May is the last month of spring and whilst the overall trend is to warmer and longer days it can still throw up a few surprises (there were more Air Frosts (7) in May than in April for example), this May was basically cooler and sunnier than the normal, but the one significant aspect was: IT WAS VER DRY.
May has become my driest month on record with just 14.8mm (0.58 inch) of rain - this fact is now becoming quite significant as the year to date as been very dry. With just 173.4mm for the year and in turn Feb', then April and now May have all been my 'driest' months. In the last 2 years that figure of 173.4 mm as been passed on the 21st JANUARY!!!!
The terms 'Drought' and 'Dry spell' came into play as the lack of rain continued. This was in main due to the presence of high pressure for the vast majority of the month.
A 'partial drought' is a 'period of at at least 29 consecutive days whose mean daily ppt does not exceed 0.2mm'. Our partial drought was exactly the 29 days (7.4.10. - 5.5.10) when we saw just 3.2mm of rain.
A dry spell is 'a period of at least 15 consecutive days to none of which is credited 1.0mm (0.04 inch) - our dry spell lasted 17 days (11.5.10. - 27.5.10.) with just 1.2 mm of ppt.
The three month mean (Spring) detailed below show that this it has also been a cooler Spring than the norm'.
So May was dry, cool and sunnier than average, but then in many ways it was a quiet month with not too much happening.
The month started with a bank holiday weekend and was on the cool side, but it was dry, with a mix of sunny and part cloudy days. From the 2nd high pressure in the Atlantic started to take control, but with the air flow circulating up and around this high, it introduced a cool Northerly flow. The 2nd/3rd were sunny days, but cool by day and night.
By the 5th the high pressure was still west of Eire, but weak fronts spread east over the Uk and it became cloudy.
Rain of 3.6mm on the 6th (months wettest day) broke the partial drought. Weather fronts associated to low pressure with several centres spread south over the UK in the early hours.
From the 7th the area of high pressure was south of Iceland, with another high over the Baltics and an area of low pressure covering south Europe. Between these three areas a NE'ly air flow developed and we were still experiencing cool but relatively bright weather. The 10th saw artic air flowing south with a succession of weather of fronts and we now had the months coldest day, just 8.1°c (46.58°F) and also 2.8mm of rain.
And then the nights became even colder, we had Air Frosts on 9/11/12/13th with the months lowest temp' of -2.3°c (27.86°F) on the 12th. Ground frosts were typically -4.0°c with a low of -4.5°c on the 11th. As as been the case for so much of the year it was high anti-cyclonic pressure south of Greenland that was the dominant factor in our weather.
By now we were well into a period of dry days and it was only rain on the 19th that prevented us experiencing an Absolute drought (at least 15 consecutive days with no recordable rain).
From the 15th the temperatures started to pick up. We were still influenced by high pressure, although only weak ridges it was sufficient to maintain some sunny spells with the occassional cloudy day.
By the weekend of 22/23rd high pressure was established over France and brought a W-SW airstream with relatively warm and humid air. It was warm and sunny and the Friday (21st) reached 23.8°c with both the 22nd and 23rd peaking at 24.2°c (75.56°F). Maybe the downside was the high humidity.
The 24th remained warm, but then the temperature dropped quickly away and we back to those cool days. We went from that 24.2°c to the 26+27th both peaking at 11.7°c (53.06°F).
The 27th was also notable for providing us with an air frost with a minimum of 0.0°c. Not unheard of this late in the season, but still uncommon.
We also had the rarity of rain been recorded on five successive days (26-30th), but some of this fell overnight and hence wasn't that noticable. Low pressure was covering the Atlantic which had various rain bearing fronts and a strong Sw'ly flow that travelled east over the UK.
Obviously the last weekend of the month was a bank holiday and whilst the Saturday (29th) started poorly with rain all afternoon, Sunday was more a showery and sunny intervals day and the Monday (31st) saw a return to sunny conditions and was a reasonably warm day - a mixed bag then for a bank holiday.
At various sites in Cumbria and Lancashire this May is been reported has the coolest since 1996
The Mean Temperature for the month was 9.36°c+ - the Mean Max' was 14.28°c and the Mean Min' 4.45°c.
We had 7 Air Frosts in the month (62 for 2010) and Grass frosts totalled 9 (93 for 2010).
COMPARISONS:-
* May 10 rainfall was 30.7% of the average for 08-09
* May 10 was 1.2°c colder than May 2009 +
* May saw 22 dry days.
* March/April/May 2009 was TEMP' 8.21°c - RAIN 155.20 mm
* March/April/May 2008 was TEMP' - RAIN 217.00 mm
* 2010 TO DATE TEMP' 4.78°c - RAIN 173.4 mm
* 2009 Jan - May TEMP' 6.45°c - RAIN 410.7 mm
* 2008 Jan - May TEMP' - RAIN 536.5 mm
JANUARY 2010
FEBRUARY 2010
MARCH 2010
APRIL 2010
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+ Met office figures for May show that NW England/N. Wales had a mean temp' of 9.7°c, some -0.4°c colder than the reference period 1971-2000 (-0.2°c colder than reference period 1961-90)