Long-range winter weather forecasts could be twice as accurate by taking account of unusual winds miles up in the stratosphere,

Long-range winter weather forecasts could be twice as accurate by taking account of unusual winds miles up in the stratosphere, scientists have found.

High up in the stratosphere is the polar night jet stream, at around 40km (25 miles) above the surface of the Earth -- around the height reached by record-breaking parachutist Felix Baumgartner.

Winds in the polar night jet stream usually blow from the west and have speeds of around 70mph. The research team found that during conditions in which the polar night jet stream wind speeds exceed 90mph, or reverse their direction to flow from the east, forecasts in both the stratosphere and troposphere (the layer of atmosphere closest to the ground), are more skillful.

While it was previously known that a sudden weakening of these winds, and subsequent warming of the stratosphere, was a source of predictability, the researchers found that the opposite was also true when the polar night jet stream strengthened and the polar stratosphere was unusually cold. Such stratospheric conditions occur up to 3-4 times a winter, meaning that around one in five winter 'sub-seasonal' forecasts (those looking 2-4 weeks ahead) might benefit from this effect.

The strength of stratospheric winds can influence the position of the jet stream in the troposphere, having a major influence on weather across the North Atlantic, and allow freezing polar air to travel further south than would normally be expected.

Citation: 

Institute of Physics. "Forecasters look higher for clues to winter weather: Long-range winter weather forecasts could be twice as accurate by taking account of unusual winds miles up in the stratosphere, scientists have found." ScienceDaily. ScienceDaily, 13 October 2015. <www.sciencedaily.com/releases/2015/10/151013102413.htm>.