December 2009
A Dartmoor winter scene. Wild, moody and mesmerising.
A Dartmoor December scene. Wild, moody and mesmerising.
Summary for  December 2009
Mean Max: 6.8ºC (-2.3ºC)
Mean Min: 0.8ºC (-2.7ºC)
Mean: 3.8ºC (-2.5ºC)
     
High Max: 12.1ºC 9th
Low Max: 1.2ºC 18th
High Min: 7.2ºC 6th
Low Min: -7.2ºC 19th
Mean Grass Min: -3.3ºC  
Grass Min: -10.3ºC 19th
     
Rain Total (gauge): 86.3 mm (89%)
Rain Total (tipping bucket): 73.2 mm (76%)
Rain Days >0.2 mm: 21 Days  
Rain Days >1.0 mm: 17 Days  
Max 24 hrs: 12.4 mm 6th
Days without any rain: 10  
     
Air Frost: 12 Days  
Ground Frost: 24 Days  
Snow Falling: 0 Days  
Snow (50%) @ 9am: 0 Days  
Thunder Heard: 0 Days  
Hail <5 mm: 0 Days  
Hail >5 mm: 0 Days  
Fog @ 9am: 0 Days  
     
Total Monthly Sunshine: 98h:43m  
Total Monthly Sunshine: 98.7 Hours  
Most Sunshine in a Day: 07h:28m 25th
Average Daily Sunshine: 03h:11m  
Sunless Days: 6 Days  
Cloudless Days: 4 Days  
Total Possible Sunshine: 249h:24m  
Percentage of Total Sun: 40%  
     
Mean Soil Temp @ 30 cm: 5.2ºC  
Min Soil Temp @ 30 cm: 2.2ºC 23rd
Max Soil Temp @ 30 cm: 8.0ºC 6th
Mean Soil Temp @ 100 cm: 8.1ºC  
Min Soil Temp @ 100 cm: 5.7ºC 29th
Max Soil Temp @ 100 cm: 10.3ºC 1st
     
Mean 10 Min Wind >39 mph: 0.00 Days  
N: 5.28 Days  
NE: 6.07 Days  
E: 2.19 Days  
SE: 3.02 Days  
S: 3.41 Days  
SW: 3.26 Days  
W: 2.94 Days  
NW: 1.25 Days  
Calm: 3.58 Days  
Mean Wind: 3.1 mph  
Max Gust: 33 mph 7th
     
Mean Cloud Cover: 62%  
Mean RH @ 9am: 89%  
Rain Duration >0.1mm/hour: 51.3 Hours  
Frost Duration: 127.3 Hours  
Max Frost Duration in a Day: 18.0 Hours 22nd
     
Mean Sea Temperature: 9.9ºC  
Normal for Month:    
Max Sea Temperature: 11.6ºC 1st
Min Sea Temperature: 8.1ºC 28th
     
Mean Pressure @ 9am: 1007.7 hPa (-6.9 hPa)
Mean Pressure: 1006.1 hPa (-8.5 hPa)
Max Pressure: 1032.6 hPa 12th
Min Pressure: 985.1 hPa 22nd
     
Max Dewpoint: 10.7ºC 9th
Min Dewpoint: -9.4ºC 19th
Mean Dewpoint: 1.4ºC  
     
Max Humidity: 94% 9th
Min Humidity: 70% 18th
Mean Humidity: 87% (-0)

 

A cold, generally unsettled month though rather sunny at times.

