When you picture your dream European summer vacation, how's the weather?

Perfect, right? Sunny, comfortably warm air, light cool breeze?

But what if there's a heat wave, like the one about to bake much of Eastern Europe? A heat dome is expected to drive temperatures up into 90s (or mid- to high-30s Celsius) this weekend and next week.

A heat dome is caused by persistent high pressure in the upper atmosphere, which causes air to sink and compress, which drives up temperatures. That heat gets stuck, as clear skies allow for tons of sun, and the dome inhibits storm systems that would otherwise provide relief. And this one is no joke.

It's been 14 years since it reached 86 degrees in the United Kingdom in May; the forecast calls for temperatures up to 91 this weekend.

Whether your European holiday is coming up next week, next summer or next decade, a heat wave could impact it, but won't necessarily ruin it. Here are six ways you can stay cool as a Yank touring Europe.

Find Air Conditioning
Americans might hear of temperatures in the 90s and think, "Sure, that's hot but not unbearable, especially inside." But unlike most places in the U.S., a lot of buildings in Europe are not equipped with air conditioning, or at least not central A/C. In fact, many of these buildings are much older than the ones in the U.S. and are specifically designed to retain heat. Even at night, it might be too warm inside.

Churches, museums, shopping centers and train stations are often cooler than outdoor streets and can provide relief during the hottest hours, typically between noon and 5 p.m. Many historic stone buildings naturally stay several degrees cooler inside. Schedule outdoor activities for the morning or evening, and find indoor activities with A/C for the afternoon.

Carry More Water Than You Think You Need
Many European cities are highly walkable, but long stretches of sightseeing in extreme heat can quickly lead to dehydration. Carry a reusable water bottle and refill it frequently at public fountains where potable water is available.

Skip Heavy Meals During The Day
Rich foods and large meals can make you feel hotter and more sluggish. Choose lighter options like salads, fruit, sandwiches or chilled dishes during the afternoon and save heavier meals for later in the evening.

Use Cooling Towels Or Portable Fans
A small battery-powered fan or cooling towel can make a major difference while standing in lines, riding public transit or walking through crowded tourist areas with limited shade.

Dress For The Climate, Not The Photos
Lightweight, loose-fitting clothing in breathable fabrics like linen or cotton helps your body regulate heat more effectively. Dark colors and heavy fabrics trap heat and can quickly become uncomfortable.

Limit Alcohol During Extreme Heat
Drinking alcohol in high temperatures can speed up dehydration and increase the risk of heat exhaustion. Alternate alcoholic drinks with water, especially if spending long periods outdoors.