Stratospheric events unlock Northern Europe weather forecasting advances

Stratospheric events unlock Northern Europe weather forecasting advances
by Robert Schreiber
Berlin, Germany (SPX) Mar 19, 2024

Researchers at the LMU Meteorological Institute have identified a stratospheric phenomenon that significantly improves the predictability of long-range weather forecasts in Northern Europe. Long-range weather forecasting, which attempts to predict weather conditions several weeks in advance, is notoriously difficult due to the chaotic nature of weather systems.

Accurate forecasts are crucial for various sectors, including agriculture, renewable energy, and public health, to plan and respond effectively to future conditions. Improvements in these forecasts, even if minor, are therefore highly beneficial.

The LMU team has focused on the impact of the polar vortex-specifically, its weakening or breakdown-on weather patterns. The polar vortex, a strong eastward circumpolar flow in the stratosphere, influences the North Atlantic jetstream and weather over Eurasia. "The state of the polar stratosphere during Northern winter can provide valuable insights for enhancing long-range forecasts, particularly concerning the North Atlantic and Eurasia," stated Thomas Birner, Professor of Theoretical Meteorology at LMU. A current weakening of the polar vortex is expected to affect Eurasian weather in the upcoming weeks, leading to colder conditions but also to a more predictable weather pattern.

In their recent study published in Communications Earth and Environment, the researchers demonstrate that a weakened polar vortex state correlates with a notable decrease in forecast uncertainty for Northern Europe-by approximately 25%. This finding is based on an analysis of forecast ensembles, which typically show greater divergence in longer-term predictions. A reduced spread among these forecasts indicates a higher likelihood of accuracy in predicting weather conditions three to five weeks ahead.

Jonas Spaeth, a doctoral student at LMU and the study's lead author, attributes the reduced uncertainty to the southward shift of the North Atlantic jetstream, which results in fewer winter storms and, consequently, more predictable weather patterns over Northern Europe. This shift, however, increases forecast uncertainty for Southern Europe.

The study not only provides insights into the mechanisms behind forecast uncertainty but also highlights the practical benefits of understanding atmospheric dynamics. "Recognizing how stratospheric conditions affect long-term weather predictions can greatly improve their reliability and usefulness," concludes Spaeth.

Research Report:Stratospheric impact on subseasonal forecast uncertainty in the Northern extratropics