All Weather News

Explaining the Persistent Weather Pattern

19 May 2015, 3:26 pm


In New York City, it didn’t rain a drop for almost three weeks, while up the road in Hartford, Connecticut, the 23-day dry streak was the longest the city had seen in 20 years. In the meantime, Oklahoma City has seen well over a foot of rain in May, San Diego, California is closing in on its rainiest recorded May as the rain continues to drench areas that have already been inundated for much of the past month.

The weather for much of the country has been stubbornly persistent, whether it be extra sunshine, heat, rain or cooler temperatures. Severe weather has been largely concentrated in the southern part of the plains, particularly in Oklahoma and Texas. While that in it of itself isn’t especially unusual, the regularity of severe weather and the flooding rainfall accompanying the storms has been. Meanwhile, in Charlotte, North Carolina a drop of rain hadn’t been recorded in the month of May as of Tuesday afternoon.

So what’s causing all of this especially persistently weather? The explanation starts at the upper levels of the atmosphere, where the jet stream, a band of fast-moving winds that play a critical role in determining weather, has been located in mostly the same general vicinity all month long. A strong area of high pressure in western Canada has forced the jet stream to shoot south, creating a trough, or elongated area of low pressure (see map). When it moves back up across the northeast, it creates warmer, drier conditions under a ridge of high pressure. That same pattern has been in place for the last several weeks, and there’s little indication of that changing over the next few days.

For the forseeable future, it appears the rough pattern will stay in place. Another unusually cool area of low pressure moves south into California later this week, eventually spinning east into the Great Basin and through Utah and Colorado, bringing more cool rain with it to those states before triggering severe weather again across parts of the Plains this weekend. So get ready for…more of the same.

Meteorologist Chris Bianchi

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