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July in SE Dorset - a 'wet' month?

PostPosted: 2015 Jul 25, 13:18
by Martin Rowley
... rainfall yesterday, the bulk of which fell in the 17 hours between 0300 and 2000 Z (24th)[i.e. spanning two rain-days] amounted to 26.4 mm. This seems to fit well with other reports in the immediate area.

With that fall, our July monthly rainfall (so far) = 82.8 mm, representing 218% of the estimated 1971-2000 LTA / 169% 1981-2010 LTA.

So, a 'wet month' will present itself to anyone looking at the records in years to come. The difference from previous wet Julys of course (since we moved here in 2007), such as 2007 and 2012, is that the bulk of this rainfall has come from just two 'events': the 50 mm fall [thunderstorm] in just under an hour overnight 3rd/4th, and that of yesterday, so ~90% of the rainfall this month came from just two synoptic events.

It's more instructive to looks at rain-days with >= 1mm of rain recorded ( a 'wet' day) for these years: in July 2007 the figure was 18 days, in 2012 it was 15 days and this July it is just 5 days.

Nothing unusual about all this of course, but as July is our driest month on average (with the lowest standard deviation on a 30-year base), it does emphasise the danger of simply looking at the 'final figure' for rainfall for the month (with %age on LTA) to assess the character of any month - particularly a summer month: In fact, I've only just given up watering the garden!