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graphs CLIMATE-UK.COM'S REVIEW OF THE BRITISH METEOROLOGICAL SCENE
MONTHLY SUMMARY
No. 641 For MAY 2009
A RATHER CHANGEABLE MONTH WITH A DRY SUNNY FINISH
Text Box: May was a changeable month with no dominant circulation type; an unsettled westerly flow lasted from the 2nd-9th, followed by shortlived easterly, cyclonic/southerly, anticyclonic, westerly and anticyclonic/easterly spells. Mean monthly sea-level pressure was within 2mbar of the long-term normal throughout the British Isles, and the anomalous flow over the UK was weakly southerly.

The month opened with a southerly airstream between a deep depression northwest of Ireland and high pressure over the Baltic, but a westerly type held sway from the 2nd until the 9th. A strong rise in pressure on the 10th led to the establishment of an anticyclone to the north of Scotland and a brisk easterly flow covered the UK from the 11th-14th. The 1st was fair and warm in southern, central and eastern districts with 21.5C logged at Weybourne (Norfolk), but the next week was changeable and rather windy with rain-belts crossing the country at frequent intervals although there was sunshine between. Amounts of rain were small in the east and south, but 47mm fell at Tyndrum (Perthshire) on the 6th alone with 133mm between the 5th and 9th inclusive. A gust of 63kn was recorded at West Guerinish (Western Isles) on the 7th. The weather became quieter on the 9th and 10th with sunny spells in Scotland and also in southern England. The next two days were mostly fine, although a cold east to northeasterly flow affected England and Wales and the wind approached gale force in the English Channel; in Scotland and Northern Ireland days were warm but nights were frosty, with -4.7C at Kinbrace (Sutherland) early on 11th and -4.6C at Aboyne (Aberdeenshire) on the 12th. Southern districts became dull with occasional rain on the 13th and 14th, and late on the 14th heavy rain spread northwards across the country with 34mm at Scampton (Lincs).

On the 15th a depression transferred from southeast to northwest across the country, and from then until the 21st low pressure was anchored close to Ireland with a showery southerly airflow covering much of the UK. Hail and thunder occurred locally on several days. It was cold in eastern Scotland on the 15th with a maximum of just 7.6C at Text Box: Braemar (Aberdeenshire), otherwise daytime temperatures were generally near normal though it was often rather mild at night. 

A strong upper ridge developed over Britain between the 22nd and 25th but a thundery trough affected parts of England and Wales later on the 25th ahead of an eastward-moving cold front. Two days of brisk westerly winds were followed a renewed build of pressure, and an intensifying anticyclone moved northeastwards across England on the 28th to take up residence over southern Scandinavia for the remainder of the month. It was very warm from the 23rd-25th; the 24th was brilliantly sunny and 25.2C was reached at Northolt (London), but the 25th was somewhat cloudier with local showers though it was scarcely any less warm. Thunderstorms broke out towards evening in the Southeast, East Anglia and Lincolnshire. The 26th was cooler and windier with long sunny spells after the clearance of early rain from eastern England, but the 27th was cloudy with some rain in most places. It became very warm and mostly sunny during the remainder of the month - high humidity on the 28th was relieved by a freshening easterly flow thereafter. The temperature fell no lower than 14.6C at Hawarden (Flintshire) overnight 27th/28th, while afternoon highs of 22-25C occurred widely, and 26.5C was logged at Cassley (Sutherland) and Kinlochewe (Wester Ross) on the 29th, 26.4C at Cassley on the 30th, and 26.7C at Lee-on-Solent (Hants) on the 31st. The sun shone for 16.8h at Altnaharra (Sutherland) on the 29th and at Inverbervie (Kincardineshire) on both the 30th and 31st.

Mean temperature was 0.5-1.5degC above the 1971-2000 average in most parts of the country, and 1.5-2.0degC above locally in East Anglia and the Southeast, but it was not as warm as May 2008. Rainfall ranged from almost twice the normal in parts of the western highlands to less than 50% at several sites in eastern England. Total sunshine for the month was above normal everywhere with greatest excesses (around 50% above normal) in northern and eastern Scotland.
                                                                                                                                             
    TEMPERATURE   SUNSHINE   RAINFALL        
                                                                                                                                     
                                                                                                                                     
                                  Highest and lowest totals             Highest and lowest totals        
                                  on record for month    
Maximum fall in 24 hrs
   (beginning 09 h)
        on record for month    
Days with snow or sleet
 
Days with fog
(Vis <220 yards at 09 h)
 
                                                                                         
     
Difference from average
   
Difference from average
 
Highest maximum
   
Lowest minimum
   
No. of days with grass
  minimum below 0C
   
Days of no sunshine
 
Maximum duration
       
First year of record
         
Days of no rainfall
 (0.1 mm or less)
         
First year of record
         
Days with thunder
     
  PLACE  
Mean Maximum
   
Mean minimum
             
No. of air frosts
       
Total for month
                   
Total for month
                   
                               
% of average
                   
% of average
                 
                                                                     
                                   
Highest
   
Lowest
 
Year
             
Highest
   
Lowest
 
Year
       
             
Date
   
Date
         
Date
         
Year
         
Date
         
Year
           
                                                                     
    C     C     C     C           Hrs     Hrs       Hrs     Hrs       mm     mm       mm     mm          
                                                                                                                                             
