Dartmoor Weather – Love It or Hate It! 

by Will Hand – 13th November 2015.

The Dartmoor Society Research Lecture 2015

Will Hand: ‘Dartmoor Weather – Love It or Hate It!’

Dartmoor Society members, friends and weather enthusiasts gathered at the Dolphin Hotel on Friday 13th November to hear meteorologist, Will Hand, talk about the data he has gathered from his weather station at Haytor over the past 13 years. Will began by telling us that he did not like Dartmoor weather, he loved Dartmoor weather, and this set the tone for an entertaining evening.

The manual instruments at the Haytor weather station record temperature, including ground temperature, rainfall and wind. The frequency of snow, humidity (foggy conditions) and thunderstorms are observed by Will, his family and his neighbours, who between them provide a comprehensive year-round record, even when Will is not at home!

As well as the manual instruments, an automated weather station (AWS) has been installed at the Haytor site since 2003, (the Davis Vantage Pro Automatic weather station), and this collects temperature, humidity rain and wind data. The information from the AWS is wirelessly transmitted to a computer at 10 minute intervals and this data is then used for statistical analysis on the website. There are also a weekly weather discussion and a longer term forecast.

The instruments at Haytor record the local weather picture, sheltered from the west, but exposed to the east. Rain falls in copious amounts, but not in the volume found on the high moor. The wettest month in the period 2003–2014 was November 2009 with 418mm of rain compared to the average November rainfall of 178mm. The wettest day was 22 March 2013 with 70.8mm recorded. The average March rainfall is 117mm for the entire month! The driest and warmest month over the period has consistently been September, which Will ventured to suggest was a good month to choose to holiday on Dartmoor!

It is generally recognised that in order to identify longer term trends, a record spanning at least 30 years is required. A number of local and national historical data sets are used by Will for this purpose. Weather data was recorded at Dartmoor Prison, Princetown from 1903 until 1990. This provides data at a high altitude. A lower altitude weather record is from Den Gardens, Teignmouth, which has been collecting data since 1900. Haytor sits roughly halfway between Princetown and Teignmouth, and the data sets are adjusted to produce estimated data for Haytor for the 30-year period 1971–2000. The data from the weather station at Haytor 2003–2014 is added to the estimated data from 1971–2000 to provide an almost continuous 40-year data set.

From this a slight warming trend can be identified. Spring is warmer, but December temperatures are getting colder (although we have just experienced a remarkably warm December 2015!). Spring and summer are becoming a bit wetter and the autumn and winter seasons are tending to be dryer. Snowfall, which is variable on Dartmoor, is always found in the colder months but less snow is falling and is not settling for long periods.

Many of us have been following the weather discussions on the Haytor Weather Station website, and our thanks go to Will for a fascinating evening where we learned a good deal about the process of recording weather and gained some insights into local weather patterns.

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