Looks like Central and Eastern US riders will get a chance to stress test their heated gloves. And I'll get a chance to test my rain gear and hone my wet weather riding skills.
Abstract: An extraordinary atmospheric planetary wave (#1) (1st picture), over 30 miles high, covering earth's entire Northern hemisphere, will break over the North Pole on Xmas day. This wave, which will transfer tremendous amounts of heat to the upper stratosphere, is likely to split the polar vortex in two. This will likely drive cold air out of the Arctic towards the Central and Eastern US in January and February.
Details: The winter night that starts over the North Pole in September causes a deep vortex to form around the North Pole in early fall. By the 18th of December this year, the planet circling "storm in the stratosphere" was extraordinarily cold -115 F (-82 C) and winds today are as high as 220 mph (355 km/h) in the upper stratosphere where the atmospheric pressure is 1% of surface pressure (10mb). This monster storm that develops every fall above the weather layer has become more intense in the fall months with human-caused global warming and ozone loss. This year has been no exception. However, as the polar vortex has become more intense in the Fall it has also become more unstable in the Winter months.
When the spin of the jet stream in the lower atmosphere (the troposphere) aligns with the spin in the polar vortex in the layer above, the stratosphere, as it does in the long polar winter, large amounts of wave energy may be transferred upwards. The most powerful planetary wave is typically #1 which encircles the Northern hemisphere diving South over the Pacific Ocean and pushing polewards over the Atlantic. When this wave intensifies, it not only drives heat towards the pole on the Atlantic side, it also drives wave energy upwards from the troposphere to the upper stratosphere. This upwards wave breaks at the boundary of the stratosphere with layer above it, the mesosphere. These upwards breaking waves generate large amounts of heat and put a brake on the winds at the top of the stratosphere.
The dome of heated air that is formed spins clockwise, like a surface high pressure area, and disrupts the Westerly flow of the storm-like vortex below it. The slowing and heating of the polar vortex in the upper stratosphere works its way to lower levels by this process of vortex disruption. In strong stratospheric warming events the vortex disruption may work its way down to affect polar surface weather over the winter months. Strong events usually happen in January and February. The period around Xmas is very early for a major stratospheric warming, but both the American and European models now predict it will happen. The models indicate that there is a good chance that the polar vortex will be split in two by the intense warming.
When the polar vortex disruption reaches the lower atmosphere it tends to increase the surface pressure over the North Pole and Arctic Ocean. In particular, the Beaufort High, that is located north of Alaska over the Beaufort sea, intensifies and the flow of cold air out of the Arctic east of the Rocky mountains intensifies. The flow of cold air towards western Europe may also intensify like it did late last winter when "the Beast from the East" brought bitterly cold Siberian air to Western Europe. This year, the American Climate Forecast System (CFS) model forecasts that the Eastern US will be colder than normal, but not Western Europe. It forecasts that a cold flow out of the north polar region will bring brutal cold to Northern Siberia and Scandinavia in mid-January, but not Western Europe. Time will tell. The model cannot be depended on to predict details accurately. What is clear is that the Eastern half of the US is likely to be significantly colder than normal in mid-January. This forecast for mid-January is consistent with what happened after major stratospheric warmings in El Nino years like this one (2nd picture).
Climate change may be amplifying the impacts of El Nino events and major stratospheric warmings. Large areas of the Barents Sea, which used to be covered by ice and a fresh water layer, is now an extension of the North Atlantic. This region can now transfer huge amounts of heat from the ocean to the atmosphere amplifying planetary wave #1 near the pole. Likewise, the increase in ocean heat in the North Pacific, particularly in El Nino years, increases the amplitude of planetary wave #1. This may be destabilizing the polar vortex in mid-winter leading to more extreme weather and increased variability in winter weather.
The good news in this combination of a sudden stratospheric warming and El Nino is that California is likely to have a wet January as the storm track gets pushed south by likely blocking high pressure areas over Alaska. This weather pattern could extend into February, but the model becomes less accurate over time. The impact of major stratospheric warmings can continue for several months while vortex disruptions work down "like dripping paint" from the stratosphere into the weather. The cold weather in the Eastern US and warm weather in Alaska will probably continue into February. California is likely to have a wetter than normal period from January through March.
The CFS model prediction of wet weather for California is consistent with similar situations but the prediction of a dry East Coast is not consistent with the historic record. Historically, heavy snow events have happened on the East Coast following sudden stratospheric warmings. Cold air may dam up over Eastern Canada and storms may track up the East Coast delivering large amounts of snow to the mid-Atlantic and Northeast if this winter follows historic patterns. Time will tell.
Topic: Winter (Read 11917 times)