How Climate Change Is Altering Western Winters

Feb 5, 2015

Map showing global temperatures in 2014.
Credit NASA GODDARD SPACE FLIGHT CENTER

You don’t need me to tell you that the winter in Utah has been rather lackluster this year. While our mountain peaks are still white, any snow we have seen in the valleys has all but melted off. According to Simon Wang, assistant director of the Utah Climate Center, this is due to how weather patterns coming inland from the Pacific Ocean have changed.

“In Utah you usually have these smaller waves coming through during winter and spring that bring fresh snow to us, that is why we have this powder-like snow," Wang said. "But sometimes the weather pattern becomes highly amplified, so that you have a wave pattern coming from the Pacific and it’s huge."

What Wang is referring to is the jet stream that comes from the Pacific Ocean and moves from west to east across the United States. This pattern directly effects what our weather looks like.

In January, NASA and the National Oceanic Atmospheric Administration released a study that found 2014 to be the hottest year globally since record keeping began in the late eighteen-hundreds.

In the U.S., states from the West Coast to just east of the Rocky Mountains experienced warmer years than average, with California, Arizona, and Nevada setting records. However, most states from the East Coast west to the Rockies experienced quite the opposite, some setting record lows. Wang said this is directly related to how the nature of the jet stream from the Pacific Ocean has changed.

“In 2013 and 2014 that pattern has amplified, meaning that when we have the jet stream of high wind speed coming from the west to the east, it goes up and down, I mean north and south, it fluctuates,” Wang said. “The bigger region that it covers, for example the north and south edge may cover from Canada to Arizona and that’s a big big wave, it contains a lot of energy. It moves much slower, and when it comes in it stays for such a long time that it tends to make the warm days warmer or the rainy days wetter."

As the jet stream moves slower, certain regions are stuck in prolonged weather patterns. For example, warmer and drier in the West and cooler in the East for most of the year.

Wang said this explains the discrepancy in 2014 temperatures between the Eastern and Western United States. He also said he knows why this jet stream is acting the way it is, and it has a lot to do with climate change.

“When there is a [global] temperature rise that is continuously rising...you will see anomalies. Some places will be hotter than the global mean, and some will be colder than the global mean,” Wang said.

One of those hot spots is in the Western Pacific Ocean.

“In the Western Pacific, that's very far away from here, the heat that has built up there, not only in the air but in the ocean, has a contribution toward these so-called high amplitude wave weather patterns that has become stationary in North America,” Wang said. "The water in the Western Pacific, the warm water there eventually modifies thunderstorms there. These thunderstorms, eventually what they do when they form is they pump up all the heat into the atmosphere again. That triggers a chain reaction where the energy gets caught in the westerly winds and that propagates downstream toward the United States."

This is a significant finding because it ties climate change, a global event, to local weather events occurring all over the country.

The disrupted weather pattern has effected what Utah winter weather will look like going forward. The winter storms that usually produce our snowpack get broken up before they hit Utah by the stagnant high pressure system in the West. This makes for less frequent and lighter snowfall that gets melted off due to the overall warming of the West. Wang said it is hard to predict exactly what next year is going to look like, but the models have shown this trend for some time.

“You know if you put this year and last year combined they actually fit the story quite well, unfortunately. So there is reason to believe this will be the tendency for the future as well,”Wang said.

Wang is not, however, in the mood to play the “I told you so” game. He wants to move on from the global warming conversation and start preparing people for future extreme weather events caused by climate change.

“Personally, I believe the debate of whether or not we have global warming or we have increased extremes should be done by now,” Wang said. “We should be looking forward. What we should really do is to know the truth and the science behind it. If we know the cause then we can know what the future may look like with better confidence.”

You can find more information on weather patterns and the global temperature report at NOAA.org and at the research page for the Utah Climate Center.