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graphs CLIMATE-UK.COM'S REVIEW OF THE BRITISH METEOROLOGICAL SCENE
MONTHLY SUMMARY
No. 677 For MAY 2012
RATHER COOL AND UNSETTLED DURING THE FIRST THREE WEEKS, THEN SUNNY AND WARM
Text Box: Mean sea-level pressure was almost uniform over the British Isles, indicating a sequence of synoptic types which largely cancelled each other out. A northeasterly type lasted until the 6th followed by short-lived cyclonic, anticyclonic, northwesterly and again cyclonic episodes. A strong ridge from a Scandinavian anticyclone dominated from the 22nd-27th, followed by a slack pressure pattern during the closing days of the month. The anomaly pattern was more clearcut, with a +7mbar centre south of Iceland and a northeasterly anomalous flow over the British Isles.

Pressure was high near northern Scotland during the opening days of the month, but only the highlands and islands enjoyed warm sunshine with 20C exceeded locally. By contrast much of England and Wales was cool and cloudy with rain at times; the rain was heavy in some central and southern parts overnight 2nd/3rd with 32mm in 12h at Charsfield (Suffolk) and radar returns suggest more than 60mm may have fallen in northeast Essex. It turned much colder in Scotland on the 4th, and the maximum at Fair Isle on the 5th was a mere 4.5C - the month's lowest. More notable, though, was a high of just 5.5C on the 6th at Wych Cross (Sussex). Sharp overnight frosts affected Scotland and northern England between the 5th and 9th; the lowest reading was -6.2C early on the 5th at Saughall (Ayrshire). Two depressions tracked northeastwards across the country on the 8th and the 10th, delivering widespread rain but also rather higher temperatures. On the 9th 36mm fell at Capel Curig and Porthmadog (both Gwynedd) and on the 10th there was 34mm at Shap (Cumbria). 

An intense anticyclone travelled eastwards along the 50th parallel on the 11th/12th and the pressure climbed to 1043.0 mbar at Valentia Observatory on the 12th - a new British Isles record for May. These were mainly dry days with sunny periods, though there were occasional showers in the north and east. A deep depression tracked northeast past the Faeroes on the 13th/14th bringing strong westerly winds gusting 50-60kn and heavy orographic rain to western Scotland, northwest England and parts of Wales. Some 119mm fell at Kinlochewe (Wester Ross) with 99mm at Loch Shin Text Box: (Sutherland) and 80mm at Cluanie Inn (Wester Ross) in the 36h ending at 09 GMT on the 14th. The 14th and 15th were cool showery days, the showers accompanied by hail and thunder in many places, but rising pressure on the 16th and 17th led to a reduction in the showery activity, although frontal rain affected northern and western districts. The 20th was the last of the cool and dull days with highs below 10C even locally in southern England, though it was generally dry.

A col lay over the UK from the 20th to the 22nd, but an anticyclonic/easterly type held sway from then till the 28th. The weather became mostly sunny from the 20th in Scotland, and from the 22nd over central and eastern England, with rapidly rising temperature and humidity. Highs above 26C were logged daily from the 22nd to the 29th, with maximum values of 28.7C at Kinlochewe (Wester Ross) on the 25th and 29.0C at Cromdale (Moray) on the 27th. It was abnormally warm at night, too, notably overnight 24th/25th when a minimum of 18.3C was logged at Cardiff/Bute Park. Highest daily sunshine duration was 16.6h on the 23rd at Auchincruive (Ayrshire). During the closing days of the month the weather became somewhat cooler and cloudier with isolated showers and thunderstorms.

The coolness of the first three weeks was offset by the warmth of the last ten days; mean monthly temperature anomalies ranged from 0.5-1.0 degC below in northern Scotland to 0.5-1.0 above in southeast England. Rainfall was rather above normal in many parts of eastern Scotland and northeast England, but was generally below normal elsewhere; monthly totals varied between 158mm at Kinlochewe and 12mm at Manston (Kent). Little rain fell in northern and western Scotland except on the 12th-13th. Sunshine aggregates ranged from 20-60 per cent above normal in northern and western Scotland to 20 per cent below in parts of East Anglia and the Southeast. Monthly totals varied between 273h at both Tiree (Argyll) and Fair Isle (between Orkney and Shetland), and 150h at Durham. In the London area there was less than 60h sunshine (<3h/day) during the first three weeks, but over 100h (>10h/day) during the last ten days.
                                                                                                                                             
