Scientists Say Weak Polar Vortex Makes Weather More Predictable in Northern Europe

Meteorological phenomena in the stratosphere are making long-term weather forecasting in northern Europe easier, according to new research. Find out more here!

polar vortex: cyclone, Europe.
Apparently, polar vortex oscillations have an influence on long-term forecasts. Whether positive or negative.

Weather is a chaotic system and predicting weather conditions several weeks in advance is a considerable challenge. The accuracy of these long-term forecasts remains generally quite low. Therefore, even small improvements can be valuable across multiple industries. Should we be "afraid" of the polar vortex or the sudden warming of the stratosphere in winter? Scientists from Ludwig Maximilian University(LMU) in Munique are investigating a phenomenon that originates in the stratosphere - the layer of our atmosphere located between 15 and 50 kilometres in altitude.

"Previous work has shown that during the Northern Hemisphere winter, the state of the circulation in the polar stratosphere can provide useful information to improve long-term forecasts, especially for the climate in the North Atlantic and Eurasia." Thomas Birner, professor of Theoretical Meteorology at LMU and one of the study's authors.

In particular, when the polar vortex (a band of strong eastward circumpolar flow at stratospheric levels) weakens or breaks up, the North Atlantic jet stream tends to shift southward and increases the likelihood of cold spells and waves over Eurasia.

Rupture of the stratospheric vortex and a possible colder but less chaotic climate

LMU meteorologists highlighted an additional aspect of the stratosphere's influence on long-term weather forecasts: weak polar vortex states, such as the one currently prevailing, are typically followed by reduced uncertainty in 3- to 5-week forecasts over northern Europe.

The authors found that forecast sets show a reduced range of possible weather conditions by about 25%. These ensembles are composed of a large number of individual forecasts, which typically diverge over longer forecast periods.

Following the weak polar vortex, these forecasts are less widespread in Northern Europe, which makes the weather more predictable. "We attribute this reduction in forecast uncertainty to the southward shift of the North Atlantic jet stream," says Jonas Spaeth, PhD student at the LMU Institute of Meteorology and lead author of the new study.

On the other hand, forecast uncertainty increases in southern Europe.

The consequent southward shift of winter storm trajectories, which are the main source of forecast uncertainty this season, leads to less storm activity, thus reducing forecast uncertainty in northern Europe. In contrast, forecast uncertainty increases in southern Europe.

Reference of the news:
Spaeth, J., Rupp, P., Garny, H. et al. Stratospheric impact on subseasonal forecast uncertainty in the northern extratropics. Communications Earth & Environment (2024).