The polar vortex, day by day
Height of the 10 hPa surface (GEFS control, from the analysis to 16 days): the blue trough is the vortex, the white line its edge, the particles follow the wind.
- Low height: vortex core
- High height: stratospheric anticyclone
- Vortex edge
Globe: GEFS control member (NOAA), Oct 29, 2026 00 UTC run, geopotential height and wind at 10 hPa north of 20° N; the thickness of the stratosphere is exaggerated. Slider: day shown.
The claim against the data
The claim shared on social media on 29–30 October 2026 makes four points: the vortex could break down by 17 November; it would be one of the earliest sudden warmings since 1959; blocking highs over Alaska and the Urals would cause it, through a wave-number-2 pattern; surface effects (cold, blocking, snow) would follow from late November into December. Each row below is recomputed with every new analysis and every new run.
| Claim | What the data show | Verdict |
|---|---|---|
| Vortex breakdown by 17 November | GEOS deterministic forecast (NASA): lowest wind −5.0 m/s on Nov 7, 2026 (forecast to Nov 7, 2026). GEFS ensemble of Oct 29, 2026: 29 of 31 members turn easterly on at least one day, between Nov 3, 2026 and Nov 11, 2026; the probability peaks at 81 % on Nov 4, 2026. The median stays below 10 m/s to the end of the forecast (Nov 14, 2026): no quick rebuilding of the vortex in sight. | Likely |
| One of the earliest warmings since 1959 | The earliest known major warming is that of Nov 27, 1968 (NOAA compendium, reanalyses since 1958); since 1979, in the NASA data, Dec 3, 1981. A reversal in early November would thus be about three weeks ahead of any precedent. The wind was 15.8 m/s at the last complete analysis (within the normal range for the date); in the GEOS forecast it falls below the 1979–2026 minimum of the date on 8 day(s). | True, if the reversal happens |
| Blocking over Alaska and the Urals, wave number 2 | The heat flux of the waves entering the stratosphere (45–75° N, 100 hPa) is 25.5 K·m/s on Oct 27, 2026 (among the highest 10 % for the date) and, in the GEOS forecast, reaches 29.0 K·m/s on Oct 31, 2026, above the highest value for the date since 1979 on 6 day(s). This is the forcing that slows the vortex down (Polvani and Waugh, 2004). In the GEFS control, wave 2 dominates wave 1 at 10 hPa from Oct 29, 2026 to Nov 4, 2026 (up to 611 m amplitude at 60° N) and the vortex stretches to an aspect ratio of 3.2: the shape of an incipient split. Ridges at 500 hPa along 60° N over the first week (GEFS control): Scandinavia and North Sea (3° E, +357 m), western Canada (111° W, +134 m). | Partly confirmed |
| Cold, blocking and snow in late November and December | After the 42 major warmings from 1958 to 2023, the daily NAO from day +5 to +60 averages −0.17 (p = 0.003 against random dates), negative on 67 % of the days; cold days in northern Europe are 1.34 times as frequent (p = 0.032). A real effect on average, but slow, and missing for about a third of the events (full test). | Plausible, not certain |
A forecast beyond 10 days remains a probability. A major warming is defined by the easterly reversal of the mean wind at 60° N and 10 hPa: a very weak or displaced vortex that does not reverse does not count, even if its effects can be similar.
Show the data as a table
Show the data as a table
Show the data as a table
Show the data as a table
Show the data as a table
Shape of the vortex at 10 hPa, GEFS control of Oct 29, 2026
Polar maps of the height of the 10 hPa surface (pole at the centre, Greenwich meridian pointing down), with the vortex edge in white and its centroid (cross). The shape is measured by the moments of the height (Matthewman et al., 2009; Seviour et al., 2013): an aspect ratio above 2.4 marks a split into two vortices, a centroid south of 66° N a displacement. The amplitudes of waves 1 and 2 at 60° N tell which of the two shapes dominates.
