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graphs CLIMATE-UK.COM'S REVIEW OF THE BRITISH METEOROLOGICAL SCENE
MONTHLY SUMMARY
No. 681 For SEPTEMBER 2012
QUITE DRY FOR THREE WEEKS ESPECIALLY IN EAST ANGLIA AND THE SOUTHEAST; PROLONGED HEAVY RAIN 23RD-25TH
Text Box: Mean sea-level pressure was above average in mid-Atlantic but below average over Scandinavia and the Norwegian Sea. The anomalous flow over the British Isles was weakly northwesterly.

Pressure was relatively high over southern Britain until the 9th, but a changeable west to southwesterly flow affected the northern half of the country. The first two days of the month were rather cloudy and there was some sporadic rain, chiefly in northwest Scotland on the 1st. It became warm and sunny over England and Wales on the 3rd and 4th with highs of 24-26C in East Anglia and the Southeast but northern and western Scotland remained changeable and rather windy. The 5th and 6th were mostly sunny though rather cooler, while the 7th was the sunniest day of the month with 12.5h at East Malling (Kent) and Whipsnade (Beds). Temperatures climbed again over the next three days, reaching 29.3C at Writtle (Essex) and Cambridge on the 9th. Although these were the highest September readings for six years, a higher maximum was obtained last year on October 1. The night of 9th/10th was notably warm, too, with a minimum of 17.0C at Eastbourne (Sussex).

A changeable westerly flow lasted from the 10th till the 20th, though pressure was quite high at times over southern districts. A polar airflow was responsible for a sudden drop in temperature on the 11th; highs were typically 14-18C over England and Wales, but just 8.5C at Dalwhinnie (Inverness-shire). A small but active disturbance brought short-lived bursts of rain to central and southern districts later on the 12th, and at some places in southern Britain this was the only significant rain during the first three weeks of September. By contrast, heavier rain - often orographically enhanced - fell frequently in western and northern districts, notably on the 13th with 62mm at Cluanie Inn (Wester Ross). This day was also windy, with gusts to 61kn at Lerwick (Shetland). Slight ground frosts occurred quite widely early on the 11th, 12th, 13th, 18th and 19th.
Text Box: A small anticyclone developed over the UK on the 21st and 22nd but this moved away quickly the next day as a deepening depression, spawned by former tropical storm "Nadine", moved northwards across Biscay, crossing England and Wales on the 24th and 25th. Central pressure dipped to 973 mbar at its lowest. The weather remained cool on the 21st and 22nd although it became mostly dry with sunny spells, and there was local air frost at night in Scotland. Heavy rain spread northwards across the country the next day; highest daily totals to hand were 65mm at Credenhill (Herefs) on the 23rd and 98mm at Ravensworth (N.Yorks) on the 24th. Over the three-day period 23rd-25th as much as 131mm fell at Ravensworth, with over 100mm in other parts of Yorkshire, Durham, Northumberland, Cumbria, Glamorgan, Down and Antrim. A good deal of flooding ensued. It was particularly cool during this period with a minimum of -4.1C at Braemar (Aberdeenshire) on the 23rd, and maxima of 7.7C at Tredegar (Monmouthshire) on the 23rd and 8.3C at Banagher (Londonderry) on the 24th. A northeasterly gale affected Scotland on the 25th with a maximum gust of 63kn at Inverbervie (Kincardineshire). A westerly regime during the last five days of September resulted in the re-establishment of cool and changeable weather.

It was the coolest September, averaged nationally, since 1994. Following the warm start maximum temperature (averaged over England and Wales) every day from the 11th onwards was below the seasonal average. Monthly mean temperature in all regions was between 0.5 and 1.5 degC below the 1981-2010 normal. Rainfall percentages varied widely: from 250 locally in northeast England to around 50 locally in northeast and central Scotland and also at a few locations in southern England. It was, perhaps surprisingly, a rather sunny month with totals ranging from 5 per cent above normal in western Scotland to 35 per cent above in East Anglia. Over England and Wales it was the sunniest September since 2003.
                                                                                                                                             
    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   19.0   +0.4   09.7   -1.1   28.0   08   04.8   22   00   00   01   09.5   05   147   108   1910   224   1959   072   1945   17   28.8   23   061   106   1910   157   1918   02   1959   00   00   00  
  *Thorney Island   18.3   -1.3   10.0   -1.4   23.7   04   05.0   30   00   00   01   11.5   07   181   112   1958   245   1959   129   1967   11   34.2   23   076   152   1941   159   1974   02   1971   00   00   00  
  *Wattisham   18.6   +0.1   08.5   -1.4   27.6   09   04.0   30   00   00   03   12.4   07   182   124   1968   232   2003   103   1984   13   18.0   23   048   111   1960   119   1968   01   1969   01   00   00  
  *Wittering   18.1   0.0   08.7   -1.4   27.3   09   04.4   19   00   00   04   11.4   05   164   114   1950   207   1964   093   1967   21   23.8   23   048   110   1948   132   1992   02   1959   01   00   00  
                                                                     
  *Lyneham   17.1   -0.8   09.0   -1.0   23.9   09   04.1   22   01   00   02   12.1   07   166   112   1952   235   1959   100   1983   12   30.0   23   069   113   1945   142   1974   05   1959   00   00   00  
  Ross-on-Wye   18.4   +0.1   08.3   -1.8   24.8   07   02.6   22   01   00   00   10.0   07   158   118   1914   205   1929   069   1945   18   59.0   23   074   123   1859   203   1976   02   1865   00   00   00  
  *St Athan   16.7   -1.1   10.5   -0.6   19.8   04   06.0   22   00   00   02   11.9   05   135   090   1954   249   1959   074   1956   10   41.6   23   107   127   1954   223   1974   14   1959   00   00   00  
  *Culdrose   16.7   -0.6   11.1   -0.3   19.8   08   04.2   22   00   00   02   11.8   06   154   096   1961   212   1972   098   1983   13   16.0   23   046   060   1961   185   1974   23   2001   00   00   00  
                                                                     
  *Edgbaston   17.1   -0.8   09.5   -1.1   24.3   09   03.9   22   00   00   00   10.8   07   167   131   1887   216   1895   067   1909   17   39.4   23   071   114   1887   165   1918   04   1959   00   00   00  
  *Valley   15.9   -1.3   11.4   -0.2   18.8   09   03.5   22   01   00   05   10.5   05   135   092   1946   214   1949   096   1948   07   43.2   24   112   144   1941   174   1950   03   1986   00   00   00  
  *Woodford   16.1   -1.1   08.7   -0.9   23.3   08   00.5   22   02   00   03   09.4   22   126   101   1945   197   1959   069   1948   08   31.7   24   099   141   1942   171   1965   05   1959   00   00   00  
  *Watnall   17.3   -0.8   09.0   -1.1   25.7   09   04.7   22   00   00   03   11.5   07   149   104   1948   177   1991   075   1993   17   20.4   24   064   145   1942   147   1957   02   1959   01   00   00  
                                                                     
  *Leeming   17.0   -0.7   08.4   -1.2   24.3   09   00.0   22   03   00   04   10.6   22   136   109   1945   200   1986   073   1976   16   76.4   24   122   266   1945   174   1976   04   1959   00   00   00  
  *Boulmer   16.2   -0.5   09.7   0.0   21.8   03   02.5   23   01   00   03   09.7   19   144   109   1945   205   1986   075   2001   10   23.8   24   084   162   1945   147   1965   12   2004   00   00   00  
  *Eskdalemuir   14.0   -1.3   07.1   -0.4   17.9   02   -01.8   22   04   02   05   09.9   22   091   089   1911   153   1959   046   2008   06   25.2   20   169   127   1911   308   1950   18   1972   00   00   01  
  *Bishopton   15.0   -1.7   08.9   -0.2   18.8   03   00.2   22   03   00   05   10.7   21   115   100   1921   169   1996   058   2008   04   14.8   29   099   111   1921   258   1985   11   1972   00   00   00  
                                                                     
  *Leuchars   16.1   -0.5   08.3   -0.8   22.7   03   -00.5   23   05   01   04   11.3   04   155   118   1922   181   1997   077   1956   14   10.2   25   046   097   1922   149   1950   05   1972   00   00   00  
  *Dyce   16.2   +0.3   08.3   -0.1   25.2   03   -00.1   23   04   01   03   11.5   08   135   113   1941   181   2004   070   1968   11   18.2   24   055   091   1941   234   1995   15   1959   00   00   00  
  *Stornoway   13.7   -0.9   08.7   -0.4   17.4   02   02.3   22   01   00   05   07.1   05   098   089   1880   175   1903   065   2009   05   18.4   13   131   137   1943   206   1981   34   1968   00   00   00  
  *Aldergrove   15.7   -0.8   09.6   -0.2   20.9   03   01.2   22   01   00   03   09.4   23   114   103   1927   177   1986   070   1962   08   31.0   24   074   099   1927   163   1981   06   1986   00   00   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative.      
  Values for Woodford are estimated.      
  Averages are for 1981-2010