June is very festive (as well as expensive and busy!) If classical music and dance are your thing, you can't go beyond the cultural capital in June. Book accommodation as well as concert and event tickets in advance.
Siberia is most accessible in the summer, so the Trans-Siberian Railway journey is popular, or you can fly to cities like Irkutsk to save time. Temperatures are hot and the landscape is green and alive. Lake Baikal is always a popular attraction. While you won't see it with its dramatic thick ice in June, you can access Olkhon Island, the third-largest lake island in the world and one of the highlights of visiting Lake Baikal.
A number of old historic cities in western Russia—including Yaroslavl, Kostroma, Suzdal, Sergiev Posad, and Pereslavl-Zalessky—are easily accessible from Moscow and St. Petersburg. Visiting these places, among others in the region, offer a great overview of European Russian culture, history, and architecture. There's no firm list of which cities can be included in a Golden Ring tour, so you can devise an itinerary to suit your time and interests.
What to Do
There are lots of cultural festivals in Russia throughout June, as well as the whole summer. As well as those listed below, many Russian cities celebrate their 'birthdays' in the summer, so you're likely to find an unexpected party and cultural performances in all sorts of places.
The summer is a great time to enjoy a Baltic Sea cruise, which often include stops in Finland and Estonia as well as St. Petersburg. These give a great overview of the culture and geography of the region.
To enjoy some gentle hiking, head to the Ural Mountains, which border European and Asian Russia. They're not very high mountains but they are some of the oldest on earth, and you can find vast forests, lakes, caves, hot springs, and other natural attractions. Yekaterinburg is the best access city.
Events in June
White Nights, St. Petersburg. Throughout June and July, various shows are put on at the Mariinsky Theatre and other cultural venues.
Sadko Festival, Veliky Novgorod. A festival of folk art, singing, and dancing, as well as a craft fair, held in the second weekend in June.
Russian Independence Day, 12th June. Commemorates the day in 1990 that the Russian Federation declared independence from the Soviet Union.
Moscow International Film Festival. Russia's most famous film festival runs for eight days at the end of the month.
Traveling to Russia in June? Check out these great itineraries
Trans-Siberian Rail Tour: Moscow to Beijing - 16 Days. A classic Russian journey, the Trans-Siberian is best done in summer, when the landscape is vibrant and temperatures comfortable.
Russian Capitals and Golden Ring Tour - 14 Days. Enjoy the best art, architecture, and history of Western Russia on this tour that includes the large cities as well as smaller provincial towns.
Grand Russia Tour - 20 Days. This comprehensive tour of European Russia starts includes big-name destinations like Moscow and St. Petersburg, as well as those that are overlooked by many travelers, like Kazan. Summer's an ideal time to experience Russia's natural beauty.