Autumn 2024 weather forecast

Autumn typically brings a wide range of weather conditions and in that sense this year is unlikely to be different. The season is likely to coincide with a switch from El Niño to La Niña conditions in the eastern Pacific. That could increase the chance of early cold spells.

In addition, there have been suggestions from some computer model runs of a weaker than average Stratospheric Polar Vortex (SPV). Were this to be correct, it would also potentially increase the chance of cold spells occuring in November.

Despite that, computer models are forecasting above average temperatures over the season as a whole as the most likely outcome.

Forecast considerations

The forecast was produced by looking at a number of factors, including:

• Seasonal forecast models
• Persistence patterns during recent seasons and historical analogues
• El Niño-Southern Oscillation  (ENSO) conditions
• Stratospheric Polar Vortex (SPV) forecasts
• Atlantic sea surface temperatures (SSTs)
• Solar activity
• Summer weather patterns and temperature trends
• The Weather Analogue Index (WAI) which was tracked through the summer months

Long range forecast confidence

Seasonal models suggest a milder than average season. On balance, recent climatology does too, although the summer was marginally cooler than the 1991-20 average.

Background signals are mixed, but the transitioning ENSO phase correlates with a weakened Atlantic flow late in the season, as would a weaker SPV.

The top 45 day WAI matches are with years which produced close to average or rather cool autumns.

Therefore, although a slightly milder and slightly wetter than average autumn is forecast, other outcomes are very possible. Long range forecasts are only intended to give an idea of very broad brush trends, such as whether a season may be wetter or drier, or colder or milder relative to the long term averages.

TWO autumn 2024 forecast

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