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DECEMBER 2009 daily and monthly summary

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DECEMBER 2009
January 2010

1st - 7th
1st, HP 1013 hPa S Norway, LP 974 hPa S of Iceland. 2nd, drizzle and light rain very early am followed by heavy and sometimes prolonged showers from midmorning. 3rd light rain just after midnight with light rain showers mid morning. 4th, light rain starting 20.00h. 5th, sunny morning, light intermittent rain from 17.00 to 23.00h from warm front. 6th, LP 953 hPa NW of Donegal, moderate/heavy showery rain from cold front from 04.00 to 10.00h. 7th, light rain pm.
8th - 14th
Becoming more settled though mainly cloudy, light rain and drizzle from evening of 8th overnight into 9th. LPs near greenland and W Atlantic, HP 1029 hPa Spain. 10th, light rain shower early am then sunny, HP 1032 hPa Wales, 1029 hPa French Alps. 11th, sunny periods. 12th, very light rain showers am, light rain and drizzle evening. 13th HP 1036 hPa N Scotland to 1034 hPa S Norway, intermittent light drizzle night and early pm. 14th, intermittent drizzle early am, sunny periods from mid morning.
15th - 23rd
15th, light snow pm giving a slight and patchy dusting, turning to sleet and rain by evening. 16th, LP 1002 hPa N of Netherlands, HP 1037 hPa from S of Iceland to C Norway. 17th LP moves SSW toward Starights of Dover, light snow showers pm, moderate snow late evening and night. 18th, heavy snowfall before dawn giving 10 - 12 cm snow cover. 19th, sunny with some haze. 20th, LP 979 hPa W of Shetland, LP 989 hPa southern North Sea, occlusion brings another snowfall of about 3 cm before sunrise - total snow cover still around 10cm. 21st, new December record minimum temperature which rises quckly with a slight thaw later as warm front crosses giving some sleet and light rain. Snow cover about 6cm where undisturbed but icy 2 - 3 cm and rather patchy elsewhere. 22nd, a sunny day - slight thaw continues, freezing fog after nightfall. 23rd, LP Northern UK and Ireland, freezing fog to start followed by sleet then rain later - temperature rose above freezing only after midday, sunny pm.
24th - 31st
24th, light rain after midnight followed by heavier showers, snow cover now very patchy and max depth of 2.5cm where completely undisturbed. 25th, LP 980 hPa N Germany, LP 978 hPa 20°W of Ireland. 26th, passage of trough and cold front am with moderate rain (what little remaining snow/ice gone), and intermittent rain through the day and evening. 27th, some light rain just after midnight followed by a dry, cloudy day. 29th, LP 978 hPa 50°N 10 °W - very dull, light rain at first from warm front after 06.00 then spells of light/moderate rain intermittently all day from occlusion lasting well into the night. 30th more intermittent outbreaks of rain, night and into the daytime, light to moderate, overcast and very dull again. 31st, a quiet day with a late rain shower at night.

DECEMBER 2009 MONTHLY SUMMARY
ACTUAL TEMPERATURE
 AVERAGE
 Daily Maximum
5.6
 ºC ( -2.1C )*
 Daily Minimum
1.6
 ºC ( -1.9C )*
 Daily Mean
3.72
 ºC  
 EXTREMES
 High Maximum
12.3
 ºC (   6th )
 Low Minimum
-7.4
 ºC ( 21st )
 Low Maximum
-0.2
 ºC ( 19th )
 High Minimum
9.9
 ºC (  6th )
 
