Blue Line: Daily rainfall (09:00 to 09:00) and Accumulated daily rainfall ; * Red Line: accumulated daily rainfall, 30 year mean (1981 to 2010 previously 1971-2000); Grey Line : +/- one standard deviation representing the variability of the data used to calculate the thirty year mean.
Measuring and recording precipitation that falls as snow
At the times at which precipitation falls as snow an automated rain gauge is prone to getting blocked. Here at Rothamsted, if such an event occurs during a work day, any snow remaining in our standard 5" cylindrical MK2 Met Office manual rain gauge funnel (MK2) at 09:00 is melted and precipitation measured. If snow has exceeded the height of the MK2 then using a spare 5" funnel a core of snow is taken, melted and measured. If any precipitation falls as snow after 09:00 on a Friday and over the weekend then it is not measured until 09:00 on the following Monday. All snow and ice present in any of the automated rain gauge funnels is removed.
When correcting data files for automated rain gauges, including the ECN automated rain gauge, with daily values of precipitation due to snow. We use the measurement from the MK2 taking into account that which has melted and been recorded previously. The corrected value is entered against the 09:00 timestamp for the day on which the measurement of precipitation that fell as snow was made. e.g. snow that fell during the period between 09:00 on a Friday to 09:00 on a Monday and is measured at 09:00 on that Monday. This corrected value is recorded against 09:00 for that Monday.
* The thirty year mean (1981 to 2010) for rainfall should be used only for guidance. This is due to the fact that rainfall measured during this period was two different rain gauges (see main Rothamsted Weather page).