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| Casement Aerodrome 1961-1990 averages | | | | | | | | | | | | | |
| TEMPERATURE (degrees Celsius) | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| mean daily max. | 7.8 | 7.6 | 9.6 | 11.8 | 14.6 | 17.7 | 19.7 | 19.3 | 16.8 | 13.6 | 9.9 | 8.3 | 13.1 |
| mean daily min. | 2.0 | 1.7 | 2.5 | 3.2 | 5.7 | 8.6 | 10.7 | 10.3 | 8.5 | 6.7 | 3.6 | 2.8 | 5.5 |
| mean | 4.9 | 4.6 | 6.0 | 7.5 | 10.1 | 13.1 | 15.2 | 14.8 | 12.6 | 10.1 | 6.7 | 5.6 | 9.3 |
| absolute max. | 15.4 | 14.7 | 18.8 | 21.3 | 24.7 | 27.5 | 29.8 | 30.5 | 24.7 | 21.3 | 17.7 | 15.4 | 30.5 |
| absolute min. | -12.4 | -10.3 | -7.8 | -4.5 | -3.0 | 0.3 | 2.5 | 2.5 | -0.3 | -4.1 | -6.2 | -9.7 | -12.4 |
| mean no. of days with air frost | 7.5 | 7.7 | 6.3 | 4.9 | 1.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.4 | 5.9 | 6.6 | 41.3 |
| mean no. of days with ground frost | 15.3 | 15.0 | 13.1 | 12.8 | 6.3 | 1.1 | 0.1 | 0.1 | 1.6 | 4.5 | 11.0 | 13.5 | 94.3 |
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| RELATIVE HUMIDITY (%) | | | | | | | | | | | | | |
| mean at 0900UTC | 87 | 86 | 84 | 80 | 77 | 77 | 79 | 81 | 84 | 86 | 87 | 87 | 83 |
| mean at 1500UTC | 82 | 77 | 72 | 68 | 68 | 68 | 68 | 68 | 71 | 76 | 81 | 83 | 74 |
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| SUNSHINE (hours) | | | | | | | | | | | | | |
| mean daily duration | 1.63 | 2.38 | 3.04 | 4.85 | 5.65 | 5.63 | 5.01 | 4.83 | 4.04 | 3.07 | 2.16 | 1.42 | 3.64 |
| greatest daily duration | 8.1 | 9.2 | 10.9 | 13.6 | 15.4 | 16.0 | 15.4 | 14.4 | 12.3 | 9.8 | 8.5 | 6.9 | 16.0 |
| mean no. of days with no sun | 10 | 7 | 5 | 2 | 2 | 2 | 1 | 2 | 3 | 5 | 7 | 11 | 55 |
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| RAINFALL (mm) | | | | | | | | | | | | | |
| mean monthly total | 68.7 | 50.7 | 53.8 | 49.9 | 56.6 | 53.0 | 48.9 | 63.7 | 58.7 | 67.2 | 67.2 | 73.1 | 711.4 |
| greatest daily total | 31.4 | 42.8 | 30.0 | 35.3 | 34.3 | 108.6 | 41.4 | 73.0 | 32.1 | 48.5 | 58.4 | 42.9 | 108.6 |
| mean no. of days with >= 0.2mm | 18 | 14 | 17 | 14 | 15 | 14 | 14 | 14 | 15 | 16 | 16 | 17 | 185 |
| mean no. of days with >= 1.0mm | 13 | 10 | 12 | 10 | 11 | 10 | 9 | 10 | 10 | 11 | 11 | 12 | 131 |
| mean no. of days with >= 5.0mm | 5 | 3 | 3 | 3 | 4 | 3 | 3 | 4 | 4 | 4 | 4 | 5 | 45 |
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| WIND (knots) | | | | | | | | | | | | | |
| mean monthly speed | 14.1 | 12.5 | 12.8 | 10.1 | 9.1 | 8.7 | 8.9 | 8.7 | 10.1 | 11.2 | 12.3 | 13.3 | 11.0 |
| max. gust | 80 | 78 | 71 | 59 | 63 | 53 | 58 | 58 | 69 | 65 | 68 | 81 | 81 |
| max. mean 10-minute speed | 57 | 54 | 47 | 43 | 43 | 36 | 39 | 39 | 46 | 44 | 49 | 57 | 57 |
| mean no. of days with gales | 5.2 | 2.7 | 2.7 | 0.6 | 0.5 | 0.1 | 0.1 | 0.2 | 0.6 | 1.4 | 2.4 | 3.7 | 20.3 |
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| WEATHER (mean no. of days with...) | | | | | | | | | | | | | |
| snow or sleet | 4.6 | 4.8 | 3.5 | 1.4 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.4 | 2.1 | 16.9 |
| snow lying at 0900UTC | 2.4 | 1.8 | 0.4 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.5 | 5.3 |
| hail | 0.8 | 1.2 | 2.8 | 2.2 | 1.3 | 0.5 | 0.1 | 0.1 | 0.3 | 0.1 | 0.7 | 0.6 | 10.7 |
| thunder | 0.0 | 0.1 | 0.2 | 0.3 | 0.9 | 0.9 | 0.8 | 0.6 | 0.3 | 0.2 | 0.2 | 0.1 | 4.8 |
| fog | 2.5 | 2.3 | 1.8 | 2.4 | 1.6 | 1.4 | 1.2 | 2.8 | 2.9 | 2.7 | 1.8 | 2.3 | 25.9 |