September - second warmest in spite of below average sunshine

Written by Eric Gilbert on .

Beautiful September sunriseBeautiful September sunriseWilliam Cobbett the radical journalist and MP wrote in 1823  “The fog was so thick and white, that I should have taken it for water, if little hills and trees had not risen up through it here and there”.

We had three mornings in September that dawned with fog, the visibility down to 200 metres on September 15.  The picture was taken across the Og valley on September 11 when fog filled the valley rather than covering the whole countryside.

It was the second warmest September that I have recorded since my weather station began in 1984.  The mean was 2.1C above the long-term average with the nights particularly mild due to the frequent cloud cover and the unusual number of days with warm air from a southerly direction.

The record warm September was in 2006 when the mean was 3.1C above the 32-year average.  However the September of 1986 was very cool or even cold when the mean was 3C below the long-term average.

Strong sunshine totalled 87.4 hours.  I have no long-term average for this instrument as it was only installed in 2013, however, the September total this year is far lower than that recorded in September last year when we enjoyed 137 hours.

It is not surprising that solar energy was much lower than the average with just 88 per cent of the long-term average.

The warmest period occurred in the middle of the month with a peak of 25.8C on September 15, which is 7C above the mean.  Temperatures dropped off in the last week with maxima just below or close to the mean.

No air frost was recorded but it was very chilly in the early hours of several days with the lowest occurring on September 11 with a minimum of 4.9C.  It is interesting to look back over the records and see that no air frost has occurred in September since 2004.  However, in the 1980s an air frost was a not uncommon occurrence and in 1986 the thermometer dropped below zero on five nights.

Rainfall totalled 56.8mm, which is just 5mm below the 32-year average.  There were eleven totally dry days with the bulk of the precipitation falling on September 3 and 24 with 12.6mm and 10.2mm respectively.

Thunder was heard on September 13 starting at 12.40 for over half an hour and again later on that afternoon at 1525 for a similar period of time.