Night time and daytime temperatures were well below the average and there were a very high number of air and ground frosts.
Overall rainfall was slightly below the long term average even though there were a high number of days when rain actually fell.
A very unthundery month though this is not uncommon for December.
Sunshine levels were above average even though there were 6 days when the sun did not shine at all.
Soil temperatures were generally around normal though they ended up being below normal during the final week.
Winds were dominant from the north & north-east sectors.
There were 127 hours of frost, this is the highest recorded monthly number of hours in over 5 years.
Sea temperatures gradually fell through the month and ended up slightly below average.
Mean pressure was below normal and indicative of the generally unsettled nature of this month.
Dewpoints were well below normal for most of the month.
Despite the cold, dry air, the RH ended up being around average.
Weather Data for Otter Valley, Devon.  December 2009  
  Temp (oC) Hum (RH%) Dewpoint (oC) Wind (mph) Rain Pressure (hPa) Grass Sun  
  Min Max Ave Min Max Ave Min Max Ave Max Ave Run mm Min Max Ave Min Hours Observations
1 -3.2 7.8 2.3 73 91 82 -5.1 6.1 0.5 27 3.3 79 2.6 1003 1015 1009 -3.6 0.2 Sunny ints am, cloudy pm
2 4.4 9.6 7.0 90 92 91 2.7 7.8 5.3 22 2.6 63 3.7 991 1015 1003 -0.6 0.8 Showers all day
3 4.1 7.5 5.8 73 92 83 -1.0 5.9 2.5 32 4.3 103 2.0 992 1005 999 -1.8 3.3 Showers all day
4 -2.9 9.6 3.4 85 93 89 -4.7 8.1 1.7 14 0.8 18 1.7 1002 1011 1006 -6.4 0.3 Frosty am, drizzle pm
5 5.1 11.6 8.4 87 93 90 3.1 9.8 6.5 27 4.8 116 3.3 995 1002 998 0.1 0.6 Sunny ints am, cloudy pm
6 7.2 12.0 9.6 72 93 83 3.3 10.5 6.9 31 8.3 199 12.4 989 1003 996 2.5 4.9 Sunny intervals all day
7 5.9 10.2 8.1 80 89 85 2.7 7.7 5.2 33 6.3 151 5.7 995 1003 999 -2.3 1.3 Showers am, sunny ints pm
8 2.1 11.9 7.0 83 93 88 0.1 10.3 5.2 19 2.5 59 6.1 1002 1011 1007 -2.7 0.0 Rain, intermittent all day
9 5.4 12.1 8.8 92 94 93 3.9 10.7 7.3 9 0.9 22 0.0 1011 1020 1015 0.5 2.7 Sunny intervals all day
10 2.3 9.6 6.0 91 93 92 0.7 8.0 4.4 14 0.8 20 1.1 1020 1032 1026 -2.1 5.8 Sunny intervals all day
11 2.2 7.0 4.6 87 92 90 0.4 5.0 2.7 18 2.1 51 0.0 1031 1032 1031 -2.6 3.9 Sunny intervals all day
12 2.8 7.3 5.1 82 92 87 0.9 4.5 2.7 18 4.7 114 0.0 1030 1033 1031 -1.9 7.2 Sunny all day
13 2.6 6.6 4.6 80 90 85 0.6 3.2 1.9 21 4.8 114 0.0 1026 1031 1029 -1.9 6.8 Sunny intervals all day
14 2.2 5.6 3.9 86 89 88 0.2 3.4 1.8 15 1.9 46 0.0 1021 1026 1023 -0.6 0.0 Dull all day
15 2.2 7.1 4.7 89 92 91 0.2 4.2 2.2 15 0.7 17 0.2 1016 1021 1018 -5.2 0.0 Dull am, drizzle pm
16 -2.2 3.4 0.6 88 91 90 -4.0 1.4 -1.3 11 1.0 23 0.0 1010 1018 1014 -3.3 1.7 Sunny intervals all day
17 0.1 5.1 2.6 72 92 82 -4.4 2.9 -0.8 22 3.6 87 1.1 1009 1016 1012 -4.2 7.2 Sunny all day
18 -0.7 1.2 0.3 70 80 75 -5.2 -3.3 -4.3 31 9.1 220 0.0 1015 1019 1017 -10.3 6.6 Sunny intervals all day
19 -7.2 2.7 -2.3 78 89 84 -9.4 -1.1 -5.3 10 0.7 17 0.0 1007 1019 1013 -8.3 6.1 Sunny intervals all day
20 -4.1 3.7 -0.2 74 91 83 -6.1 0.0 -3.1 13 1.3 34 4.1 1000 1007 1004 -9.2 6.8 Sunny intervals all day
21 -5.5 1.4 -2.1 84 89 87 -7.7 -0.8 -4.3 11 0.5 13 0.4 985 1000 993 -9.1 0.0 Cloudy am, rain pm
22 -5.6 4.2 -0.7 88 92 90 -7.4 2.1 -2.7 10 0.2 5 0.0 985 990 988 -9.2 6.8 Sunny all day
23 -5.7 4.1 -0.8 89 92 91 -7.3 2.6 -2.4 12 0.7 18 7.0 986 991 989 -6.4 0.7 Rain am, showers pm
24 -1.4 4.2 1.4 91 93 92 -2.9 2.8 -0.1 7 0.3 7 2.0 985 988 987 -6.9 0.3 Brief sunny intervals all day
25 -0.4 6.2 2.9 91 93 92 -4.3 4.6 0.2 12 1.3 32 0.2 988 1002 995 -1.8 7.5 Sunny all day
26 2.8 8.5 5.7 86 92 89 0.9 6.5 3.7 21 3.2 76 2.6 999 1002 1000 -1.5 5.3 Sunny am, showers pm
27 2.9 7.3 5.1 71 89 80 -1.9 3.3 0.7 30 6.4 154 1.1 997 1006 1002 -5.4 6.5 Sunny intervals all day
28 -0.4 6.8 3.2 81 91 86 -3.0 3.5 0.3 16 3.0 71 0.7 998 1007 1003 0.8 5.5 Sunny intervals all day
29 3.6 5.3 4.5 86 91 89 1.8 3.0 2.4 25 5.4 131 10.9 989 998 993 2.4 0.0 Rain, intermittent all day
30 4.2 6.1 5.2 90 92 91 2.4 4.4 3.4 21 3.3 80 4.4 988 994 991 0.0 0.0 Drizzle am, cloudy pm
31 1.4 4.3 2.9 79 90 85 -1.6 2.3 0.4 28 7.7 186 0.0 994 1002 998 0.0 0.1 Sunny ints am, cloudy pm
0.8 6.8 3.8 83 91 87 -1.7 4.6 1.4 19 3.1 2322 73.2 1002 1010 1006 -3.5 98.7  

Graphs for December 2009
Figure 1. Temperature and Rainfall for December 2009.
Figure 2. Sunshine, air pressure and mean wind speed for December 2009.
Figure 3. Wind direction for December 2009.
Figure 4. Soil & sea surface temperature (SST) for Lyme Bay for December 2009.
Figure 5. Wind run, maximum gusts and mean pressure for December 2009.