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graphs CLIMATE-UK.COM'S REVIEW OF THE BRITISH METEOROLOGICAL SCENE
MONTHLY SUMMARY
No. 669 For SEPTEMBER 2011
A RATHER CLOUDY AND CHANGEABLE MONTH, REDEEMED BY A BRILLIANT FINISH
Text Box: For much of September a disturbed southwesterly type held sway, but the month ended with an anticyclonic/southerly spell. Overall, this was the sixth most southwesterly and seventh most cyclonic September in 139 years of records. The shortage of rain in many southern, central and eastern districts was therefore a surprise, but the very wet month in northern and western parts was not.

A weak anticyclone on the 1st gave way to a southwesterly flow over the next two days, but much of England and Wales stayed dry and warm with sunny spells; Heathrow (London) reached 27.0C on the 2nd. Meanwhile outbreaks of rain affected northern and western regions, and the weather became more generally unsettled between the 4th and 14th with active depressions crossing northern Britain at intervals. One of these contained the remnants of Hurricane 'Katia' and crossed Scotland on the 12th as a vigorous feature with a central pressure close to 970 mbar. A belt of rain, heavy locally, transferred slowly east during the 4th , and the 5th was a cool, cloudy, windy day with further heavy rain in northern and western regions where Capel Curig (Caernarfon) collected 111mm in the 48h ending 2100 on the 6th. Gusts to 60kn were recorded locally in Wales, also on the 6th. The next few days were cool and breezy with widespread showers, but it became briefly drier and warmer in eastern England on the 9th/10th, though there was further rain at times elsewhere; the month's highest minimum, 18.0C, was logged at Crosby (Merseyside) early on the 10th. The 12th was a very windy day with gusts to 70kn at Capel Curig and 66kn at Lake Vyrnwy (mid-Wales) and there was prolonged heavy rain over western upslopes in Scotland; Tyndrum (Stirlingshire) collected 131mm and Cluanie Inn (Wester Ross) 88mm during the 48h ending 0900 on the 13th. The 13th brought blustery showers, but the 14th was mostly fair and cool with 11.4h sunshine at Bishopton (Renfrewshire).

A transitory anticyclone brought a quiet day on the 15th, though it was cool with the only air frost of the month at Tyndrum where the temperature fell to -0.4C. The maximum the same day at Lerwick (Shetland) was 9.6C - also the month's lowest.
Text Box: Unsettled and cool weather returned to most of the UK between the 16th and 18th as a depression drifted slowly eastwards across the country, but this was replaced by a broad southwesterly airflow from the 19th till the 26th. During this period there was further heavy rain at times in northern and western regions, with 56mm at Cluanie Inn on the 21st and 51mm at the same location on the 25th, but amounts of rain in southern, central and eastern parts were mostly small after the 20th. Temperatures rose slowly, and from the 22nd onwards it was generally rather warm.

From the 27th an anticyclonic/southerly type dominated, and it became exceptionally warm and sunny in most districts, though there was further rain at times in northwestern Scotland and more generally in northern and western parts on the 30th. The temperature reached 27.1C at Gravesend/Broadness (Kent) on the 28th, 28.8C at Kew Gardens (London) on the 29th, and 29.2C at Sutton Bonington (Notts) on the 30th. It was warm at night too, with  minima between 13 and 17C at a large number of sites.  The sun shone for 10-11h in many places on each of the last four days.

Mean maximum temperature ranged from fractionally below the 1981-2010 average in northern Scotland, to 2 degC above in East Anglia. The mean minimum was 0.8-1.2 degC above in all regions. As measured by the CET this was the warmest September since 2006. Rainfall percentages ranged from below 30 locally in the Midlands, East Anglia and Kent to around 200 in the western highlands of Scotland; smallest totals were 9mm at Cranwell (Lincs) and 11mm at Moulton Park (Northants), while the largest totals were 533mm at Cluanie Inn (Wester Ross) and 414mm at Tyndrum (Stirlingshire). Sunshine percentages ranged from below 80 in western Scotland, Northern Ireland and north Wales to around 120 in eastern England, while sunshine aggregates for the month varied between 41 hours at Kinlochewe (Wester Ross) and 72 hours at Eskdalemuir (Dumfriesshire), and 181 hours at Manston (Kent) and 180 hours at Jersey airport (Channel Is).
                                                                                                                                             
