Blocking patterns, climate change, and increasing big weather events

Hurricane Sandy broke records as it slammed into New Jersey this week. The number of those killed creeps toward 100 as the damage estimate nears $100 Billion. But why hasn’t New Jersey been struck by a hurricane in generations? Typically, hurricanes are thrown out to sea by a strong jet stream that moves west to east across the Eastern Seaboard. However, as Sandy moved northward from Cuba, it encountered a large, expansive high pressure system over Eastern Canada. With a low pressure system sitting east of Bermuda, there was only one thing for the hurricane to do: turn left.

We are so fortunate to have a network of reliable computer models. There’s no way to know how many lives the  investment in these models saved. The ECMWF model had Sandy making this left turn about 5 days in advance! While Meteorologists scratched their heads saying “That’s not possible!” it became apparent that the blocking high pressure would cause Sandy to make that left turn…something no other hurricane had done before!

If you’ve been watching national news coverage of the aftermath of the storm, you’ve probably picked up on several reporters and pundits linking this storm to climate change. Before I dive into this topic, let me take you back several years ago when I had the opportunity to attend a climate change conference. Stu Ostro, Senior Meteorologist with The Weather Channel, gave a fascinating talk about global warming…more specifically, United States warming. It was then that I was sold on the fact it was occurring. What did it? He showed a simple bar graph of the increasing record highs being observed. He then showed a decreasing number of record lows being observed. Note: He was a skeptic of climate change until he began studying it. And Stu has since written several articles linking big, long-term blocking patterns to significant weather events.

It’s no secret this summer was one of the driest on record for the Central U.S. This was caused by a pattern that blocked significant areas of low pressure from moving west to east across the Central United States. And the same thing happened with Sandy. The pressures bombed out within the storm as it interacted with cold air moving into the Eastern Seaboard causing the system to intensify and spread out, affecting an area 1,000 miles across.

The lesson that should be learned about the affect climate change is having on weather pattern is higher variability! Some climate scientists believe this is due to the loss of Arctic Sea Ice. However, climate change is introducing more chaos into our weather patterns. The droughts are drier, the arctic outbreaks are colder, the high pressure systems are more expansive (and blocking), and the low pressure systems (hurricanes) act erratically due to different steering currents of air.

In the past five years, we have been learning more about the blocking pattern called the “Greenland Block” (also called a negative NAO-North Atlantic Oscillation). This is when a dominant area of warm, high pressure sets up over Greenland and the Canadian Maritimes. This causes cool, Canadian air to move down from Northwest Canada into the Great Lakes States. As the jet moves back north, an active stormtrack exists from the Ohio Valley into Ontario. If this blocking pattern materializes, it can last for several weeks to a month! Conversely, the oscillation can go positive, causing a large ridge to reside over the Central United States (which was the culprit for several nearly snow-less winters, including 2011/2012).

And we are just beginning to learn more about how the Pacific Oscillation of the jet stream is able to modify our long-term weather. The strength and placement of the jet over Alaska is being linked to how persistent the trough is over the Central United States (and vice versa: how it relates to a ridge should the Greenland block go into positive phase).

The important bottom line is we’re in a learning mode when it comes to climate change and its effects on weather patterns. The good news is that knowledge levels are increasing and weather modeling is getting better. The bad news is the fact that big weather events are occurring more frequently, and it doesn’t look like it’s going to slow down anytime soon. -Eric

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Posted under 13 Climate Authority, climate/climate change, tropical weather

This post was written by qni_it on November 1, 2012

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