COLUMN: Weather Wise with Gordon Currie

Heavy rain in October affected the region's roads.
Heavy rain in October affected the region's roads.

Gordon takes a look at the wettest October for nine years.

Reviewing the weather conditions of October this year, one is prompted never to underestimate the interactions of so many conflicting air-masses which have ever widening margins of temperature contrasts, as the polar regions are cooling rapidly, while the sub-tropical latitudes of the North Atlantic and Mediterranean regions retain an element of summer heat.

Last month, the volatility of the atmosphere over the British Isles increased progressively as the month wore on, culminating in the fully fledged tornado which struck the locality of Huby village in the Vale of York, south-west of Easingwold on the evening of October 25th.

The persistence of southerly winds with spells of warm, humid air characterised the month’s weather, resulting in a notably mild month with mean temperature of 54.6 F. (12 C.) making it the warmest October since 2006 and 
2007, 55.0 F. (13 C.) in both months.

These figures compare with last year’s cold October, with a mean figure of 46.6 F. (8.1 C.) which was the coldest October since 1993.

One noteworthy feature this year was the mildness of the nights, without a single air frost being recorded.

The mean minimum temperature was 48.8 F. (9 C.), compared with 40,6 F. (5 C.) last year. Needless to say, these figures give some clues towards the prolificacy of the autumn sown crops which have been such a welcome feature this year.

Total rainfall for October was 107.5 millimetres (4.30 inches) compared with the long term average of 62 mm. (2.5 ins).

However, in spite of this high figure, the cumulative total rainfall for the year up till October 31 is 505.3 mm. (20.21 ins) compared with 837.7 mm. (33.50 ins) for the same period last year.

This means that provided we experience normal rainfall figures for November and December, we should end up with a near-normal 12 month total and a much drier year than 2012.

This October has been the wettest since 2004, when 124.8 mm. (4.98 ins) was recorded. For the record, 139 mm. (5.56 ins) was registered in October 2000, the highest figure since October 1960.

Taking a look at the general run of weather last month, the first ten days tended to be dominated by southerly winds bringing warmth from southern Europe.

Maximum temperatures peaked at 73 F. (22 C.) on the 4th in a shaft of sunlight, just ahead of a cold front which deposited 12 mm. rainfall (0.50 ins).

Following another reading of 70 F. (21 C.) on the 7th, the pressure pattern changed temporarily, as a depression developed in the southern North Sea on 13th-14th, creating a much cooler, moist north-easterly air-flow on its northern side.

This caused a few days of dull, gloomy weather with low cloud sweeping in off the North Sea and maxima of only 52 F. (11 C.) on the 14th and 15th.

Eventually, this somewhat static situation was swept away by a vigorous in-coming Atlantic front, giving strengthening winds and large falls of pressure, coupled with 10 mm (0.40 ins) rainfall.

A very marked clearance followed this trough, with very clear Atlantic air which gave us a brilliantly sunny day on the 17th, traditional it would seem to the legendary “Saint Luke’s Little Summer” (St. Luke’s Day, 18th).

By the 18th however, a very large and deep Atlantic depression slowed its eastward movement down and became almost stationary to the south-west of the British Isles for several days until the 26th.

The benefit of this situation of course became the re-establishment of warm, southerly winds again, bringing bands of quite thundery rainfall from France northwards across the country.

It was interesting to observe how, because of the lateness of the season and weakening sunlight, the cumulonimbus shower clouds did not reach their precipitating stages until an hour or two before sunset.

Nevertheless, the origins of some Continental warmth in the lower atmosphere sparked great low-level instability near the ground, especially on the early evening of the 25th, when thunderstorms and a devastating tornado were reported around Huby and Easingwold.

The proximity of the rising shoulders of land towards the North Yorkshire Moors may have contributed towards the increased instability of the air-mass, coupled with obstructing the forward eastward movement of the entire cloud structure.

PROSPECTS FOR THE WEEK AHEAD

By the end of this current week, our weather pattern is expected to have been restored to the North Atlantic Westerly type again, with low pressure systems to the west and north-west of Scotland, with milder south-westerlies flowing across the country. However, it seems likely that much colder air will stand its ground to the north of Scotland, making the passage of fronts somewhat difficult at times across Scotland. In these circumstances, it would appear that the establishment of westerlies by the end of this week, may not have the confidence to last for a lengthy period, a point to watch!

Mainly unsettled and changeable with further rain at times. Alternating sunny spells at times. Becoming milder generally, 50 – 55 F. (10 – 13 C.), but possibly turning colder after a few days, with some wintry showers later in the week, and night frosts.