The Arctic is refreezing fast. Trend lines that were way below all other years for weeks on end have returned to the pack, as can be seen on the Daily graphs page of the Arctic Sea Ice Graphs website. Of course, there's still much more open water now than during the long-term average, and so we start looking for signs of weird or WACC-y weather, anomalous snowfall on the Northern Hemisphere land masses, outbreaks of cold air, atmospheric blocking patterns...
Here's something I don't remember seeing often in the past 3 years:
That's the latest surface pressure map from the Danish Meteorological Institute. It looks pretty impressive. The red and yellow are high pressure areas, meaning clear skies, low temperatures and fast freezing. These huge high pressure areas have caused the Arctic Oscillation index to go way down into negative territory:
In the meantime, south of the Arctic, a hurricane called Sandy is wreaking some havoc in the Caribbean. Sandy is projected to move northwards along the US east coast. Some weather models forecast a potential landfall in the Mid-Atlantic or New England that could cause a large amount of damage:
What could be weird is this: Apparently those huge high pressure areas in the Arctic can potentially cause Sandy to veer off towards the US. To quote this wonderfully informative piece on Climate Central (hat-tip idunno):
During the past 24 hours, the models have come into better agreement about how Sandy will interact with several unusual weather features. Those converging events include a large dip in the jet stream into the eastern U.S., a powerful subtropical jet stream moving across the southern U.S., a massive area of high pressure that will be parked over northeastern Canada and southwestern Greenland, and a storm in the Central Atlantic. These features may help steer Sandy right into the Mid-Atlantic or New England.
The high pressure area near Greenland, in particular, may act as a block (it's technically known as as a “blocking high”), which may help prevent Sandy from moving out into the open ocean. While it is not unusual to have a high pressure area in that location, its intensity is striking for this time of year. As Jason Samenow of the Capital Weather Gang wrote, the North Atlantic Oscillation, which helps measure this blocking flow, "is forecast to be three standard deviations from the average — meaning this is an exceptional situation."
Recent studies have shown that blocking patterns have appeared with greater frequency and intensity in recent years, which some scientists think may be related to the loss of Arctic sea ice as a result of global warming. The 2012 sea ice melt season, which just ended one month ago, was extreme, with sea ice extent, volume, and other measures all hitting record lows. The loss of sea ice opens up large expanses of open water, which absorbs more of the incoming solar radiation and adds heat and moisture to the atmosphere, thereby helping to alter weather patterns. Exactly how weather patterns are changing as a result, however, is a subject of active research.
What a coincidence, eh? I need another crash course on interpreting weather maps. And let's hope Sandy either doesn't develop into a massive storm, or doesn't make landfall. But this could be one for the weird category.