  *Hampstead   17.6   +1.6   08.8   +1.2   24.1   31   03.9   04   02   00   02   12.1   30   182   100   1910   297   1989   112   1932   18   14.1   25   031   053   1910   124   1979   04   1989   00   00   00  
  *Thorney Island   16.8   +0.2   09.0   +1.5   24.5   31   03.3   04   01   00   00   16.0   30   224   104   1958   322   1989   151   1981   17   09.0   25   034   078   1941   103   1946   04   1989   00   00   00  
  *Wattisham   17.2   +1.6   07.8   +1.6   21.7   31   01.3   04   04   00   02   15.4   30   203   106   1968   331   1989   127   2006   15   10.2   14   037   084   1960   119   2007   05   1989   01   00   00  
  *Wittering   17.1   +1.9   07.9   +1.3   23.4   29   02.8   04   04   00   02   15.2   30   201   099   1955   299   1989   113   2007   18   07.0   25   022   047   1955   116   1983   09   1990   01   00   00  
                                                                     
  Lyneham   16.3   +0.9   07.6   +1.0   23.7   29   03.4   04   02   00   03   15.5   30   226   113   1945   288   1990   112   1981   18   09.4   18   027   047   1945   139   1967   05   1990   00   00   00  
  Ross-on-Wye   17.6   +1.9   08.1   +0.9   25.7   29   02.8   04   01   00   04   14.4   31   224   120   1915   285   1992   104   1932   17   07.9   16   038   063   1859   158   1967   05   1896   00   00   00  
  *St Athan   15.4   +0.4   08.9   +1.6   23.9   31   04.9   04   00   00   03   14.7   30   200   097   1954   318   1990   119   1981   14   08.6   14   044   070   1954   155   1983   05   1991   00   00   00  
  Culdrose   14.2   +0.7   08.7   +0.4   20.4   31   03.1   10   00   00   03   14.3   31   209   093   1961   275   2004   124   1981   19   10.8   14   040   067   1961   141   1993   06   1991   00   00   00  
                                                                     
  *Edgbaston   16.4   +0.9   08.2   +1.3   24.2   29   04.0   10   00   00   01   14.3   12   184   110   1887   263   1997   094   1954   15   21.4   14   053   094   1887   173   1932   05   1896   01   00   00  
  *Valley   14.4   +0.1   08.9   +1.1   22.5   30   05.6   12   00   00   04   15.5   30   205   091   1946   306   1977   161   1970   15   10.4   14   039   069   1941   127   1993   10   1970   00   00   00  
  *Woodford   16.0   +0.9   07.4   +1.0   24.0   29   02.6   04   05   00   05   15.2   31   166   094   1945   258   1989   111   1991   11   17.2   14   085   142   1942   144   1967   08   1991   01   00   00  
  *Watnall   16.6   +1.4   07.8   +1.2   24.6   29   03.8   17   03   00   02   15.3   30   180   089   1948   276   1989   085   1983   11   12.4   15   049   103   1942   135   1969   11   1991   00   00   00  
                                                                     
  *Leeming   16.6   +1.6   06.6   +0.3   23.6   29   00.6   12   04   00   02   15.5   31   204   115   1945   238   1980   103   1983   14   15.0   15   042   087   1947   106   1983   09   1959   00   00   00  
  *Boulmer   14.9   +2.4   07.0   +1.2   19.4   24   03.3   11   06   00   02   14.9   31   221   125   1945   231   1989   098   1983   15   08.6   15   028   054   1945   151   1924   07   1992   00   00   00  
  *Eskdalemuir   14.2   +0.6   05.1   +1.0   23.4   29   00.0   10   10   00   03   14.8   30   164   099   1911   268   1935   079   1969   08   25.6   05   157   165   1911   257   1986   04   1984   00   00   00  
  *Bishopton   14.9   -0.1   06.7   +0.7   24.2   31   01.5   11   02   00   04   15.1   31   178   095   1921   266   1975   098   1983   11   16.6   17   103   163   1921   156   1925   07   1991   00   00   00  
                                                                     
  *Leuchars   14.8   +1.4   06.0   +0.2   20.7   28   -00.3   12   12   01   01   15.8   30   222   118   1922   256   1942   095   1969   15   12.0   15   055   109   1922   152   1969   14   1959   00   00   00  
  *Dyce   14.6   +1.8   05.5   +0.4   22.0   28   -00.2   11   13   01   01   15.8   30   222   127   1941   256   2001   086   1983   11   22.2   15   088   147   1942   152   1969   14   2008   00   00   00  
  *Stornoway   13.5   +1.3   06.9   +0.9   20.8   30   02.6   11   04   00   01   15.2   12   200   106   1880   294   1994   093   1944   10   14.0   07   100   161   1943   145   1986   13   2008   00   00   00  
  *Aldergrove   15   +0.3   07.7   +1.6   22.2   31   03.1   10   01   00   04   15.2   31   177   089   1927   295   1946   115   1933   09   07.4   19   055   106   1927   131   1993   07   1991   01   00   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative. Thorney Island's      
  sunshine figures are from a nearby site.