Yearly Weather Summary for Harpenden

Data supplied by ECN Rothamsted  (ECN AWS T06 02; Harpenden Meteorological Station)

Change of rain gauge and the effect on rainfall capture and data presented in Monthly Weather Summaries.

Rainfall up until 2004 was measured manually using a cylindrical rain gauge of five inch diameter (5") within a turf-wall enclosure to reduce wind turbulence. In 2004 the Met Station at Rothamsted was automated and the 5" rain gauge replaced with an aerodynamically shaped tipping bucket rain gauge of ten inch diameter (type ARG100) within the enclosure. The manufacturers of the ARG100 state that "the ARG100 raingauge typically captures over 5% more rainfall than most traditionally-shaped cylindrical gauges due to its unique aerodynamic shape and reduced evaporation-loss properties". This has been found to be the case at Rothamsted. When we have compared the ARG100 with the 5" we get a difference of approximately ten percent over an eight year period (2004 to 2011).

We have therefore decided not to correct rainfall data but to advise that this difference exists. This does however mean that the 30 year average rainfall data are to be considered for use as guidance only.

Previous summaries 2001 to 2024

Harpenden Highs and Lows

The table below shows for selected variables the long-term mean value*; the highest and lowest mean value recorded for each month and year since records began; and the year that it was recorded. Those values achieved this year are highlighted in Red.

**Mean air temperature is calculated daily as the maximum air temperature (Max) plus the minimum air temperature (Min) divided by two i.e. (Max+Min)/2