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Summary for November and Autumn 2015

November 2015
With successive weather fronts crossing the country for most of the month it is not surprising that the mean temperature was 2.5C above the long-term average. It has been the 2nd warmest November since my records began in 1984.

Analysing the records since 1984 there is a slight but definite upward trend in the mean temperature for November over the past 20 years.

The warmest day was on the 6th with a maximum of 15.9C, which was 6C above the average. There were just three days when we had an air frost with a minimum of -2.9C on the 23rd. It was the second latest date in the autumn for the occurrence of an air frost.

The rainfall was 107.4mm that is 16mm above the long-term average with the wettest day producing 13.1mm on the 5th. There were only five totally dry days.

Cloud cover was continuous for many days, which meant that solar energy was well below average, just 80% of the total last year and strong sunshine amounted to 16.4 hours compared to 41.4 hours in 2014.

A major feature of the month was the number of days when we experienced very strong winds with gusts to 44mph on the 17th and nine days with gusts well above 30mph.

Autumn 2015
It has been a warm autumn with the mean temperature 0.2C above the long-term average. The mean temperature for the three-month period indicates an almost continuous upward trend over the past 20 years, increasing by around 0.3C.

It has been the driest autumn since 2011 with a total of 225mm, which is 16mm below the long-term average. The records show that 2006 was the wettest autumn with 401mm and 1985 the driest with just 116mm.

Only five dry days this month

The mild weather continues with yet more rain. The precipitation yesterday amounted to 3.4mm bringing the total for November to 83.1mm, just a little short of the long-term average of 91.1mm. The maximum temperature yesterday was 9.9C., average for this month, with the thermometer dropping little overnight to a minimum of 7.3C.

Average temperatures

With winds returning to a southerly direction temperatures have recovered. After a maximum of 5C during daylight hours, the thermometer continued to rise during the night with a peak of 9.6C although dropping back before dawn. The rainfall overnight amounted to 7.1mm.

First Air Frost of Autumn



Before we had central heating and well insulated homes, windowpanes had wonderful and intricate ice patterns when we pulled back the curtains in the morning following a hard air frost. I remember them well and the images here are examples that I took on 4th January 2009 when we had experienced nine consecutive nights with an air frost including when the thermometer plummeted to -13.3C on the 9th January.

With the subject of climate change continuingly being discussed and a major conference being held this month it is interesting to look at one aspect that affects us as autumn advances into winter.

Air frosts can mean attractive landscapes and frozen car windscreens when they occur. The severity of them tends to deepen as the winter moves into January and February.

Extracting and analysing data since my records began in 1984 reveals a changing pattern. I will take the period from 1985 for this article and use the data when the air temperature drops to or below -0.1C.

There is a distinct trend over the period for the occurrence of air frosts to occur later and later into autumn. Using 1st September as a datum and averaging the days since that date when an air frost occurs, I find the following trend. The first and last periods are for five years whilst the central periods cover ten years.

Year(Starting in) 1985 30
1990 33
2000 57
2015 66
Days since 1st September

We all realise that the mild weather experienced in autumn tends to last longer and delay the more severe weather of winter. Looking at the overall trend, these figures show the quite dramatic shift in the advent of an air frost each year, whilst recognizing that there are considerable variations from year to year.

September has been frost-free since 2004 whilst it occurred three times in 2003 with five in 1986.

During October an air frost always occurred up to 1999 when there were five days with the coldest recorded at -1.7C. The last three consecutive years have been without an air frost in October.

November is quite a different month in that the overall trend is flat for the number of air frosts. However, there are wide variations. We experienced an air frost on 15 days in 2005 contrasting with 4, 9, 8 and 4 over the last four years. This year the first air frost occurred on 21st November.

December provides quite a contrast in that the trend for the occurrence of an air frost has increased over the years from around 8 a month to 12 a month. There were 25 days with an air frost in 2005 and only 2 in 1988.

Details of the first air frost to occur each autumn since 2000 are in 2013 (11th November), 2000/04/05 (13th November), 2011 (23rd November) and this year the first air frost was on the 22nd November (-2.6C), which almost equaled the record in 2011.

The coldest night occurred on 20th December 1999 with a minimum temperature of -14.1C with the slightly lower figure of -13.8C on 11th February 2012.

The data above provides evidence that the climate in Marlborough has changed over the past thirty years or so but is this short-term change or evidence of more permanent climate change?