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The wild January weather across the US is expected to continue this week with forecasts for heavy rain in southern states, after a surge of Arctic air that spilled southward and delivered rare record snowfall to the Gulf Coast last week.
The National Weather Service forecast a storm would pass through the south-western US this weekend with widespread rain and mountain snow.
While the rain would also ease the dry conditions that have fanned devastating fires in southern California, the agency warned of loosened debris and flash flooding if there were heavy falls on hard ground that had been charred.
The warnings follow on the heels of a cold snap in the south-eastern states associated with an elongated polar vortex that allowed the Arctic air to travel to Canada and the contiguous US, said scientists at the National Oceanic and Atmospheric Administration (Noaa).
Usually the jet stream contains the frigid air at the Earth’s northern pole, but when it destabilises and becomes extra “wavy” the cold air can be pushed farther south.
As this frosty air mass met warm moist air fuelled by unusually warm waters from the Gulf of Mexico, a once in a lifetime storm hit the coastal regions and dumped unprecedented levels of snow on Tuesday.
As much as 20cm of snow fell in New Orleans, obliterating the previous record of 6.9cm set in 1963, according to the National Weather Service. Houston was covered by 10cm of snow, the most since 1960.
Florida also reported historic levels of snowfall in the state’s north-western Panhandle, where temperatures plunged well below zero in Tallahassee.
While scientists and climate models have shown that global warming makes extreme weather events more severe — exacerbating hot and dry or wet and cold conditions — they differ on whether human-caused global warming is making the polar vortex weaker and more unstable.
The polar vortex and jet stream are bands of fast-moving air circulating around the Arctic, which play a large role in world weather patterns.
Some studies suggest reduced sea ice cover in the Arctic will result in a weaker vortex, while others show that warming may lead to a strengthened, faster vortex.
Noaa scientist Amy Butler, a polar vortex expert, wrote this week that shifts in the band of air as a result of climate change are likely to be small relative to those of natural variability.
She added that the effect on winter weather would be minor compared with the overall effect of greenhouse gases warming the atmosphere and seas.
The inauguration of Donald Trump as president moved indoors as temperatures in Washington DC dropped to minus 2.7C on Monday, making the ceremony the coldest since Ronald Reagan was sworn-in in 1985 when the thermometer dropped to minus 13.9C.
The executive orders signed within hours of the inauguration included a withdrawal of the US from the 2015 Paris accord, and others halting investments in clean energy secured under former president Joe Biden’s Inflation Reduction Act. These would have a “huge impact” on efforts to curb climate change, the incoming head of the UN COP30 climate talks told the Financial Times.
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