Royston (Iceni) Weather Station

Daily Weather Observations - May 2006

It was a warmer and wetter May than average, but also rather dull.

Temperatures (particularly day maximum temperatures) tended to go against the normal trend for May by going down through the month rather than up! The highest day maximum temperature (26.0°C) of the month was reached as early as 4^th whilst the lowest day maximum temperature (13.2°C) occurred as late as 29^th.

During the following night (29^th/30^th) both the lowest minimum and lowest grass minimum temperatures of the month were recorded. These were 3.2°C and 1.7°C respectively. The highest night minimum temperature in May was 13.0°C on 26^th/27^th.

The mean daily maximum temperature in May was 17.6°C, which is 0.6°C above the 30 Year (1976/2005) average. The mean night minimum temperature was 1.6°C above average at 9.0°C. Despite the cold end to the month it was still the warmest May in Royston since 1999.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 14.5°C, peaking at 16.1°C on 13^th and falling to its lowest value of 12.0°C on 2^nd.

After a consecutive run of 6 drier than average months (November 2005/April 2006) the May rainfall ended the sequence with a total one and a half times the normal. This was mainly due to a wet second half of the month as the first half had been fairly dry.

Total rainfall in May was 70.2 millimetres, which is 149% of the 30 Year (1971/2000) average. The number of "rain days" (0.2 millimetres or more) was 19, whilst on 12 of these days rainfall exceeded 1.0 millimetre. The wettest day of the month was, surprisingly, in the drier first half of the month with 9.2 millimetres rainfall on 6^th. Rainfall for the period 1^st/16^th was 18.5 millimetres, but this was followed by 51.7 millimetres rainfall from 17^th/31^st. It was the wettest May in Royston since 2000. Rainfall duration in May was 67.1 hours.

Thunder was heard on 2 days (12^th & 24^th) in May, and hail was observed to fall on 1 day (29^th).

Despite 7 days in May experiencing over 10 hours sunshine the month still ended with a sunshine deficit compared to the 30 Year (1971/2000) average. Total sunshine in the month was 158.3 hours, which is 83% of normal.

The sunniest day in May was 11^th with 14.0 hours sunshine. At least some sunshine was recorded on every day of the month, even though this was only 2 minutes on 6^th and 4 minutes on 8^th.

The first half of May was fairly calm but the second half of the month saw a fourfold increase in the mean wind speed! In figures the mean wind speed for 1^st/16^th was 1.1 mph, but this increased to 4.3 mph for 17^th/31^st. Some notably windy days (for time of year) occurred in this latter period with daily maximum gust speeds exceeding 30 mph on 9 days. The maximum gust speed recorded in May was 44 mph on 19^th.

The highest daily (00/00 GMT) mean wind speed in May was 10.6 mph on 19^th, whilst the lowest daily mean wind speed was 0.0 mph (to nearest 1 decimal place) on 7^th. The mean wind speed over the whole month was 2.7 mph.

The analysis of wind directions as observed at 0900 GMT daily was NORTH 2 days, NE 2, E 0, SE 3, S 4, SW 9, W 6, NW 4 and CALM 1.

The mean MSL air pressure in May was 1011.4 mB, which is 5 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values in the month were 1027 mB and 984 mB on 31^st and 22^nd respectively.

The mean relative humidity in May was 81.5%, ranging from a highest daily (00/00 GMT) mean value of 94.5% on 8^th to a lowest daily mean value of 63.7% on 12^th.

The absolute lowest relative humidity reading in May was 28% at 1350 GMT on 12^th.

Fog (visibility < 1000 metres @ 0900 GMT) was observed on just 1 day (9^th) in May.

With May being the last month of Spring in meteorological terms a few summary details for Spring 2006 (March/May) are given. The mean daily maximum temperature in Spring was 13.4°C, which is 0.1°C below the 30 Year (1976/2005) average. The mean night minimum temperature in Spring was 0.3°C above average at 5.4°C. Total rainfall in Spring was 136.2 millimetres, which is 102% of the 30 Year (1971/2000) average, whilst Spring sunshine of 411.7 hours was 93% of the 1971/2000 normal.

Met. Observer, Royston (Iceni) Weather Station

6^th June 2006

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