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graphs      CLIMATE-UK.COM'S  REVIEW  OF  THE  BRITISH  METEOROLOGICAL  SCENE
     MONTHLY  SUMMARY
     No. 648 For   DECEMBER  2009
        MILD UNSETTLED START; VERY COLD WITH FREQUENT SNOW FROM MID-MONTH ONWARDS
Text Box: Although December will be remembered for the very cold and wintry spell which set in around mid-month, the first ten days saw a continuation of November’s very disturbed but rather mild weather with little snow and few night frosts. The mean monthly pressure field shows the Icelandic low displaced far south of its normal position, an absent Azores anticyclone, and high pressure over Greenland and northwest Russia. The anomalous flow over the British Isles was easterly, and it was the 15th most ‘easterly’ December in 137 years of records.

After a sharp early frost with -9.0°C at Cromdale (Strathspey), heavy rain and strong winds crossed the country on the 1st, with 31mm falling at Machrihanish (Kintyre). After a brief interlude of somewhat quieter weather, wet and windy conditions returned between the 4th and the 7th, with four-day rainfall totals of 94mm at Shap (Cumbria) and 85mm at Capel Curig (Snowdonia); Capel Curig also recorded the month’s highest wind gust of 57kn on the 7th. The temperature climbed to 13.6°C at Jersey airport on the 5th, and to 13.4°C at Eastbourne on the 9th.

After six weeks dominated by low pressure, a complete change occurred around the 10th, and there followed several days with high pressure in charge. This spell was rather cold but quiet, with night frosts and widespread fog, but many places enjoyed sunny days, York recording 7.4h of bright sunshine on the 10th, and Manchester 7.3h on the 11th. The 14th-16th were much duller with persistent light rain and snow as small disturbances tracked south and then southwest across the country.

A very cold north-easterly flow set in on the 17th, and the first of a series of heavy snowfalls struck East Anglia, the east Midlands, and Southeast England that night, leaving 25cm level snow on the ground in west Norfolk, and 10-20cm in many other places. Transport networks were severely disrupted, and the Channel Tunnel was closed for several days. The temperature fell close to -14°C at Topcliffe (N Yorks) early on both Text Box: the 19th and 20th. Further heavy snow hit many parts of the Home Counties on the afternoon/evening of the 21st, adding as much as 15cm new snow over the Chilterns, and again bringing chaos on the roads and at airports. Heavy snow also affected many parts of Scotland, northern England and Northern Ireland between the 20th and 24th with an aggregate depth of 23cm at Aviemore (Inverness-shire) on the 23rd. Warmer air advancing across southern England was preceded by widespread freezing rain on the 23rd, and thunderstorms and heavy hail were reported in many places. More localised freezing rain recurred in parts of the West Country on the 24th.

The cold weather relaxed its grip in the southern half of Britain over Christmas, but in Scotland, Northern Ireland and northern England it became even colder, and there were renewed snowfalls in these areas. At Aberfeldy (Perthshire) snow lay 40cm deep on the 29th. Temperatures in the highlands dropped to -14°C or below on each morning from the 22nd to the 30th, and remained below -10°C by day and by night on the 26th, 28th and 29th. Braemar (Aberdeenshire) was coldest with a minimum of -18.4°C early on the 29th, and a maximum that afternoon of -12.2°C. St Mary’s (Isles of Scilly) reached 12.0°C the same day, and the southern half of the UK had prolonged heavy rain, with sleet or wet snow in parts of the Midlands, north Wales and northern England. Snow showers returned to many eastern and central parts of the UK on the 31st as the cold north-easterly flow strengthened once again.

Although the first part of the month was mild, the cold spell after mid-month was sufficient to make this the coldest December since 1996, with regional temperatures ranging from 1.5degC below the 1971-2000 normal in southern England to 3.0degC below in eastern Scotland. Rainfall was 30-50 per cent above normal in parts of the Midlands and Southeast England, but 30-50 per cent below over much of Scotland and Northern Ireland. Sunshine duration, averaged nationally, was almost 60 per cent above normal, but several recent Decembers have been similarly sunny.
                                                                                                                                             
                       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   05.7   -2.0   01.6   -0.8   11.2   09   -04.4   19   16   10   04   06.3   10   076   168   1910   086   2001   008   1956   07   13.2   29   089   144   1910   175   1914   10   1933   00   07   02  
  Thorney Island   07.3   -1.3   02.4   -1.3   12.6   09   -04.3   23   15   10   05   07.6   20   084   152   1958   114   2001   037   1966   08   22.2   29   100   137   1941   165   1993   19   1953   01   03   01  
  *Wattisham   05.0   -1.5   01.1   -1.7   11.5   06   -05.8   23   17   11   07   06.9   10   063   125   1979   082   2008   022   2002   03   13.4   29   070   134   1964   120   1965   24   1988   00   11   03  
  *Wittering   05.0   -1.5   00.9   -1.7   10.3   06   -08.2   20   14   11   09   06.8   10   081   163   1950   082   2001   020   1956   03   11.6   29   060   111   1948   130   1978   07   1963   00   11   02  
                                                                     
