Animated forecast of the stratospheric polar vortex at 10 hPa (about 30 km) and 50 hPa (about 20 km): GFS and ECMWF on a polar map or a globe, with the mean wind along 60°N — the number meteorologists use to spot a reversal (a major sudden stratospheric warming). New model runs appear here automatically.
The vortex now — numbers from the latest runs
Latest runs: GFS 3 Nov 06:00 UTC, ECMWF 3 Nov 00:00 UTC.
At the start of the forecast (3 Nov 06:00 UTC) the mean wind along 60°N at 10 hPa is: GFS +3.0 m/s, ECMWF +3.4 m/s.
GFS: the wind drops below zero on 4 Nov 18:00 UTC — a reversal (easterly wind); lowest −2.9 m/s (9 Nov 18:00 UTC).
ECMWF: the wind drops below zero on 5 Nov 12:00 UTC — a reversal (easterly wind); lowest −1.1 m/s (9 Nov 00:00 UTC).
Lower down, at 50 hPa (about 20 km), the weakest wind is: GFS +2.8 m/s, ECMWF +3.0 m/s.
Computed by Weathershot from the latest model runs (forecasts, not observations); they change from run to run. This is not a weather forecast for the ground.
What does it mean?
What is the polar vortex?
In winter, high above the Arctic — about 15 to 50 km up, in the stratosphere — a huge ring of strong west-to-east winds circles the pole, with very cold air trapped inside. This is the stratospheric polar vortex. On the map it is the blue-purple “bowl” over the pole: the lower the 10 hPa surface (about 30 km up), the deeper and stronger the vortex.
What does a “split” mean?
Sometimes waves of air rising from below push the vortex so hard that it breaks into two smaller vortices — for example one over Canada and one over Siberia — or the whole vortex is pushed off the pole. On the map you then see two separate blue patches instead of one.
What does a “reversal” mean?
Meteorologists watch the average wind along 60°N (the dashed circle on the map) at the 10 hPa level. In winter it normally blows from the west at several tens of metres per second. When this average drops below zero — the wind turns easterly — it is called a major sudden stratospheric warming (SSW): the air high above the pole then warms up quickly.
Will it get cold?
Nobody can say yet. After a reversal, the changes can work their way down over the following 2–8 weeks and raise the chance of cold-air outbreaks in Europe, North America or Asia. It is only a higher chance, not a guarantee: after some of these events the weather near the ground changes little, and the cold may go somewhere else. For the next few days, check a regular weather forecast.
Why do GFS and ECMWF differ?
GFS (USA, NOAA) and ECMWF (the European centre) are two different computer models. A few days ahead they usually agree on the broad picture; further out they drift apart. When both show the same thing, the forecast is more trustworthy. Forecasts change from run to run (every 6–12 hours), so always check the run date.
How to read the chart
Solid line: 10 hPa (about 30 km); dashed line: 50 hPa (about 20 km). The red band means easterly wind (a reversal). A dot with a date marks the first reversal in each model. Tap or drag across the chart to move the map in time. In Expert mode you can switch the level, the field (height, temperature, wind) and the colour scale.
For creators
The “For creators” button downloads a frame (16:9, 1:1 or 9:16) with the map, the chart, the run date and a source line, and copies a permanent link to this exact view plus a ready sentence for a video description. You may use the frames — also in monetised videos and posts — as long as the source line stays visible (the ECMWF data licence requires the attribution). Presentation mode hides the buttons and enlarges the text for screen recording.
For creators
Download a frame (16:9, 1:1 or 9:16) or copy a permanent link with the “For creators” button above the map. You may use the frames — also in monetised videos and posts — as long as the source line on the frame stays visible.
Data sources
Data: NOAA GFS 0.25° forecast (public domain).
ECMWF data: this service is based on data and products of the European Centre for Medium-Range Weather Forecasts (ECMWF). Source: www.ecmwf.int. Licence: this ECMWF data is published under a Creative Commons Attribution 4.0 International (CC BY 4.0). Modified: fields resampled by Weathershot from 0.25° to a 0.75° grid, every 6 hours, and quantised. ECMWF does not accept any liability whatsoever for any error or omission in the data, their availability, or for any loss or damage arising from their use, and does not endorse this presentation.
Land outlines: Natural Earth (public domain).