   
 Days with max => 10 °C
4
   
 Days with max < 5 °C
13
   
 Days with air frost
11
   
 
PRECIPITATION
 Monthly Total
72.1
 mm ( 96% )*
 Days with measurable precip
25
 Days ( +10 )*
   ...of which, days with >= 1.0 mm
13
 Days ( +2 )*
   ...and days with snowfall observed
5
 Days  
 Days with Snow Cover
5
 Days  
 Days with Thunder
0
 Days  
 RAIN RATE & EXTREMES
 High Rain Rate
20.8
 mm/hr (  2nd )
 High Rain Total in 1 day
14.0
 mm ( 29th )
 High Rain Total in 1 hour
2.8
 mm ( 6th, 10.00h)
 EVAPO-TRANSPIRATION
 Total for month
10.3
 mm  
 High Total for 1 day
1.0
 mm ( 6th )
APPARENT TEMPERATURE
 Low Wind Chill
-7.4
 ºC ( 21st )
 DAVIS HEAT INDICES THW & THSW
 Low Temp/Hum/Wind Index
-7.5
 ºC ( 21st )
 High Temp/Hum/Wind Index
12.0
 ºC (   9th )
 High Temp/Hum/Sun/Wind Index
13.1
 ºC (   9th )
 
DEWPOINT & HUMIDITY
 High Dewpoint
10.2
 ºC (   6th )
 Low Dewpoint
-9.6
 ºC ( 21st )
 Average Dewpoint at 14h
2.0
 ºC  
 Low Relative Humidity
62
 % ( 12th )
 Average RH at 14h
81
 %  
WIND SPEED & DIRECTION
 Monthly Average
1.60
 mph  
 Windiest day (Average)
5.5
 mph ( 6th )
 Highest Gust
29
 mph ( 6th )
 Dominant Direction
SW
 ( 28% )
 
BAROMETER
 Monthly Mean
1012.3
 hPa  
 High Barometer
1031.9
 hPa ( 11th )
 Low Barometer
981.4
 hPa ( 22nd )
SUNSHINE
 Max Sensor Exposure to direct sun
2.0
 hours/day (8 - 9 possible)
 Calculated Monthly Sunshine Hours
18.8
 hours  
 Estimated Actual Hours (approx)
58.0
 hours  
 Sunniest Day Measured
2.0
 hours ( 28th )
 Days with no sunshine
9
 Days  
 
FOG
 Number of Days with Fog
2
 Days  
NEW SITE RECORDS SET THIS MONTH
  • Lowest minimum temperature for December ( prev. -7.1 °C, 2000)
‡ SUN: Sunshine hours are calculated approximately and solely from solar radiation readings, but note that the solar sensor's exposure to sunshine in Midwinter is very limited. The sensor receives only up to 25% of total possible sunshine exposure this month due to obstruction. There is no allowance for sunshine by visual observation only, so the sunniest day figures above can be very significantly less than the actual daily sunshine duration.
THW = Shaded Heat Index calculated with cooling/warming effect of wind and humidity to give an apparent temperature.
THSW = Unshaded Heat Index calculated with cooling/warming effect of wind, humidity and full direct sunshine to give an apparent temperature.
EVAPO-TRANSPIRATION is drying effect due to sun and wind, and is equivalent to "negative rainfall"


   DAILY STATS DECEMBER 2009
 
TEMPERATURE ºc
HUMIDITY
SUN ‡
PRESSURE
RAINFALL
WIND SPEED
DIRECTION
 WEATHER
 NOTES
DATE
Low
(21-09h)
High
(09-21h)
Temp at 14.00z
RH %
at 14.00z
Dewpoint ºc
at 14.00z
Bright
sun hrs
hPa   †
at 14.00z
Day Total
(mm)
Average
(mph)
Max Gust
(mph)
Dominant
(Compass)
 Precipitation
 type etc ‡
                       
