Marlborough's weather chalks up another 2016 headline: December was the driest month of the year

Written by Eric Gilbert on .

Fog forming at dusk in the River Og ValleyFog forming at dusk in the River Og ValleyIn 1862, George Elliot, the novelist wrote: “The constantly heavy-clouded and often wet weather tends to increase the depression. I am inwardly irritable and unvisited by good thoughts”.  

There were so many days in December when this description applied to the Marlborough area: very thick, low cloud and days with fog occurred all too frequently. There were sixteen days when no Ultra Violet light was measurable and on four days there was thick fog - that's with visibility down to 100 metres.

Despite the many days that were damp with fog, December was mild with little rain.  Climatologically speaking this is a relatively rare combination because typically mild Decembers are wet and cold Decembers are dry.

Although there were thirteen days with measurable precipitation, the rainfall for the month amounted to just 22.6mm. The wettest day was December 10 when 8.5mm fell.  And that was over a third of the total for the month.

This makes December 2016 the third driest December I have recorded since the weather station was started in 1984 and remarkably for a winter month, the driest month for the whole of 2016.

The 32-year average for December rain is 91.5mm - giving a 2016 deficit against that average of 68.9mm. The two previous very dry Decembers were in 1991 and 1988 with 21.8mm and 17.6mm, respectively. The record for Marlborough's December rainfall was in 2013 when 157mm were logged.

It is not surprising that the Rivers Kennet and Og are running so low as although November rainfall was above average, the October total was, like December, very low. The rainfall for the whole of 2016 was 767 mm, which is 91 per cent of the 32-year average or 72mm below.

Although there were eleven days when an air frost occurred, it was a mild month with the mean 0.7C above the long-term average. There were a couple of colder spells at the beginning and end of the month, but there were twenty-one days when the maximum exceed the mean for December.  

The warmest day occurred on December 9 when the thermometer rose to 13.7C, which was 6C above the mean. The coldest night was measured on the 1st of the month when a minimum of -7.1C was recorded followed by -6.3C on December 2.

The peak barometric pressure was on December 27 with a reading of 1044.9mb and any wall barometer at home, accurately set, would have shown the arm far around to the right at the ‘Very dry’ setting. In fact it was the highest December barometric pressure I have recorded since 1991.

Many days were very calm as the intense high pressure dominated for much of the month. This resulted in many days with stagnant air and some days with hardly a movement of the air for extended periods.  

For example, on December 27 the anemometer measured a peak of just 5mph for the whole day with two very similar days when a maximum was 6mph, which cannot be classed as a gust of wind, rather just a brief movement of air. In contrast to this calm scene was the very breezy day that occurred the day before Christmas Eve when a maximum gust of 41mph was recorded.

To look on the bright side there fifteen days with strong sunshine - with the sunniest occurring on December 29 with 5.77 hours of sunshine.

The very dry Decembers of 1988 and 1991, as mentioned above, were followed by very dry Januaries each with between a half and a third of the mean monthly rainfall. However, January 1989 was mild and January 1992 cold, so there is no consistent trend to note there.

What will January 2017 bring?

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