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Siberian Express makes it's way to the US

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The first arctic outbreak of the winter season is plunging across the Lower 48 this weekend, causing widespread freezing temperatures and record breaking lows.

Thursday morning lows in Casper, Wyoming saw the mercury dip to negative 33 degrees. That set a record for the coldest reading in Casper since February 16, 2006, according to the National Weather Service. In Denver, Colorado, morning lows were a spine chilling negative 10 degrees, just a few degrees short of the record.

Temperatures this weekend are expected to drop a good 10 to 30 degrees below normal in many locations. That means more record lows are expected to be broken as this Siberian airmass moves South through the United States.

KFOX 14 Meteorologist Zach Covey says the arctic outbreak originated in Siberia a few weeks back. The upper atmosphere saw the airmass travel North, through the North Pole before plunging down through Canada on it's way to the United States.

"It's all due to the Omega Block, out in Alaska", Covey says. "If we look at the 500mb height surface, which is the middle portion of the atmosphere, we can examine how that pressure surface will change over time. It's average height is around 18,000 feet up into the atmosphere. As the 500mb layer warms, the heights will rise even higher than that 18,000 ft, and that's what can cause a strong Southerly component to the winds. On either side of that rising ridge of high pressure, we can find equally strong low pressures. This forces the jet stream, a column of fast moving air, to bend like up and around the highs and lows, in a way that resembles the Greek letter 'Omega'. This means a strong Northerly component to the winds occurs just to the East of that block in Alaska, forcing the Siberian Airmass to surge South into the Lower 48", says Covey.

But as the Nation braces for this chilly outbreak this weekend, Covey says to get ready for another, even colder blast, next week. "If you think this is cold, just wait for millions of American's to experience sub-freezing temperatures by late next week. Winter is here to say."


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