ratio 2.6, centroid 85° N; waves 1 and 2: 377 and 510 m Split
ratio 3.1, centroid 83° N; waves 1 and 2: 425 and 588 m Split
ratio 2.0, centroid 77° N; waves 1 and 2: 454 and 329 m Centred
ratio 2.0, centroid 74° N; waves 1 and 2: 446 and 194 m Centred
ratio 1.8, centroid 70° N; waves 1 and 2: 548 and 110 m Centred
| Day | 29 Oct | 31 Oct | 2 Nov | 4 Nov | 6 Nov | 8 Nov | 10 Nov | 12 Nov | 14 Nov |
|---|---|---|---|---|---|---|---|---|---|
| Split | 100 % | 100 % | 100 % | 77 % | 0 % | 0 % | 0 % | 0 % | 0 % |
| Displaced | 0 % | 0 % | 0 % | 0 % | 0 % | 0 % | 0 % | 0 % | 0 % |
| Centred | 0 % | 0 % | 0 % | 23 % | 100 % | 100 % | 100 % | 100 % | 100 % |
Ridges and blocking at 500 hPa, first week
Departure of the 500 hPa height (about 5.5 km) from its latitude mean, averaged from Oct 29, 2026 to Nov 5, 2026 (GEFS control): ridges and blocking highs in red, troughs in blue. These structures, when they sit at favourable longitudes, send waves 1 and 2 up into the stratosphere.
From the top down: does the anomaly descend?
Standardised anomaly of the wind at 60° N from 10 to 150 hPa since 1 September (departure from the mean of the date divided by the standard deviation implied by the 10th and 90th percentiles). After a warming, the weakening of the vortex often descends to the tropopause within two to three weeks, then influences surface weather for one to two months (Baldwin and Dunkerton, 2001; Kidston et al., 2015).
33 major sudden stratospheric warmings since 1979
Detection after Charlton and Polvani (2007), as in the NOAA compendium (Butler et al., 2017): first day of easterly wind at 60° N and 10 hPa between November and March, 20 consecutive westerly days since the previous event, return of westerlies for 10 days before 30 April (otherwise it is the spring final warming). Of 33 events found in the NASA data, 28 are in the compendium within three days; 3 are marginal (a single day barely below zero).
| Onset (easterly wind) | Lowest wind | Easterly days | Polar-cap warming | NOAA compendium (ERA5) |
|---|---|---|---|---|
| Mar 3, 2026 | −7.3 m/s | 6 | +8.9 K | after its last update (2023) |
| Mar 3, 2024 | −20.7 m/s | 21 | +17.7 K | after its last update (2023) |
| Jan 15, 2024 | −2.0 m/s | 2 | +19.7 K | after its last update (2023) |
| Feb 15, 2023 | −13.6 m/s | 5 | +24.4 K | Feb 15, 2023 |
| Jan 4, 2021 | −6.5 m/s | 5 | +28.1 K | Jan 4, 2021 |
| Jan 1, 2019 | −10.2 m/s | 17 | +26.0 K | Dec 31, 2018 |
| Feb 11, 2018 | −24.2 m/s | 17 | +32.2 K | Feb 11, 2018 |
| Jan 31, 2017 marginal | −0.1 m/s | 1 | +33.6 K | absent |
| Jan 5, 2013 | −13.3 m/s | 22 | +32.2 K | Jan 5, 2013 |
| Mar 23, 2010 | −2.9 m/s | 3 | +5.8 K | Mar 23, 2010 |
| Feb 8, 2010 | −6.7 m/s | 3 | +28.4 K | Feb 8, 2010 |
| Jan 23, 2009 | −31.1 m/s | 30 | +51.2 K | Jan 23, 2009 |
| Feb 21, 2008 | −15.0 m/s | 7 | +18.3 K | Feb 21, 2008 |
| Feb 23, 2007 | −8.8 m/s | 4 | +16.0 K | Feb 23, 2007 |
| Jan 20, 2006 | −26.4 m/s | 19 | +26.8 K | Jan 20, 2006 |
| Jan 4, 2004 | −15.1 m/s | 10 | +25.1 K | Jan 4, 2004 |
| Jan 17, 2003 | −2.7 m/s | 1 | +17.1 K | Jan 17, 2003 |
| Dec 29, 2001 | −2.0 m/s | 4 | +31.9 K | Dec 29, 2001 |
| Feb 10, 2001 | −2.0 m/s | 3 | +26.8 K | Feb 10, 2001 |
| Mar 19, 2000 | −3.4 m/s | 3 | +18.0 K | Mar 19, 2000 |
| Feb 25, 1999 | −17.5 m/s | 21 | +37.0 K | Feb 25, 1999 |
| Dec 14, 1998 | −22.5 m/s | 6 | +33.2 K | Dec 14, 1998 |
