Like all European countries, Ukraine has four basic seasons: winter, spring, summer, and autumn (fall).
The weather can be categorized as extreme. The summers are rather hot, typically reaching temperatures upwards of 30 to 35C; the winters can be rather cold, typically reaching temperatures upwards of -10 to -20C in some areas. Then there are two brief seasons in the middle—spring and fall—that appear out of nowhere and disappear as quickly as they appeared.
Ukrainian winter typically starts around the end of October or the beginning of November. It lasts until around the end of March or the beginning of April. The first week of May usually marks the official beginning of spring; there's a week-long holiday where people travel to relax, mostly to the countryside.
By the end of May and the beginning of June, temperatures start to gradually climb signaling the start of the summer.
Where to go in the summer
June, July and August can be scorchingly hot in almost every city in Ukraine, especially in the Eastern and Southern parts of the country.
This is a great time to visit and explore the country, but I would mostly recommend spending a few days in a land-locked city such as Kiev or Dnipro and then head down and enjoy the beaches of Odessa.
While Kiev is great in the summer, I don't particularly love its climate. It can get super hot and muggy, so much so that you're always sweating regardless of where you go. Plus, you can't really escape it; there are no beaches nearby. That's why making a quick trip to Odessa is always a wise choice.
Another good option for the summer is to head out to Western Ukraine and spend time in the mountains. As soon as you climb above sea level, the weather cools down and becomes much more bearable. Once you're there, you can rent an entire cabin for the summer and enjoy the beautiful countryside, the healthy food, and the fantastic air while everyone else is suffering in the cities.
Where I spent my summer
One summer, instead of spending it in Kiev, I went and lived in another city in a different part of the country. While living there, one weekend I took a trip with my girlfriend to a nearby little town. It was one of those country-style inns with a restaurant. There was even a small pool to cool down.
In the area, we were surrounded by private homes, many of them had pools. At this point, I realized that spending a hot summer in one of those houses with a pool wouldn't be such a great idea. Unfortunately, I realized this at the beginning of September just as the temperatures started to climb back down and taking a dip in the pool was no longer a very enticing thought.
The summers are also great for dating because everyone is enjoying the weather and themselves, especially if they're relaxing by the pools or beaches of Ukraine's coastal cities.
Spring and autumn are great
I personally think that the best time to visit Ukraine would be either the spring or the autumn. Eastern European spring is absolutely gorgeous. The weather goes from cold, rainy and cloudy days to warm and sunny days. People's moods and behavior changes. The birds are chirping. The flowers are blooming.
On the other hand, coming in the autumn while probably isn't as pleasant as in spring is still a nice time to visit. The end of August and the first several weeks in September is actually a great time to visit the country. The temperatures have cooled down so that it's no longer unbearably hot but still not yet cold. This makes it ideal for exploring Ukraine's cities and countryside.
What about the winter?
Personally, I hate it when it's cold and I need to put on twenty layers of clothing before stepping outside. Never mind the snow everywhere, the slush and the ice. In fact, the worst days are those that are extremely sunny; it seems the sunnier the winter day, the colder it's outside.
I remember spending a winter in Kiev and, for the most part, the temperatures weren't that bad. It was mostly hovering around 0C with an occasional -5C or so. But, then, the week of the New Year's, it had suddenly dropped to -20C and -30C. That lasted for around ten days. That meant as soon as you step outside, you immediately feel cold—regardless of how many layers of clothing you put in.
Not fun in the least.
Fortunately, that didn't last the entire winter and temperatures quickly went back to -5C or so, which was a bit more bearable.
There are people who actually enjoy the deep winter. Some find it "romantic" sitting at home, enjoying a hot beverage while watching the snow slowly fall on the city. I'm certainly not one of those people—give me a tropical beach anytime—but I understand where they're coming from.
If you do choose to come in the winter, I have one piece of advice: make sure you stay in the center of the city which is replete with beautiful buildings and timeless architecture. Don't stay outside the city center which is typically full of rusty Soviet-era buildings and broken roads.
Staying in the beautiful city center makes the winter much more manageable.
Of course, one option is to skip the winter altogether. I know many younger Ukrainians leave the country and go overseas, to countries like Thailand and Bali. Of course, that means leaving your jobs for a couple of months and then either finding a new one when you get back or begging your old boss to take you back.
Another option is to suck it up, buy some good clothes and stay for the winter. After all, Russian cities in the north have it much worth. And, given everything, Ukraine's winter is pretty manageable.
I would give anything if Ukraine's climate was similar to Barcelona's or Rome's: long warm summers and short and mild winters. Of course, it would be even better if it closer to Medellin, Colombia's with its permanent spring, but then it wouldn't be Ukraine and instead some other country.
Instead, the existence of all four seasons gives you a chance to experience four different types of Ukraine. And, if you come with the right expectations, you shouldn't be disappointed regardless when you make that trip.