  Lyneham   05.2   -2.0   01.1   -1.7   10.8   09   -07.2   19   16   11   12   07.0   20   056   113   1952   083   2001   017   1956   13   16.0   07   089   122   1945   159   1959   16   1988   00   08   03  
  Ross-on-Wye   06.2   -1.2   00.3   -3.1   12.5   05   -06.5   22   23   14   11   06.2   20   051   105   1915   078   1948   012   1989   10   14.0   29   074   104   1859   197   1929   11   1991   00   09   01  
  *St Athan   06.8   -1.2   02.5   -1.6   12.3   09   -04.6   19   18   07   09   05.7   10   061   132   1954   072   2008   003   1956   08   11.4   05   080   085   1954   208   1965   31   1988   00   05   00  
  Culdrose   08.6   -1.0   04.0   -2.1   12.4   05   -06.2   19   18   07   09   06.5   17   * 088   169   1961   080   2001   021   1988   07   30.0   07   113   100   1961   246   1978   27   1975   00   02   00  
                                                                     
  *Edgbaston   04.9   -2.5   01.5   -1.8   10.1   05   -04.1   20   20   11   04   05.4   20   062   142   1887   090   1891   005   1890   13   12.6   05   056   077   1887   166   1965   10   1926   00   10   02  
  *Valley   07.4   -1.5   03.2   -2.2   11.8   09   -01.8   28   15   06   08   06.1   12   043   087   1946   080   1960   025   1998   05   19.4   06   087   095   1941   179   1964   17   1963   00   11   01  
  *Woodford   05.4   -1.4   00.3   -2.0   10.9   09   -09.4   22   20   12   08   06.6   21   066   146   1945   075   2001   016   1947   05   08.8   03   071   090   1942   180   1965   11   1963   00   03   00  
  *Watnall   05.1   -1.4   01.4   -1.2   10.1   07   -05.7   20   17   12   10   06.8   10   * 078   156   1948   075   2001   012   1956   06   15.6   05   074   138   1941   180   1965   19   1963   00   09   01  
                                                                     
  *Leeming   04.8   -2.2   -00.6   -2.9   09.8   09   -10.4   19   19   16   09   05.9   04   059   139   1945   077   1967   014   1972   02   08.6   05   079   132   1945   125   1978   16   1988   00   11   02  
  *Boulmer   05.6   -1.3   01.5   -0.9   10.8   09   -04.0   20   18   12   07   05.7   04   057   126   1945   082   2006   021   2002   06   07.6   16   061   102   1945   205   1978   17   1975   00   09   00  
  *Eskdalemuir   03.0   -2.4   -01.8   -2.6   08.9   09   -09.0   19   24   20   12   05.6   28   031   084   1911   074   1967   003   1912   10   22.6   05   105   066   1911   351   1993   33   1933   00   15   01  
  *Bishopton   03.7   -3.5   -00.8   -3.0   09.6   09   -09.3   24   26   16   10   03.5   16   034   105   1921   072   2001   009   1956   09   16.4   04   073   068   1921   295   2006   15   1933   00   10   00  
                                                                     
  *Leuchars   04.3   -2.4   -01.2   -3.3   10.2   09   -09.3   29   25   18   09   05.5   04   039   076   1921   082   1967   016   1934   09   16.8   26   067   106   1921   155   1978   08   1926   00   09   00  
  *Dyce   04.5   -1.9   -00.5   -2.0   09.0   14   -09.2   27   19   18   11   05.2   28   037   082   1941   088   2006   016   2002   09   14.2   24   082   102   1941   160   1978   20   1991   00   13   00  
  *Stornoway   06.7   -0.8   02.4   -0.9   10.3   08   -02.3   28   19   11   11   05.1   12   032   129   1880   057   1995   006   1884   06   25.2   02   116   093   1943   222   1985   29   1977   00   10   00  
  *Aldergrove   05.6   -1.5   01.1   -1.8   11.0   05   -06.7   24   22   10   09   05.8   15   061   174   1927   077   2001   017   1954   09   14.2   04   053   059   1927   195   1978   15   1963   00   05   00  
                                                                     
                                                                                                                                             
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative. Thorney Island's   * New high record    
  sunshine figures are made at a nearby site.