A major SSW event: Arctic stratospheric temperature rises >20°C in days as planetary Rossby waves disrupt the polar vortex. Cold air outbreaks follow 2–4 weeks later.
10 hPa Arctic Temperature
−72°C
Anomaly−28°C
Day of eventDay −20
Vortex stateStrong
Event Timeline
Zonal Wind at 60°N
10 hPa wind+52 m/s
DirectionWesterly
ClassificationPre-SSW
Surface Impact Forecast
Vortex intact. No immediate surface weather impact. Normal winter circulation pattern.
Mechanism: Upward-propagating quasi-stationary Rossby waves (wavenumbers 1–2) break in the stratosphere, depositing westward angular momentum that decelerates the polar night jet. When the jet reverses (easterly), it's a "major SSW" by WMO definition. The stratosphere cools ~6 weeks later as the vortex recovers. The 2021 SSW (Jan 5) led to Texas freeze in Feb 2021.