21 Feb 2020 19:09

Vilfand explains extremely warm winter in Russia

MOSCOW. Feb 21 (Interfax) - The unusually warm winter in Russia this year is down to the abnormally wide pressure gap between the Atlantic "weather centers" and an absence of a steady anticyclone over Siberia, the scientific director of the Russian Hydrometeorological Center, Roman Vilfand, told Interfax.

"All circulation rules were broken this year. Practically throughout the winter, for nearly three months, there has been a strong migration eastward of Atlantic air masses travelling so fast that the air was still warm at the point of crossing the Urals into Eastern Siberia. I have not seen anything like that my entire career: that the same air would run the show from the Atlantic [right up] to the Pacific," Vilfand said.

In Europe, weather is mainly defined by processes in two centers above the Atlantic Ocean: near Iceland and above the Azores, he said. Near Iceland, the proximity of the warm Gulf Stream and cold Greenland constantly creates conditions for strong cyclones: quick atmospheric whirlwinds which concentrate a considerable amount of energy and moisture. And to the west of the Gibraltar Strait, off the Azores, is a steady zone of high pressure where normally an anticyclone forms. Interaction between these two weather centers, the Azores anticyclone and the Icelandic cyclone (Icelandic minimum), is crucial for weather forecast.

Warm air from the Atlantic periodically reaches Russia, sometimes moving deep inside the land. However, such situations are extremely rare: first of all, the Atlantic air masses moving eastward normally cool down considerably, and secondly, in Siberia there is yet another constant "weather center," a strong, expansive Eastern Siberian anticyclone, which stops the Atlantic air from advancing into Russia's east, leading to prolonged frosts and fair weather in Siberia, Vilfand said.

This year, both the Atlantic weather centers turned out very polar: the pressure around Iceland was particularly low and the pressure above the Azores was particularly high, which created the conditions for an unusually steady, active air transfer strictly from the west to east, Vilfand said.

Another peculiarity of this year's situation is that the Atlantic air masses, when crossing the Ural mountains, have not met the usual barrier in the form of the East Siberian anticyclone; this moved southward into China, thus clearing the path towards the Pacific for the Atlantic air, Vilfand said.

As a result, Western warmth engulfed not only the European part of Russia, but also the Urals and Siberia. In Yakutia, where winter temperatures would normally be as low as minus 50 degrees Celsius, thermometers showed an unusual minus 15 degrees, and southern Siberian frosts of minus 20 and 30 were replaced by abnormal thaws.

Finally, what ultimately "conserved" the situation is that this winter there was hardly any cold air invasion from the north, the Arctic. The air masses in the cyclone stuck above the Arctic are traveling counterclockwise, from west to east and farther on to north, towards the pole ("a positive phase of Arctic oscillation"). Thus, the icy air is blocked on the pole, unable to reach southern latitudes, Vilfand said. This is a completely normal situation, but in a combination with the other factors it, too, played a part and led to the abnormalities of record scale and duration.

The outgoing winter might turn out the warmest one in Russia on record. Temperatures repeatedly broke all-time highs not only in Moscow but in the Ural and Siberia as well.

It was reported a day earlier that for the first time since records began Muscovites will see in the Fatherland's Defender Day (February 23) without snow: because of the April-style warm weather the remainder of the already thin snow cover will have melted by the weekend. The ground in the European part of Russia is hardly frozen through by late February, river ice in the region is very thin or absent altogether.