By Brian Gaze
The first look ahead to the autumn was issued in July and it strongly favoured above average temperatures with indications of it being drier than the norm in the south. How have things changed since then?
The Central England Temperature (CET) has consistently been above average so far this year.
July and August both brought periods of extreme heat and 40C was recorded for the first time in the UK.
Autumn 2020 was 0.5C warmer than average with a UK mean temperature of 9.9C.
The UK mean temperature for Autumn 2021 was 10.9C which is 1.4C above the 1981 - 2010 average.
The monthly temperature anomalies were:
September: 2.1COctober: 1.4CNovember: 0.8C
The UK rainfall total relative to the 1981 - 2010 average was 82%. The monthly statistics were:
September: 82%October: 128%November: 63%
Sunshine totals were 94% of the 1981-2010 average. The monthly statistics were:
September: 96%October: 87%November: 101%
In recent years there has been a tendency for months to be above rather than below CET and that trend has continued through 2022 so far. That is a significant consideration when looking ahead to the Autumn.
A sprinkling of autumn snow in Berkhamsted
The table below summarises output from seasonal forecast models for September, October and November 2022. It represents the data available at time of publication and subsequent updates may favour a different outcome.
Below average in the south east
Mixed across the UK
C3S multi system incorporates date from a range of sources including: ECMWF, UK Met Office, Meteo France, CMCC, DWD, JMA and NCEP.
There is a strong signal for temperatures to be above the average. The precipitation outlook is less clearly defined, but there are indications of it being drier than average in the south.
The relationship between autumn and winter has been discussed before. There are suggestions of a correlation between warm autumns and mild winters.
In addition to the seasonal models a number of other points are considered:
1) There is an 86% chance of La Nina continuing through this autumn. La Nina tends to support drier conditions during the meteorological autumn in Spain and parts of France. There is also a correlation with an increased incidence of cold weather in the UK during the late autumn and early winter.
2) A more active than normal hurricane season was forecast by the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center and other forecasters. However, the season to date has been notably quiet and if that were to continue the chance of cooler and changeable periods of weather early in the autumn may be increased.
3) High levels of global warmth.
4) Warmer than average seasons have been common in the UK during recent years. All months so far in 2022 have been warmer than the average. July and August brought exceptional spells of hot weather.
The above pointers are inconclusive. Recent climatology supports the idea of warmer than average conditions through the first half of the autumn, but the unexpectedly quiet hurricane season adds uncertainty. La Nina could increase the chance of cold spells in late November.
At this stage aggregate temperatures for the meteorological autumn (September, October and November) are considered more likely to be above average than below.
However, the confidence in this has lowered since the first update was published in July. In addition, the chance of colder than average periods may increase towards the end of the season.
On balance drier than average conditions are favoured, especially in the south.
The autumn forecast will be released at the end of August.
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Models include UK Met Office UKV and MOGREPS-G, ECMWF, NCEP GFS, Meteo France Arpege and Arome.