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October outlook

Indian Summer?


06/10/2018

September overview and early October

The provisional UK mean temperature for September was 12.4C which is 0.2C below the 1981-2010 average and the Central England Temperature (CET) was 13.7C which is 0.1C above the average. Rainfall was 108% of average taken across the UK as a whole, but there were significant regional variations with areas further south and east tending to be drier. So on balance the month was close to the climatological norm and despite the hot summer the anomalous warmth didn't continue into the early autumn.

October has started on a mixed note. Temperatures during the first few days have been above the average in the south but it has been colder and wetter in the north. What does the rest of the month have in store for the UK?

Autumnal scene

Indian Summer likely mid month?

During the second week of the month the UK is expected to become sandwiched between high pressure to the east and low pressure areas to the west. The pattern could become quite stable and difficult to break down. Since February there seems to have been an above average tendency for high pressure blocks to influence the UK's weather.

Last winter the Beast From The East weather pattern resulted from high pressure forming to the north of the UK and cold easterly winds blowing across Europe on its southern flank. In the summer high pressure blocks frequently prevented the cooler and more changeable Atlantic flow from reaching the UK, instead giving us hot and continental style periods of weather.

There is some uncertainty about where the boundary between the continental and Atlantic air masses will be during the middle part of October. However, it looks as if the Atlantic disturbances for most of the time are only likely to the west and north west. Further south and east a very warm south or southwest air stream is expected to persist for much of the period. Temperatures in southern and eastern counties could push up towards 24C (75F) during the second week of October as Indian Summer conditions develop.

GFS temperature chart for Thursday 11th October

More changeable later in the month?

During the last third of October there are some indications of more changeable weather spreading southeastwards. A number of computer model runs are showing Atlantic low pressure areas having more influence as an upper level trough develops near the UK. 



Despite that there could continue to be a lot of dry periods, especially in the south and east of the UK. The chart below shows the forecast pressure patterns on Monday 22nd October from each run in the GEFS ensemble computer model. The key things to note are:

1) Most runs suggest high pressure is more likely to be influencing the weather in the south and east.

2) The majority of runs show a good chance of disturbances from the Atlantic bringing wet and windy spells to the north west of the UK.

3) Most runs suggest temperatures will be close to or above the seasonal average during the days, however some chilly nights are possible further south and east where high pressure has more influence.

GEFS 06z postage stamp plot

Summary

During the middle of October it is expected to become warm and a period of Indian Summer weather is probable. In the north west it stays more mixed as Atlantic disturbances continue to influence things. During the second half of the month the more changeable conditions in the north west may push further south and east. Despite that it could stay drier than average in the south and east as high pressure blocks centred to the south and east remain influential. That would suggest the possibility of warmish days but chilly nights bringing fog and and a risk of frost.

TWO monthly forecast

From Brian Gaze, TWO founder
Since establishing TheWeatherOutlook over 15 years ago the site has grown enormously and running costs have risen. I intend to continue expanding TWO and keeping it free if possible. If you find it useful and would like to contribute to its development please consider making a donation.

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