Wobbling jet stream gets blame for weather havoc
Scientists disagree on what causes stormy hot, cold extremes
WASHINGTON — The jet stream, a river of air that generally dictates the weather, usually rushes rapidly from west to east in a mostly straight direction.
But lately it seems to be wobbling like a drunken driver, wreaking havoc as it goes. The more the jet stream undulates north and south, the more changeable and extreme the weather.
The most recent example occurred in mid-June when some towns in Alaska hit record highs. McGrath recorded an all-time high of 94 degrees on June 17. A few weeks earlier, the same spot was 15 degrees, the coldest recorded for so late in the year.
You can blame the heat wave on a large northward bulge in the jet stream, Rutgers University climate scientist Jennifer Francis said.
Several scientists are blaming high and low extremes on a jet stream that is not quite playing by its old rules. Some say it’s related to global warming, but others say it’s not.
Upside-down weather also happened in May. Early California wildfires fueled by heat contrasted with more than a foot of snow in Minnesota. Seattle was the hottest spot in the nation one day, and Maine and Edmonton, Canada, were warmer than Miami and Phoenix.
Consider the follwing unusual occurrences over the past few years:
The winter of 2011-12 had little snow, with record warmth in March. That was followed by the winter of 2012-13, when nor’easters struck the same coastal areas repeatedly.
Superstorm Sandy took an odd left turn in October from the Atlantic straight into New Jersey, something that happens once every 700 years or so.
One 12-month period had a record number of tornadoes, then 12 months that set a record for a lack of tornadoes.
And, in what weather officials call a “spring paradox,” the United States had an unusually large area of snow cover in March and April and a near-record low area of snow cover in May. The entire Northern Hemisphere had record snow coverage area in December but the third-lowest snow extent for May.
The polar jet stream affects the Northern Hemisphere. It dips down from Alaska, across the United States or Canada, then across the Atlantic and over Europe.
It all starts with the difference between cold temperatures in the Arctic and warmer temperatures in the midlatitudes, Francis said. The bigger the temperature difference, the stronger the jet stream, the faster it moves and the straighter it flows.