First Grímsvötn volcano erupted through a glacier. Then it exploded through the air. Finally, its debris changed the atmosphere so much that it blasted winter away from most of the US.
Most people don’t even know anything about Grímsvötn. It blew up in the middle of Iceland last May. Ash and chemicals roared 12 miles high into the air. Then everyone discovered that its ash was too high to mess with air travel to Europe and forgot about it. Unfortunately, the ash and chemicals are still lingering in the air, even if no one cares. They block out sunlight in parts of the Arctic. The air cools. Air pressures change.
What has happened is as simple as 1, 2, and 3.
- Winds really make a difference in winter. They can blow Arctic air deep into North America or away from the US.
- Air pressure determines where the winds blow. In the North Atlantic, the low pressure near Iceland (called the Icelandic low) steers the winds.
- The volcano in Iceland changed the air pressure over Iceland. The Icelandic low became very low.
Last week’s blog The NAO: The Crossing Guard of the Atlantic discussed a weather pattern called the North Atlantic Oscillation (NAO). When the cold Icelandic low is very different from the warm high air pressure in the mid-Atlantic, the Azores High, winds trap the cold Arctic air in the north. This is called a positive NAO and this winter the NAO was more positive than it has been in a century.
The Icelandic Low is so strong that it has created a positive NAO. Source: NOAA
Even now, the NAO is shifting between neutral and positive. It sometimes allows cold air to hit the US, and then it zips it out into the Atlantic. The cold doesn’t stay very long.
It doesn’t mean that it doesn’t get cold. A huge storm from Siberia, “The Beast from the East”, has hit Europe. China has shivered with temperatures below normal since January. Two cold spells plunged down and killed people in India.
Still the cold winter has avoided most of the US. The blast of Grímsvötn, a volcano in Iceland, has warped the normal Arctic winds. In the process, it warmed the US. If you are seeing flowers in February, point to the volcano!
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin  and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.