At German climate and weather site wobleibtdieerderwaerumund.de here, author “Schneefan” writes about the Arctic stratosphere and potential polar vortices blasting into Europe before winter makes an exit.
He writes that models had calculated a warming of the stratosphere over parts of the Arctic, and this is now indeed taking place. And that warming has been strong and rapid. What does such an upper atmosphere warming mean? Schneefan writes it leads to a disturbed polar circulation, which leads us “to expect additional cold surprises over the earth’s northern hemisphere“.
GFS analysis of temperatures in the lower stratosphere at 16 km altitude (100 hPa). Over Canada the air has warmed strongly. Source: www.cpc.ncep.noaa.gov/products/stratosphere/mct.
Moreover at the upper stratosphere at about 30 km elevation (10 hPa) the rash warming has been interrupted, as the following chart depicts:
NOAA/CPC analysis of temperatures over the Arctic (90N – 65 N) in the upper stratosphere at 10 hPa (approx. 30 km altitude). DOY=Day Of Year. Source: www.cpc.ncep.noaa.gov/products/stratosphere/.
The interrupted upper stratosphere warming eventually led to the interruption working its way down to the lower stratosphere 18 km altitude (70 hPa) just a bit later:
NOAA/CPC analysis of temperatures in the lower stratosphere at 70 hPa (about 18 km altitude). After a minor warming cooling has since taken over(DOY=Day Of Year). Source: www.cpc.ncep.noaa.gov/products/stratosphere/.
This warming of the stratosphere over the Arctic leads to a negative Arctic Oscillation (AO), Schneefan writes, which in turn leads to polar vortices plowing down into the middle latitudes, as was the case in mid January, 2016.
NOAA prognosis (red line in the upper chart) for the Arctic Oscillation (AO) dated February 5, 2016, for the upcoming two weeks. The black line shows a drop into the negative range in mid February – down to -2, That would mean a strong polar vortex. Source: www.cpc.ncep.noaa.gov/shtml.
Yet the prognosis for the North Atlantic Oscillation (NAO) – contrary to the the (cold) values seen in January – remains slightly in the positive range, which would point to mild weather just ahead for Western and Central Europe:
NOAA prognosis for the North Atlantic Oscillation (NAO) from February 5, 2016, for the upcoming 2 weeks. The values are expected to remain in the positive range, which would mean mild westerly winds persisting. Source: www.cpc.ncep.noaa.gov/products/precip/shtml.
However stratospheric prognoses point to a continued tendency toward a major warming/SSW) already in just a few days, which would mean that in 3 to 10 days colder weather for Western and Central Europe:
ECMWF prognosis of 5 February 2016 for pressure and temperature of the upper stratosphere 10 hPa (approx. 30 km elevation) for 8 February 2016. The cold polar vortex is positioned over eastern Greenland. The cold pole of the northern hemisphere is over Scotland (C=Cold). The cold pole is set to shift over Europe. Source: www.geo.fu-berlin.de/met/ag/strat/produktehtml.
Such major warmings of the stratosphere last happened in 2012 and 2013 – in January, after which a very cold February followed in 2012, and an historically severe cold March gripped Europe in 2013 respectively.
Cold February of 2012. Source: www.esrl.noaa.gov/.
Historic cold March of 2013. Source: www.esrl.noaa.gov/.
So, Schneefan writes, Europeans should not be writing off the winter just yet, as many meteorologists seem to have been doing over the past week or so. Weather is always a big bag filled with surprises. Things can go from mild to brutally cold awfully quickly.