1st
0.3 5.5 5.4 78 1.9 0.2 1010.5 F 0.0 0.9 14 SSW  Sunny am
2nd
2.9 9.9 9.3 88 7.4 0.2 996.2 F 10.7 1.1 18 SE  SHRA++
3rd
7.1 7.6 5.4 80 2.2 0.0 997.5 R 1.5 1.8 16 SSW  Rain am
4th
1.8 6.9 6.3 70 1.2 0.5 1007.4 FS 1.0 1.4 14 WNW  Rain night
5th
5.2 11.3 10.1 77 6.3 0.1 1000.5 RS 5.3 4.0 19 SW  Rain eve
6th
9.9 12.3 10.4 64 3.9 1.5 997.6 RQ 7.1 5.5 29 SSW  Rain am
7th
8.1 10.6 10.1 78 6.4 0.0 997.2 F 3.3 3.9 25 SW  Rain pm
8th
4.9 9.3 9.2 73 4.6 0.1 1012.1 RS 0.8 2.3 19 SSW  Rain eve
9th
8.5 12.0 11.9 88 10.0 0.1 1018.1 RS 0.5 1.1 14 SSW  Rain night
10th
6.4 9.4 9.4 69 4.0 1.2 1027.8 RS 0.3 1.3 16 SSW  SHRA am, Sunny
11th
1.3 6.6 6.5 88 4.7 1.2 1030.9 ST 0.0 0.4 10 N  Sunny periods
12th
4.4 7.8 7.5 62 0.7 1.3 1029.2 FS 0.8 1.5 13 N  SHRA
13th
3.7 5.0 4.8 85 2.5 0.0 1024.6 F 0.5 1.0 13 N  Rain am/eve
14th
1.7 5.3 5.2 74 0.9 1.3 1020.1 FS 0.5 0.1 8 N  Drizzle am
15th
-3.6 0.1 0.1 90 -1.3 0.8 1017.7 FS 0.0 0.0 3 SE  Haze
16th
-6.1 1.0 0.2 86 -1.9 0.1 1009.3 F 1.5 0.2 6 SSW  Snow pm
17th
0.6 3.7 3.7 69 -1.5 1.0 1006.9 ST 0.5 4.7 25 N  SHSN pm/Snow eve
18th
-1.7 0.3 0.2 87 -1.9 0.8 1013.2 ST 0.8 1.4 12 N  Heavy snow am
19th
-3.1 -0.2 -0.7 81 -3.6 1.3 1009.5 F 0.0 1.4 13 N  Sunny
20th
-2.4 0.3 -0.3 73 -4.6 1.5 997.5 FS 0.5 0.7 11 SW  Snow am
21st
-7.4 1.9 1.1 90 -0.3 0.0 988.3 F 1.3 0.0 5 WNW  Sleet/Rain pm
22nd
-0.2 2.2 1.4 90 -0.1 1.5 986.9 RS 0.3 0.3 10 SSW  Rain am, sunny pm
23rd
-5.1 4.2 2.4 92 1.3 1.8 989.8 FS 1.8 0.6 14 SE  Rain am
24th
1.8 5.1 4.5 91 3.2 0.0 986.2 F 3.8 0.4 14 SE  Rain am
25th
2.0 3.1 3.0 86 0.9 0.2 1000.3 R 0.0 1.5 14 WNW  Cloudy
26th
-0.3 7.9 7.6 86 5.4 0.0 999.7 FS 9.1 4.5 19 SW  Rain
27th
5.1 7.1 6.4 69 1.1 0.2 997.7 R 0.3 4.0 20 SW  Rain am
28th
-1.5 4.7 4.2 84 1.7 2.0 1002.7 F 0.0 0.2 7 SW  Sunny spells
29th
-0.3 3.8 3.7 91 2.4 0.0 990.7 F 14.0 0.3 10 SE  Rain
30th
3.8 5.3 5.1 93 4.0 0.0 990.3 RS 5.6 0.5 6 NW  Rain
31st
3.1 3.7 3.6 82 0.8 0.0 997.0 ST 0.3 2.6 17 N  Shower night
                         
‡ SUN: Sunshine hours are calculated approximately and solely from solar radiation readings, but note that the solar sensor's exposure to sunshine in midwinter is very limited. The sensor receives less than 25% of total possible sunshine exposure this month - none in the morning - and there is no allowance for sunshine by visual observation only, so the figures above can be very significantly less than the actual daily sunshine duration.
† Barometer trend (previous 3 hours) : F = falling, ST = steady, R = rising; Q = quickly, S = slowly
Weather Notes use METAR codes: SHRA = rain showers; SHSN = snow showers; SN = snow; RASN = Rain and snow; '+' = heavy;