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graphs CLIMATE-UK.COM'S REVIEW OF THE BRITISH METEOROLOGICAL SCENE
MONTHLY SUMMARY
No. 657 For SEPTEMBER 2010
A CHANGEABLE MONTH WITH A COLD LAST WEEK; HEAVY RAIN IN NORTHERN IRELAND 6TH/7TH
Text Box: September 2010 was an episodic month with a succession of weather types, none of which lasted as long as a week. On the mean monthly chart, a brisk westerly flow across the Atlantic between latitudes 40 and 60 degN became a markedly diffluent southwesterly flow across the British Isles. Mean sea-level pressure anomaly ranged from +3mbar in Shetland to -2mbar in Cornwall and southwest Ireland.

An anticyclone over the UK on the 1st drifted slowly to Scandinavia over the next few days, allowing a southeasterly flow to develop while weak fronts affected western districts. The weather remained fine until the 3rd with cool nights and rather warm days; Kinloss (Morayshire) logged 13.2h bright sunshine on the 2nd while the temperature reached 24.5C at Kinlochewe (Wester Ross) on the 3rd. The 4th and 5th were cloudier with a freshening breeze, and western districts had occasional rain.

A vigorous depression moved north across Ireland on the 6th-7th, and the associated frontal zone crossed the whole of the UK, preceded by strong easterly winds, and it brought widespread rain which was heavy in Northern Ireland, northwest England and southwest Scotland; largest totals occurred in Northern Ireland where Lough Fea (Co Tyrone) collected 107mm and Killowen (Co Down) 102mm in the 60h to 09GMT on the 7th. Showers, locally heavy and thundery, followed the general rain. A southwesterly flow brought a succession of fronts from late on the 9th till the 11th; little rain fell in southern England, but there were heavy falls in south and mid Wales, with 73mm falling in 36h at Sennybridge (Breconshire). A transitory ridge gave England and Wales a fairly sunny day on the 12th, but further Atlantic fronts crossed the country on the 13th and 14th accompanied by strong winds and heavy orographic rain; 100mm fell in 48h at Cluanie Inn in Glen Shiel (Wester Ross). From the 15th to the 17th a strong, cold, northwesterly flow covered the country, bringing showers and sunny intervals; the month's highest gust of 59kn was recorded at Capel Curig (Caernarfon) on the 15th, while a high of just 9.2C was logged at Loch Glascarnoch (Wester Ross) on the 17th.
Text Box: A moderate southwesterly flow returned on the 18th-19th, delivering copious amounts of rain to western and northern districts with 68mm in 48h at both Stonyhurst (Lancs) and Capel Curig, but little rain fell in southern, midland and eastern counties of England. A southerly airstream developed between the 20th and 22nd, and it became fine and warm in central and eastern England with 24.6C recorded at Gravesend/ Broadness (Kent) on the 22nd. But western districts were less settled, and Bishopton (Renfrewshire) collected 60mm of rain on the same day. 

Heavy showers and thunderstorms in association with a southeastward-moving depression affected many places on the 23rd, but strong northerly winds developed between the 24th and 27th and there were further outbreaks of rain in eastern counties. It became cold; the lowest maximum was 7.6C at Braemar on the 24th, but highs of 10-12C in southern and central England on both the 24th and 26th were the lowest in September at several sites since 1994. Tyndrum (Stirlingshire) and Kinbrace (Sutherland) reported minima of -4.4C on the 26th and 27th respectively - the lowest anywhere in the UK in September since 1993. Further rain, heavy at times, spread slowly from west to east during the 28th and 29th, followed by a brighter day on the 30th.

Both mean maximum and mean minimum temperatures were between zero and 1.0degC above the 1971-2000 mean in all regions. Rainfall was within 40 per cent of the average over much of the country, but southern counties from Dorset to Sussex were dry with less around half the normal rainfall, while parts of eastern Scotland and northeast England had twice the average. Some places in Northern Ireland also had almost twice the normal. Sunshine duration ranged from 10-20 per cent above normal in northern and western Scotland to 5-10 per cent below locally in the Midlands, East Anglia and the Southeast, monthly totals ranging from 80h at Braemar (Aberdeenshire) to 190h 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   18.0   -0.2   10.6   +0.2   22.7   09   04.3   30   00   00   00   09.8   09   105   078   1910   224   1959   072   1945   09   12.8   22   049   080   1910   157   1918   02   1959   01   00   00  
  *Thorney Island   18.3   -0.9   11.3   +0.3   21.1   16   04.9   30   00   00   01   11.4   16   137   087   1958   245   1959   129   1967   14   13.2   22   052   097   1941   159   1974   02   1971   00   00   00  
  *Wattisham   17.9   -0.2   10.1   +0.6   22.3   21   02.6   11   00   00   01   10.1   09   121   084   1968   232   2003   103   1984   09   13.6   25   058   124   1960   119   1968   01   1969   02   00   00  
  *Wittering   18.1   +0.4   10.2   +0.5   22.7   09   04.9   30   00   00   02   11.7   22   129   091   1950   207   1964   093   1967   08   15.4   25   057   121   1948   132   1992   02   1959   02   00   00  
                                                                     
  *Lyneham   18.0   +0.5   10.0   +0.4   21.7   16   02.9   30   00   00   03   12.5   16   134   092   1952   235   1959   100   1983   08   09.6   22   051   079   1945   142   1974   05   1959   02   00   00  
  Ross-on-Wye   18.4   +0.5   10.1   +0.4   22.6   15   03.0   30   00   00   01   10.7   28   121   093   1914   205   1929   069   1945   07   13.6   25   045   070   1859   203   1976   02   1865   01   00   00  
  *St Athan   17.8   +0.4   11.3   +0.6   21.5   15   04.2   30   00   00   02   12.0   30   145   099   1954   249   1959   074   1956   12   09.4   25   048   053   1954   223   1974   14   1959   00   00   00  
  *Culdrose   17.2   +0.2   11.6   +0.6   19.6   15   05.3   30   00   00   02   10.7   30   142   090   1961   212   1972   098   1983   07   26.6   25   089   107   1961   185   1974   23   2001   00   00   00  
                                                                     
  *Edgbaston   17.3   -0.2   10.7   +0.5   20.9   17   04.6   30   00   00   01   09.5   16   103   082   1887   216   1895   067   1909   12   11.8   25   049   073   1887   165   1918   04   1959   02   00   00  
  *Valley   17.3   +0.5   12.0   +0.8   22.4   15   05.1   30   00   00   01   12.4   15   130   091   1946   214   1949   096   1948   18   22.8   19   093   111   1941   174   1950   03   1986   00   00   00  
  *Woodford   17.4   +0.6   09.4   +0.2   21.2   20   -00.2   30   01   01   03   11.9   16   117   095   1945   197   1959   069   1948   08   15.2   12   090   119   1942   171   1965   05   1959   01   00   00  
  *Watnall   17.8   +0.1   10.4   +0.7   22.0   16   04.7   30   00   00   01   11.5   16   109   077   1948   177   1991   075   1993   12   28.0   09   067   141   1942   147   1957   02   1959   02   00   00  
                                                                     
  *Leeming   18.1   +0.8   10.0   +0.8   22.1   20   03.1   27   00   00   01   11.7   24   126   104   1945   200   1986   073   1976   13   16.0   07   058   118   1945   174   1976   04   1959   01   00   00  
  *Boulmer   16.5   +0.2   10.7   +1.4   22.1   20   06.3   25   00   00   01   09.3   26   124   096   1945   205   1986   075   2001   13   11.2   23   057   103   1945   147   1965   12   2004   00   00   00  
  *Eskdalemuir   15.9   +1.0   07.9   +0.8   20.7   15   -00.2   27   02   01   03   10.0   30   097   097   1911   153   1959   046   2008   12   29.6   19   152   106   1911   308   1950   18   1972   00   00   01  
  *Bishopton   16.9   +0.6   09.5   +0.8   21.7   15   01.6   30   00   00   01   11.7   30   135   120   1921   169   1996   058   2008   09   59.6   23   185   193   1921   258   1985   11   1972   00   00   00  
                                                                     
  *Leuchars   16.4   +0.2   09.4   +0.7   21.3   20   03.3   30   00   00   01   11.2   30   142   111   1922   181   1997   077   1956   09   32.2   24   114   222   1922   149   1950   05   1972   00   00   00  
  *Dyce   14.9   -0.6   09.3   +1.3   20.8   20   02.1   27   00   00   01   10.4   19   098   083   1941   181   2004   070   1968   09   30.0   23   091   139   1941   234   1995   15   1959   00   00   00  
  *Stornoway   14.8   +0.6   09.8   +1.1   20.5   09   03.0   26   01   00   05   12.9   19   104   096   1880   175   1903   065   2009   11   20.2   16   129   124   1943   206   1981   34   1968   00   00   00  
  *Aldergrove   16.8   +0.7   10.8   +1.4   21.5   15   02.9   30   00   00   00   11.6   15   102   093   1927   177   1986   070   1962   11   26.2   16   110   136   1927   163   1981   06   1986   00   00   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative. Thorney Island's      
  sunshine figures are made at a nearby site.