    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   20.3   +2.1   11.6   +1.2   27.9   30   01.5   26   00   00   02   09.7   29   139   001   1910   224   1959   072   1945   11   14.1   06   044   072   1910   157   1918   02   1959   00   00   00  
  *Thorney Island   19.2   0.0   13.1   +2.1   23.7   30   05.3   15   00   00   01   10.3   01   196   114   1958   245   1959   129   1967   13   08.8   04   044   083   1941   159   1974   02   1971   00   00   00  
  *Wattisham   20.6   +2.5   11.4   +1.9   26.8   30   04.1   18   00   00   01   12.3   01   177   123   1968   232   2003   103   1984   13   02.6   04   014   030   1960   119   1968   01   1969   00   00   00  
  *Wittering   20.4   +2.7   11.1   +1.4   28.4   30   06.5   15   00   00   00   12.3   01   154   110   1950   207   1964   093   1967   21   12.8   04   029   062   1948   132   1992   02   1959   00   00   00  
                                                                     
  *Lyneham   18.9   +1.4   11.5   +1.9   26.3   29   05.5   15   00   00   02   11.3   28   137   095   1952   235   1959   100   1983   11   11.6   20   052   080   1945   142   1974   05   1959   01   00   00  
  Ross-on-Wye   20.2   +2.3   11.0   +1.3   27.1   30   04.7   01   00   00   00   08.9   01   131   100   1914   205   1929   069   1945   11   04.9   05   033   051   1859   203   1976   02   1865   00   00   00  
  *St Athan   18.4   +1.0   12.9   +2.2   24.4   29   06.6   15   00   00   01   11.0   14   121   082   1954   249   1959   074   1956   09   10.4   20   085   095   1954   223   1974   14   1959   00   00   00  
  *Culdrose   17.3   +0.4   12.8   +1.8   21.6   28   07.5   23   00   00   01   10.0   29   132   084   1961   212   1972   098   1983   08   09.0   20   047   057   1961   185   1974   23   2001   00   00   00  
                                                                     
  *Edgbaston   19.2   +1.7   11.7   +1.5   27.1   30   07.9   15   00   00   00   10.5   01   158   126   1887   216   1895   067   1909   12   07.4   10   029   043   1887   165   1918   04   1959   00   00   00  
  *Valley   17.1   +0.3   12.7   +1.5   22.6   28   07.9   04   00   00   03   11.4   01   108   075   1946   214   1949   096   1948   11   15.6   21   091   110   1941   174   1950   03   1986   00   00   00  
  *Woodford   18.7   +1.9   11.0   +1.8   26.8   30   05.7   01   01   00   01   11.1   28   124   101   1945   197   1959   069   1948   10   07.6   06   038   051   1942   171   1965   05   1959   00   00   00  
  *Watnall   19.8   +2.1   11.4   +1.7   28.9   30   06.4   18   00   00   02   10.9   28   145   103   1948   177   1991   075   1993   13   08.0   10   030   063   1942   147   1957   02   1959   00   00   00  
                                                                     
  *Leeming   18.7   +1.4   10.3   +1.1   27.1   30   03.1   15   02   00   01   10.4   15   121   100   1945   200   1986   073   1976   16   11.6   16   028   056   1945   174   1976   04   1959   00   00   00  
  *Boulmer   17.7   +1.4   10.4   +1.1   24.6   28   06.5   15   00   00   02   11.7   14   146   114   1945   205   1986   075   2001   11   08.4   05   034   062   1945   147   1965   12   2004   00   00   00  
  *Eskdalemuir   15.2   +0.3   08.4   +1.3   22.5   30   00.3   15   01   00   08   10.7   15   072   072   1911   153   1959   046   2008   04   36.8   11   236   165   1911   308   1950   18   1972   00   00   00  
  *Bishopton   16.3   0.0   10.2   +1.5   22.8   28   02.8   15   00   00   02   11.4   15   104   092   1921   169   1996   058   2008   05   25.2   25   172   180   1921   258   1985   11   1972   00   00   00  
                                                                     
  *Leuchars   17.4   +1.2   09.6   +0.9   24.1   28   06.0   04   00   00   01   10.1   28   130   101   1922   181   1997   077   1956   11   11.4   04   060   118   1922   149   1950   05   1972   00   00   00  
  *Dyce   16.9   +1.4   10.0   +2.0   23.9   30   04.8   16   01   00   02   09.7   04   114   097   1941   181   2004   070   1968   11   23.6   16   090   138   1941   234   1995   15   1959   00   00   00  
  *Stornoway   15.0   +0.8   10.4   +1.7   19.2   28   06.5   15   00   00   05   10.3   15   078   072   1880   175   1903   065   2009   03   18.8   12   143   139   1943   206   1981   34   1968   00   00   00  
  *Aldergrove   16.8   +0.7   11.2   +1.8   21.9   28   05.9   15   00   00   01   09.2   28   090   082   1927   177   1986   070   1962   06   27.4   30   113   142   1927   163   1981   06   1986   00   00   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative.