Royston (Iceni) Weather Station
Daily Weather Observations - October 2001
October 2001 Weather Review
October 2001 was a month of excesses weatherwise in Royston; temperatures and rainfall were both considerably above average, whilst sunshine registered an increase on the average also, but by a more modest amount.
An exceptional rainfall event occurred on 21st October when in a little under 17 hours from 0405 GMT to 2040 GMT an amount of 86.9 millimetres rainfall was recorded. As this period extends over the end of the "rainfall day" (24 hours ending 0900 GMT) this total is registered against 2 days viz. 20th (51.8 millimetres) and 21st (35.1 millimetres).
The exceptional nature of this event is illustrated by the fact that such a rainfall in this area is estimated by the Meteorological Office to have a return period of 140 years. Even the total recorded for 20th only makes it the wettest day in Royston since 22nd September 1992 and the wettest October day since at least 1972 (from which daily records are readily available).
This heavy rainfall increased the total for the month to 137.8 millimetres, which is 242% of the 1971/2000 average. It was the wettest October in Royston since 1865, although the rainfall total was only 0.1 millimetre higher than in October last year! The number of "rain days" (0.2 millimetres or more) was 20, whilst on 15 of these days 1.0 millimetre or more was recorded.
Rainfall duration in the month was 72.4 hours, a relatively low value given the high monthly total but explained by the intensity of the rainfall on 21st (which, incidentally, was not accompanied by any thunder making it an even more noteworthy occurrence). Thunder was not heard on any other day in October.
Temperatures hit the headlines as well as the rainfall since it was an unusually warm October, being the warmest in Royston since at least 1972.
The daily maximum and minimum temperatures were both above their respective 25 Year means on virtually every day of the month. This exceptional warmth was due principally to low pressure anchored to the west of the British Isles drawing in warm air from the south and south-west for much of the month (in contrast to September when a similarly placed anticyclone had the opposite effect by bringing cool north-westerly winds over the country).
Surprisingly, October was a little warmer than September. The mean day maximum temperature over the whole month was 17.1°C, which is 2.8°C above the 25 Year (1973/1997) average for Royston. Night minimum temperatures showed an even greater positive anomaly, the mean night minimum temperature of 11.4°C being no less than 3.8°C above average.
The highest temperature of the month of 23.0°C on 13th was not particularly noteworthy, however, having been exceeded in October in 6 years out of the previous 29 years. The lowest temperature in October was 8.1°C on 29th, making this the highest October minimum temperature in the last 30 years.
The mean earth temperature at 30 cms depth as measured at 0900 GMT daily was 13.6°C. This, too, was the highest October mean earth temperature in the last 30 years. The earth temperature ranged from a high of 15.0°C on 15th to a low of 11.6°C on 29th.
Not only was October warmer than September it was sunnier, too (by 19 hours). Total sunshine in October was 131.2 hours, which is 121% of normal. The highest daily sunshine value was 8.7 hours, recorded on 3rd, 5th, and 30th. Only 1 day in the month, 21st, was completely sunless.
Wind directions as observed daily at 0900 GMT were dominated by those containing a southerly component, 29 days out of 31, in fact. A westerly wind was noted on the other 2 days. The daily analysis of these wind directions is as follows: NORTH 0 days, NE 0, E 0, SE 2, S 13, SW 14, W 2, NW 0, and CALM 0.
The mean wind speed in October was 5.9 mph. The maximum wind gust speed in the month was 48 mph on 7th. The highest daily (00/00 GMT) mean wind speed was 12.1 mph on 1st, whilst the lowest daily mean wind speed was 1.0 mph on 13th.
The mean MSL air pressure for October was 1011.0 mB, which is approximately 4 mB below average. The highest and lowest pressure readings in the month were 1034 mB on 31st and 987 mB on 7th respectively.
The mean relative humidity in October was 89.3%. The highest daily (00/00 GMT) mean relative humidity value was 99.6 on 21st and the lowest such daily mean value was 78.5% on 31st. The absolute lowest relative humidity value in October was 56% at 1255 GMT and 1410 GMT on 31st.
Richard Barker
Richard Barker
Met. Observer, Royston (Iceni) Weather Station
6th November 2001
Return to Daily Weather Observations - October 2001 header page