| Feb 4, 1995 marginal | −0.0 m/s | 1 | +34.0 K | absent |
| Feb 20, 1989 | −13.9 m/s | 9 | +26.2 K | Feb 20, 1989 |
| Mar 13, 1988 | −4.1 m/s | 3 | +32.2 K | Mar 13, 1988 |
| Dec 7, 1987 | −18.1 m/s | 9 | +25.1 K | Dec 7, 1987 |
| Jan 22, 1987 | −13.4 m/s | 5 | +20.9 K | Jan 22, 1987 |
| Dec 31, 1984 | −15.8 m/s | 5 | +31.1 K | Dec 31, 1984 |
| Feb 23, 1984 | −12.0 m/s | 4 | +32.9 K | Feb 23, 1984 |
| Dec 3, 1981 | −2.4 m/s | 2 | +1.1 K | Dec 3, 1981 |
| Mar 3, 1981 marginal | −0.1 m/s | 1 | +-12.4 K | Mar 3, 1981 |
| Feb 29, 1980 | −7.3 m/s | 2 | +35.4 K | Feb 28, 1980 |
| Feb 21, 1979 | −16.4 m/s | 8 | +12.6 K | Feb 21, 1979 |
Polar-cap warming: highest 10 hPa temperature (60–90° N) from 10 days before to 10 days after the onset (the air often warms before the wind turns), minus the mean of days −30 to −20. The compendium stops in February 2023; the events of January and March 2024 and March 2026 come from the NASA data alone.
Show the data as a table
And at the surface? What past warmings show
Correspondence test of the Observatory on the 42 major warmings of the compendium (1958–2023): daily NAO (NOAA CPC) and mean temperature of European cities (ERA5), anomalies from day +5 to +60 after each event, against random dates of the same season. Cold days are those below the 10th percentile of December to March.
| Response | Mean, days +5 to +60 | p | Cold days |
|---|---|---|---|
| NAO | −0.17 (67 % of negative days) | 0.003 | — |
| North-east Europe (Moscow) | −0.44 °C | 0.204 | × 1.34 (p = 0.032) |
| South (Madrid, Rome) | −0.15 °C | 0.294 | × 1.11 (p = 0.240) |
| North-west (London, Paris, Berlin) | −0.32 °C | 0.122 | × 1.19 (p = 0.165) |
Data. Annual meteorological statistics of NASA GSFC (Atmospheric Chemistry and Dynamics Laboratory): zonal-mean wind at 60° N from 10 to 150 hPa, mean polar-cap temperature 60–90° N at 10 hPa, wave heat flux 45–75° N at 100 hPa, daily values of the MERRA-2 reanalysis (Gelaro et al., 2017) then of the GEOS FP system for recent months, with the climatology of each date (1978/79 to 2025/26) and the GEOS forecast to about ten days. NOAA GEFS v12 ensemble (Zhou et al., 2022), 00 UTC run, 31 members to 35 days, read straight from the GRIB2 files published on AWS (only the 10 and 500 hPa fields are downloaded, by byte ranges).
Major warmings. Criterion of Charlton and Polvani (2007), applied to the NASA daily wind from 1979 to today and checked against the NOAA compendium (Butler et al., 2017): 26 of the 27 MERRA-2 events of the compendium (1980–2023) are found within one day, February 2002 is missing (lowest wind still positive in these files), three marginal one-day cases are added.
Vortex shape. Moments of the 10 hPa height on an equal-area polar projection (Matthewman et al., 2009): the vortex is the region below the mean height north of 45° N, weighted by its depth; aspect ratio of the equivalent ellipse and latitude of the centroid, thresholds of Seviour et al. (2013). Waves 1 and 2: Fourier amplitudes of the height along 60° N.
Surface. Composites of the Observatory test "stratospheric warmings → European winter" (window fixed in advance, 1,000 random draws of dates).
- Charlton et al. (2007)
-
Charlton, A. J., & Polvani, L. M. (2007). A new look at stratospheric sudden warmings. Part I: Climatology and modeling benchmarks. Journal of Climate, 20(3), 449–469.
· doi:10.1175/JCLI3996.1
Licence : Published literature; cited - Butler et al. (2017)
-
Butler, A. H., Sjoberg, J. P., Seidel, D. J., & Rosenlof, K. H. (2017). A sudden stratospheric warming compendium. Earth System Science Data, 9(1), 63–76.
· doi:10.5194/essd-9-63-2017
Licence : Published literature; cited - Baldwin et al. (2001)
-
Baldwin, M. P., & Dunkerton, T. J. (2001). Stratospheric harbingers of anomalous weather regimes. Science, 294(5542), 581–584.
· doi:10.1126/science.1063315
Licence : Published literature; cited - Polvani et al. (2004)
-
Polvani, L. M., & Waugh, D. W. (2004). Upward wave activity flux as a precursor to extreme stratospheric events and subsequent anomalous surface weather regimes. Journal of Climate, 17(18), 3548–3554.
· doi:10.1175/1520-0442(2004)017<3548:UWAFAA>2.0.CO;2
Licence : Published literature; cited - Matthewman et al. (2009)
-
Matthewman, N. J., Esler, J. G., Charlton-Perez, A. J., & Polvani, L. M. (2009). A new look at stratospheric sudden warmings. Part III: Polar vortex evolution and vertical structure. Journal of Climate, 22(6), 1566–1585.
· doi:10.1175/2008JCLI2365.1
Licence : Published literature; cited - Seviour et al. (2013)
-
Seviour, W. J. M., Mitchell, D. M., & Gray, L. J. (2013). A practical method to identify displaced and split stratospheric polar vortex events. Geophysical Research Letters, 40(19), 5268–5273.
· doi:10.1002/grl.50927
Licence : Published literature; cited - Kidston et al. (2015)
-
Kidston, J., Scaife, A. A., Hardiman, S. C., Mitchell, D. M., Butchart, N., Baldwin, M. P., & Gray, L. J. (2015). Stratospheric influence on tropospheric jet streams, storm tracks and surface weather. Nature Geoscience, 8(6), 433–440.
· doi:10.1038/ngeo2424
Licence : Published literature; cited - Domeisen et al. (2020)
-
Domeisen, D. I. V., & Butler, A. H. (2020). Stratospheric drivers of extreme events at the Earth’s surface. Communications Earth & Environment, 1, 59.
· doi:10.1038/s43247-020-00060-z
Licence : Published literature; cited - Gelaro et al. (2017)
-
Gelaro, R., McCarty, W., Suárez, M. J., Todling, R., Molod, A., et al. (2017). The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2). Journal of Climate, 30(14), 5419–5454.
· doi:10.1175/JCLI-D-16-0758.1
Licence : Published literature; cited - Zhou et al. (2022)
-
Zhou, X., Zhu, Y., Hou, D., Fu, B., Li, W., et al. (2022). The development of the NCEP Global Ensemble Forecast System version 12. Weather and Forecasting, 37(6), 1069–1084.
· doi:10.1175/WAF-D-21-0112.1
Licence : Published literature; cited - Northern stratosphere: polar vortex, polar-cap temperature and wave heat flux, daily (NASA GSFC, MERRA-2 and GEOS FP)
-
NASA GSFC Atmospheric Chemistry and Dynamics Laboratory, Annual Meteorological Statistics (Northern Hemisphere), from MERRA-2 (Gelaro, R., et al., 2017, Journal of Climate, 30, 5419–5454) and GEOS FP.
· doi:10.1175/JCLI-D-16-0758.1 · source page ↗
Licence : NASA data, no restriction on use (NASA Earth science data policy); cite MERRA-2 (Gelaro et al., 2017). The GEOS forecasts are experimental and given for research · retrieved on Oct 30, 2026 · SHA-256 6040839c0477… - GEFS ensemble forecast of the stratospheric polar vortex, 31 members to 35 days (NOAA NCEP)
-
NOAA NCEP Global Ensemble Forecast System (GEFS) version 12; Zhou, X., et al. (2022). The development of the NCEP Global Ensemble Forecast System version 12. Weather and Forecasting, 37, 1069–1084.
· doi:10.1175/WAF-D-21-0112.1 · source page ↗
Licence : U.S. Government work, public domain (NOAA Open Data Dissemination) · retrieved on Oct 30, 2026 · SHA-256 c4f4c690b073…