    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   17.0   +0.6   08.8   +0.8   25.9   27   02.5   16   03   00   03   12.6   25   153   084   1910   297   1989   112   1932   15   08.4   09   032   056   1910   124   1979   04   1989   00   00   00  
  *Thorney Island   16.6   -0.4   09.0   +1.1   26.3   25   01.7   07   01   00   02   14.3   26   224   404   1958   322   1989   151   1981   17   13.4   09   042   094   1941   103   1946   04   1989   00   00   00  
  *Wattisham   16.2   +0.2   08.1   +1.5   25.8   28   00.3   16   02   00   05   15.2   25   155   081   1968   331   1989   127   2006   16   26.4   02   056   127   1960   119   2007   05   1989   01   00   00  
  *Wittering   16.1   +0.5   07.6   +0.6   25.4   28   00.9   06   03   00   06   14.5   26   169   083   1955   299   1989   113   2007   18   10.4   07   034   073   1955   116   1983   09   1990   01   00   00  
                                                                     
  *Lyneham   16.6   +0.8   07.8   +0.8   25.7   27   01.5   12   03   00   06   14.9   26   175   087   1945   288   1990   112   1981   18   12.4   07   055   093   1945   139   1967   05   1990   01   00   00  
  Ross-on-Wye   17.6   +1.5   08.1   +0.5   26.7   23   01.5   13   03   00   00   12.6   26   205   110   1915   285   1992   104   1932   20   10.4   30   050   082   1859   158   1967   05   1896   01   00   00  
  *St Athan   15.9   +0.5   08.9   +1.2   26.5   25   03.2   12   03   00   04   14.5   26   223   108   1954   318   1990   119   1981   19   20.0   02   060   096   1954   155   1983   05   1991   00   00   00  
  Culdrose   14.5   +0.6   08.7   +0.0   21.8   25   02.0   06   02   00   02   14.0   25   215   095   1961   275   2004   124   1981   19   09.6   26   030   051   1961   141   1993   06   1991   00   00   00  
                                                                     
  *Edgbaston   16.2   +0.3   08.1   +0.8   26.0   27   02.0   05   01   00   03   14.0   26   211   126   1887   263   1997   094   1954   16   12.0   30   051   090   1887   173   1932   05   1896   01   00   00  
  *Valley   14.9   +0.2   08.0   -0.2   26.1   25   02.2   05   01   00   04   15.2   26   221   098   1946   306   1977   161   1970   14   21.8   09   048   084   1941   127   1993   10   1970   00   00   00  
  *Woodford   16.3   +0.8   06.3   -0.5   26.0   24   -01.4   05   09   01   04   15.1   26   200   113   1945   258   1989   111   1991   19   17.2   09   051   084   1942   144   1967   08   1991   01   00   00  
  *Watnall   16.1   +0.5   07.6   +0.6   26.0   24   00.0   06   05   00   06   14.9   26   184   090   1948   276   1989   085   1983   18   18.0   09   037   080   1942   135   1969   11   1991   01   00   00  
                                                                     
  *Leeming   15.0   -0.4   06.0   -0.7   25.9   28   -03.0   06   08   02   05   15.3   26   177   099   1945   238   1980   103   1983   19   16.8   09   064   130   1947   106   1983   09   1959   01   00   00  
  *Boulmer   12.2   -0.7   06.2   0.0   20.2   24   00.6   06   03   00   04   15.3   26   180   102   1945   231   1989   098   1983   17   17.8   10   077   146   1945   151   1924   07   1992   00   00   00  
  *Eskdalemuir   14.5   +0.5   04.3   -0.2   26.8   23   -04.0   06   09   06   07   15.3   26   183   111   1911   268   1935   079   1969   15   17.8   10   082   086   1911   257   1986   04   1984   01   00   00  
  *Bishopton   15.8   +0.4   06.1   -0.3   27.3   24   -03.0   05   04   01   06   16.1   26   210   112   1921   266   1975   098   1983   18   18.0   13   057   090   1921   156   1925   07   1991   00   00   00  
                                                                     
  *Leuchars   12.3   -1.5   05.3   -0.9   19.9   27   -00.8   05   08   01   06   15.7   26   203   108   1922   256   1942   095   1969   14   13.0   30   066   129   1922   152   1969   14   1959   00   00   00  
  *Dyce   12.6   -0.6   05.2   -0.3   22.6   27   -01.8   07   05   02   05   15.5   26   190   109   1941   256   2001   086   1983   15   07.4   08   037   061   1942   152   1969   14   2008   00   00   00  
  *Stornoway   12.2   -0.4   05.5   -0.9   23.2   26   -00.9   07   05   02   00   16.3   30   245   130   1880   294   1994   093   1944   15   14.2   13   043   070   1943   154   2011   13   2008   00   00   00  
  *Aldergrove   15.4   +0.3   06.7   +0.2   25.0   25   00.7   05   07   00   01   15.5   26   197   100   1927   295   1946   115   1933   16   08.8   10   037   071   1927   131   1993   07   1991   00   00   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative.