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graphs      CLIMATE-UK.COM'S  REVIEW  OF  THE  BRITISH  METEOROLOGICAL  SCENE
     MONTHLY  SUMMARY
     No. 621 For   SEPTEMBER  2007
EQUAL WARMEST SEPTEMBER IN 340 YEARS OF RECORDS            DRY AND QUIET FIRST HALF, RATHER CHANGEABLE LATER. NOTABLY COLD FINISH
Text Box: High pressure was located close to southwestern Britain throughout the first half of the month with frequent northwesterly winds over UK. The second half was more changeable with southwesterlies and northwesterlies alternating, but winds veered northeasterly during the last few days. Sea-level pressure was 3 to 8 mbar above the long-term mean over the British Isles, and the anomalous flow was north to northwesterly; this was the seventh most 'northerly' September in 135 years of records.

An anticyclone centred southwest of Cornwall on the 1st drifted slowly northeast to lie close to Ireland from the 4th-12th, before declining. A new high transferred quickly eastwards across southern Britain on the 14th/15th, followed by a well-marked cold front. Winds blew from between west and north throughout this period.

The weather remained quiet and generally dry throughout the first half of the month, and although there was occasional rain in western and northern Scotland, even here amounts were trivial until the 12th. In many parts of the UK sunshine was variable rather than plentiful, but the coasts of southeast Scotland, northeast England, and southern England were well favoured, and Portland (Dorset) recorded 129h of sunshine between the 1st and 15th. The highest daily durations were 12.6h at Camborne (Cornwall) on the 4th and 12.5h at Leuchars (Fife) on the 7th. Cool and warm spells alternated: highest temperatures occurred on the 5-7th and 12th-13th, and Howden (East Yorks) registered the month’s highest reading of 25.8°C on the 7th. Coldest nights were the 3rd/4th, 10th/11th, and 14th/15th, with -2.2°C at Dalwhinnie (Inverness-shire) early on the 15th. Northern Scotland was windy on the 14th with a peak gust of 56kn at Foula (Shetland). The depression which tracked between Scotland and Iceland on the 15th contained the remnants of Tropical Storm ‘Gabrielle’, and it brought prolonged heavy rain to the highlands and islands of Scotland with 72mm at Broadford (Skye) on that day.

A brief northerly outbreak on the 17th quickly gave way to a rather changeable west to southwesterly regime from the 18th-23rd, but another very vigorous cold front swept eastwards across the UK on the 24th. A northerly flow developed in its wake, and this flow veered northeasterly as an anticyclone moved from the Atlantic across northern Scotland to reach Scandinavia on the 27th.
Text Box: The 17th was cold, and Braemar (Aberdeenshire) reported a maximum of just 7.8°C, while hail and sleet showers fell in northern Scotland, but temperatures returned to normal by the 19th, and the next few days were mostly cloudy with occasional rain, chiefly in northern and western regions where some heavy falls were logged over the hills; Capel Curig (Snowdonia) recorded 210mm in the ten days starting on the 16th. Amounts in the east and south were mostly small, and the rain that fell at Filton (nr Bristol) early on the 19th was the first measurable rain there for 31 days. It became rather warm in central and eastern districts on the 22nd and 23rd, but an active cold front brought 10-20mm of rain to much of the UK on the 24th, and the frontal passage was associated with widespread wind damage from severe squalls and a number of minor tornadoes. A gust of 58kn was recorded at Cranwell (Lincs). From the 25th-28th a cold north wind brought showers to eastern districts which gave way to longer periods of rain on the 27th-28th in East Anglia and the Southeast; meanwhile western and northern districts enjoyed long sunny spells. The 26th was particularly cold - probably the coldest September day since 1993 - with a high of 7.1°C at Braemar, 7.7°C at Carter Bar (Roxburghshire), and 10-13°C even in southern England, and the following night the mercury dropped to -3.6°C at Saughall (Ayrshire) and to -3.3C at Tyndrum (Perthshire). The last two days of the month were mostly dry and slightly warmer.

Both mean maximum and mean minimum temperature for the month were within 0.5degC of the long-term average in Scotland and Northern Ireland, and 0.5-1.0degC above in England and Wales; nevertheless, it was the coolest September for six years. Rainfall was above average in parts of northern and western Scotland also locally in northwest England and north Wales, but it was a dry September everywhere else; a swath from London to Wiltshire and Oxfordshire had less than 20mm. Sunshine totals were 20-40 per cent below normal in northern Scotland, but 10-20 per cent above in most other regions.
                                                                                                                                           
                       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 0ºC
   
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
           
                                                                     
      ºC       ºC       ºC       ºC             Hrs       Hrs         Hrs       Hrs       mm       mm         mm     mm          
                                                                                                                                           
  *Hampstead   19.0   +0.8   10.7   +0.3   24.0   05   05.4   18   00   00   00   09.2   11   131   099   1910   224   1959   072   1945   22   07.5   23   018   030   1910   157   1918   02   1959   00   00   00  
  Thorney Island   19.3   +0.1   11.1   +0.1   23.9   06   06.6   18   00   00   00   10.3   13   163   103   1958   245   1959   129   1967   19   09.8   23   033   063   1941   159   1974   02   1971   00   00   00  
  *Wattisham   18.7   +0.5   09.9   +0.4   23.4   05   06.7   30   01   00   00   10.5   04   145   101   1968   232   2003   103   1984   16   09.6   28   028   062   1960   119   1968   01   1969   00   00   00  
  *Wittering   18.3   +0.6   10.3   +0.6   22.5   05   05.5   30   00   00   00   10.3   11   152   108   1950   207   1964   093   1967   18   07.8   27   035   075   1948   132   1992   02   1959   00   00   00  
                                                                     
  Lyneham   17.9   +0.4   09.9   +0.3   22.7   05   03.2   27   01   00   00   12.3   04   159   110   1952   235   1959   100   1983   24   03.2   23   008   013   1945   142   1974   05   1959   00   00   00  
  Ross-on-Wye   19.0   +1.1   10.2   +0.5   24.0   05   04.0   18   00   00   00   11.0   15   148   114   1914   205   1929   069   1945   17   30.7   23   046   072   1859   203   1976   02   1865   00   00   00  
  *St Athan   17.8   +0.4   11.3   +0.6   21.5   07   04.8   27   00   00   02   12.4   04   153   104   1954   249   1959   074   1956   15   14.4   23   041   046   1954   223   1974   14   1959   00   00   00  
  St Mawgan   17.5   +0.4   11.9   +0.5   22.0   07   05.9   27   00   00   00   12.2   04   177   111   1945   258   1959   080   1956   12   09.0   30   029   036   1944   179   1974   10   1959   00   00   00  
                                                                     
  *Edgbaston   17.5   0.0   11.0   +0.8   22.7   06   03.5   27   00   00   00   09.7   03   115   089   1887   216   1895   067   1909   20   25.2   23   045   067   1887   165   1918   04   1959   00   00   00  
  *Valley   16.8   0.0   11.8   +0.6   20.8   06   05.4   27   00   00   03   12.2   07   118   083   1946   214   1949   096   1948   14   31.8   20   085   101   1941   174   1950   03   1986   00   00   00  
  *Woodford   17.2   +0.4   09.5   +0.3   22.6   06   -00.2   18   04   01   01   09.9   04   103   085   1945   197   1959   069   1948   13   19.6   23   073   098   1942   171   1965   05   1959   01   00   00  
  *Watnall   17.7   0.0   10.2   +0.5   23.5   06   04.7   30   01   00   00   10.0   11   129   093   1948   177   1991   075   1993   19   12.4   23   028   060   1942   147   1957   02   1959   00   00   00  
                                                                     
  *Leeming   18.2   +0.9   09.3   +0.1   24.3   06   02.5   30   05   00   00   12.0   07   125   103   1945   200   1986   073   1976   17   05.6   20   022   045   1945   174   1976   04   1959   00   00   00  
  *Boulmer   17.3   +1.0   09.8   +0.2   24.0   05   03.0   18   00   00   00   11.9   07   123   098   1945   205   1986   075   2001   14   09.4   17   033   060   1945   147   1965   12   2004   00   00   00  
  *Eskdalemuir   15.6   +0.7   07.0   -0.1   22.3   06   -02.4   18   06   01   02   11.0   10   104   104   1911   153   1959   055   1980   14   28.2   16   107   075   1911   308   1950   18   1972   00   00   00  
  *Bishopton   15.7   -0.6   09.0   +0.3   20.1   05   00.7   18   02   00   05   12.1   03   103   092   1921   169   1996   068   1965   10   13.6   16   065   068   1921   258   1985   11   1972   00   00   00  
                                                                     
  *Leuchars   16.9   +0.7   08.9   +0.2   24.4   05   01.1   15   06   00   01   12.5   07   142   111   1922   181   1997   077   1956   17   08.2   23   021   041   1922   149   1950   05   1972   00   00   00  
  *Dyce   15.5   0.0   08.8   +0.8   22.0   07   02.1   15   03   00   03   08.4   07   089   076   1941   181   2004   070   1968   11   18.0   16   068   104   1941   234   1995   15   1959   00   00   00  
  *Stornoway   14.1   -0.1   08.9   +0.2   17.8   06   02.5   18   03   00   06   10.0   30   099   093   1880   175   1903   070   1965   07   24.6   15   107   103   1943   206   1981   34   1968   00   00   00  
  *Aldergrove   16.1   0.0   10.3   +0.9   20.2   07   00.2   27   02   00   03   09.1   10   094   087   1927   177   1986   070   1962   16   09.0   16   025   031   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.