Why cities on the same latitude as NYC have different weather

A ride around the world at the 40-degree latitude where New York City sits will have you move through cities in Spain, Italy, Turkey, and China. 

Madrid, Naples, Istanbul, Beijing, and New York are on the same parallel. Even though different cities can be along the same latitude, they don't always have the same weather. Why is that?

It is because of where each city is located, according to meteorologist Laura Paterson of the World Meteorological Organization, a specialized agency of the United Nations.

Weather in New York

New York being on the 40-degree latitude gives it hot summers but it also has good winters and nice seasons because of where it is located, Paterson said.

"The fact that it's on the coast, on the border of the sea and the land, that'll influence the weather for New York City," she said. "So it would be different if it was just an island in the middle of the ocean. And it would be different if it was in the middle of a continent thousands of miles away from any coast."

Other factors are at play as well, according to meteorologist Steven DiMartino, the owner of NY NJ PA Weather.

"Anything from the type of waters that you have — whether it's salt or fresh water, how large those waters are, how warm and cold they get," DiMartino said. "Your proximity to mountain ranges and also deserts and plains, how that impacts the wind coming off those locations. And also now because of a man-made influence, where you are in those cities, called the urban heat island effect."

New York City experiences what is classified as a humid subtropical climate zone. If we were to travel around the world at New York City's 40-degree latitude line, what kind of weather would we experience?

Weather in Madrid, Spain

The weather in Madrid isn't really influenced by the sea, according to Paterson.

"They have a tendency to be a bit drier and warmer during the summer months than New York City," Paterson said.

Weather in Naples, Italy

The weather in Naples is influenced by the water, according to Greg Carbin, the chief of forecast operations of the National Weather Service's Weather Predictions Center.

"It has a tendency to be a little bit warmer in the summer," Carbin said. "Perhaps the same amount of precipitation around the rest of the year."

Italy's weather is also influenced by the Mediterranean Sea and the warm, dry air masses coming from Africa. It has a different atmospheric set up from New York's.

"In New York in the winter, we get the air coming straight down from Canada," Paterson said. "Whereas in Naples, it's usually tempered by the Mediterranean Sea. They generally don't get temperatures below freezing that often."

Weather in Istanbul, Turkey

The weather in Istanbul has some similarities to the weather in Naples.

"It is similar to Naples where they have coasts quite a lot around them, so the temperatures are a little bit tempered by that," Paterson said.

Weather in Beijing, China

Winters in Beijing are greatly influenced by Arctic Siberian air.

"And so the extremes in winter in Beijing can be greater than those you would see in New York City," Carbin said. 

Temperatures can really plummet, DiMartino added.

"In fact, in one year in 2006, they had the worst winter they ever had where temperatures were sustained at around 16 below zero," he said.

A desert also influences Beijing's weather.

"In the spring, they actually get the air coming across from the Gobi Desert," Paterson said. "So that also brings poor quality, sometimes sand and dust storms associated with that."

Weather in Northern California

Northern California has a reverse situation from New York City.

"There you have a cooling influence from the Pacific Ocean," Carbin said.

That cooler maritime air mass greatly affects coastal cities like San Francisco, which experiences fog throughout the year.

"Out of all the [places] we've reviewed here, probably the most unusual one would be California because of the influence of the Pacific Ocean just to its west," Carbin said.

"It kind of teaches you how volatile and versatile weather is and how you constantly are learning something new every day," DiMartino said. "And how just because you're on the same latitude doesn't mean that you will be able to use the same forecasting techniques. So you're learning something new every time."

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