April rainfall - national/regional variation

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April rainfall - national/regional variation

Postby Martin Rowley » 2014 May 01, 12:42

... Not particularly unusual of course, especially in spring, but the EWP figure for April 2014 (and associated %age of LTA) is not going to tell the story of rainfall down here in the south of England. As Stephen Burt (Stratfield Mortimer, Berkshire) reported a few days back, he was running around 150% of average then ... and no doubt there's been more since.

Here in east Dorset, the total for our station (West Moors) = 115 mm (210% eLTA 1981-2010) & down the road, Hurn (provisional, based on 06-06 SYNOPs) = 115 mm (213% LTA 1981-2010).

The 'variation' I refer to in the subject is with respect to the England & Wales Precipitation total: up to rain-day 29th April, the Met Office have 53 mm, representing *under* 100% (they give 86%) and it's unlikely that any rainfall on the last day of April across the EWP domain would change those figures significantly.

In the published (Met O web site) record for Hurn [1957+], that total (115mm) placed April 2014 fourth-wettest such-named month, beaten by 2012, 2000 & 1961. 2000 was the wettest with 150 mm.

The first six-month/2014 total for Hurn = 581 mm (157% of 1981-2010 LTA) - by some margin, *already* [four months gone] the wettest such period in that record - helped along by the exceptionally wet January & February; the previous full six-month record was 1971 with 513 mm.

Has anyone else across the south of England (or elsewhere within the EWP domain) significant departure from what will be declared as the figure 'for the record'?

Martin.
Martin Rowley
West Moors, East Dorset [ altitude: 17 m/56' ]
NGR SU 082 023: postcode BH22 0GB
50deg49min15secN, 01deg53min03secW
Martin Rowley
 
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Re: April rainfall - national/regional variation

Postby Len Wood » 2014 May 01, 19:42

Martin.
My April total was 92.3 mm.
That is 138% of 1981-2010 average (66.9 mm).

However that is within the normal variability you would expect for April in these parts.
The standard deviation is 34 mm.
If the total had gone above 100mm it could have been described as significantly wet in the statistical sense.
Len

Wembury, SW Devon coast
N50.33 W4.13
Altitude 83 m asl
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Re: April rainfall - national/regional variation

Postby Martin Rowley » 2014 May 02, 09:42

Martin Rowley wrote:{snipped}

The 'variation' I refer to in the subject is with respect to the England & Wales Precipitation total: up to rain-day 29th April, the Met Office have 53 mm, representing *under* 100% (they give 86%) and it's unlikely that any rainfall on the last day of April across the EWP domain would change those figures significantly.

In the published (Met O web site) record for Hurn [1957+], that total (115mm) placed April 2014 fourth-wettest such-named month, beaten by 2012, 2000 & 1961. 2000 was the wettest with 150 mm.


... the 'final' (though still provisional) EWP total is declared as 58 mm, 98% of the 1961-1990 LTA (and 89% of the 1981-2010 data-set)

Following on from Len's comments on standard deviations etc., the Hurn April total is within 3 mm of two sd above the 1981-2010 LTA.

Martin.
Martin Rowley
West Moors, East Dorset [ altitude: 17 m/56' ]
NGR SU 082 023: postcode BH22 0GB
50deg49min15secN, 01deg53min03secW
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Posts: 154
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Re: April rainfall - national/regional variation

Postby Stephen Burt » 2014 May 03, 19:15

My final total for April was 94.0 mm, which is 183% of 1981-2010 normal, and 1.34 SD above the mean for that period.

Not exceptionally wet, therefore (2000 saw 157 mm and 2012 125 mm at this site, and there are numerous others > 94 mm on a local record back to 1862), but up to 19th inclusive only 10.8 mm had fallen, with 12 consecutive dry days ending 19th.

Total for Jan to April stands at 411 mm, 189% of the 1981-2010 normal. Put another way, if no rain whatsoever falls until the end of August, only then will we drop below normal for the year to date.

Stephen
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
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