ern's: Lookback: May Lookback - Southeast Drought; Northwest Deluge, Jun 06

Monday, June 13, 2011

Lookback: May Lookback - Southeast Drought; Northwest Deluge, Jun 06 - 17:45

The first few days of May were dominated by a large blocking anticyclone in Arctic latitudes with strong easterly winds affecting the UK. From the 4th-10th a deep depression lay to the west of Ireland with southerly winds across the country, and from the 11th onwards lowest pressure was found to the west and north of Scotland with relentless southwesterly winds delivering copious amounts of rain to the western highlands, Cumbria, and parts of Northern Ireland.

Mean maximum temperature for May ranged from 19.4°C at St James's Park and Heathrow (both London) to 10.8°C at Fair Isle (between Orkney and Shetland), while mean minimum temperature varied between 10.8°C at Olympic Park South (London) and 4.0°C at Braemar (Aberdeenshire). Mean maximum temperature ranged from close to the long-term average in western Scotland to 2.5°C above in East Anglia. Mean minimum temperature was 1.0 to 2.0 °C above the long-term normal in all regions. The Central England Temperature (CET) of 12.3°C was 1.0 °C above the long-term mean, the highest for May for just three years. In parts of Southeast England, East Anglia and the Midlands May had a lower mean temperature than May - a rare event, but not without precedent.

The highest maximum at a standard site (i.e excluding rooftop and mountain sites) in the UK was 25.4°C at Weybourne (Norfolk) on the 7th, while the lowest minimum was minus 6.3°C at Altnaharra (Sutherland) early on the 4th. The lowest daytime maximum was 8.2°C at Dalwhinnie (Inverness-shire) on the 24th, and the warmest night was that of the 7th/8th with a minimum of 16.3°C at Weybourne (Norfolk).

Rainfall averaged over England and Wales during May was 48.9mm which is 80 per cent of the average for the standard reference period 1971-2000, higher than May 2010 but not as high as May 2009; in the last 100 years 31 Mays were drier while 69 were wetter. The equivalent figures for Scotland were 113.9mm and 187 per cent of the normal amount, and for Northern Ireland 66.4mm and 118 per cent. Monthly totals at routinely-available sites ranged from 468mm at Cluanie Inn (Wester Ross) to just 4mm at Manston (Kent). Substantial parts of East Anglia together with east Kent received less than 10mm rain during the month.

Sunshine averaged over England and Wales during May was 216.2 hours which is 107 per cent of the 1971-2000 mean, the lowest since 2008; in the last 100 years 45 Mays were sunnier while 55 were duller. The equivalent figures for Scotland were 195.7 hours and 112 per cent, and for Northern Ireland 199.7 hours and 98 per cent. Largest total in the UK was 273 hours at Manston (Kent) and the smallest was 117 hours at Kinlochewe (Wester Ross).

The gale in Scotland, Northern Ireland and northern England on the 23rd was probably the worst in May since 1962 (16 May), with gusts at low-level sites of 70 knots at Inverbervie (Kincardineshire) and 67 knots at Drumalbin (Lanarkshire).

The Central England Temperature for the spring quarter (March, April, May), was 10.4°C, the highest in the entire 352-year long record, beating by 0.2°C the previous record in 1893. England and Wales rainfall for the three-month period of 88mm was the lowest since 1990.