In 10 days all meteorological models forecast a titanic warming of the stratosphere over northeast Canada, Greenland to the north of Europe. The event evolves quickly and qualifies as a “sudden stratospheric warming” or SSW. Stratospheric warming events in the polar region during wintertime are the primary drivers of arctic air evolution at ground level as the weather atmosphere (troposphere) contracts and cools beneath the weight of the warming and expanding stratosphere above. This set of circumstances occurred just-before Christmas and lead to the U.S. arctic outbreaks that followed.
However, like many climate regimes in the earth’s modern-day environment not all previously well-understood events react the same regarding the attendant sensible weather. The stratospheric warming event projected for Valentine’s Day 2018 is the next example.
The European Ensemble is used to identify the warming stratosphere in 10+ days (Fig. 1). Note the strength of the warm anomaly in the polar region, easily the strongest of winter 2017-18 and much stronger than the warming episode near the North Pole in December which lead to the U.S. arctic outbreak. The troposphere responds with a cold polar vortex beneath the stratospheric warming (Fig. 2). But! Note where this event is taking place…over the open ocean well north of northwest Europe (Fig. 3). The process by which stratospheric warming cause arctic air evolution in the northern latitudes – normally over vast areas of snow cover – is substantially weakened as the event takes place across open/ice free ocean.
In the modern climate era this part of the far northern portion of North Atlantic is typically not covered with ice due to the warming of the polar atmosphere caused by increased CO2. Due to the stratospheric warming event taking place over the open ocean of the far northern portion of the North Atlantic a massive arctic outbreak normally caused by SSW events is not likely to occur.
Fig. 1: The ECM ensemble stratospheric (10 MB) temperature anomaly forecast valid February 12th. Charts provided by CWG/Storm Vista.
Fig. 2: The ECM ensemble middle troposphere (500 MB) trough/ridge forecast identifies a strong polar vortex beneath the stratospheric warming near Iceland on February 12th. Charts provided by CWG/Storm Vista.
Fig. 3: Northern hemisphere snow cover and ice cover analysis provided by NOAA.