COLUMN: Weather Wise with Gordon Currie

A shrub and berries covered with a heavy hoar frost. (GL 6806)
A shrub and berries covered with a heavy hoar frost. (GL 6806)
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Gordon reflects on yet another colder than average winter:

A simple, saner lesson may he learn

Who reads thy gradual progress, Holy Spring;

Thy leaves possess the season in their turn,

And in their time thy warblers rise on wing.

How surely glidest thou from March to May . . . .

Thy warmths from bud to bud

Accomplish that blind model in the seed,

And men have hopes, which race the restless blood,

That after many changes may succeed

Life, which is Life indeed.

There’s a curious but very realistic symbolism in Tennyson’s glorious theme which portrays The Progress of Spring, inspired by the scenery of his favourite Tennyson Down in the Isle of Wight, one place in the British Isles which frequently experiences the earliest arrivals of the season.

Even though our region is much further north, one could sense a definite similarity of Tennyson’s inspiration on the last day of February. Cloaked in a sunrise scene of white hoar frost and a temperature of 23F (-5C) the picture changed swiftly within two hours as sunlight gained mastery over hoar frost which seemed to shrink as if broken or defeated into the refuge of the hedgerow shadows.

The sun’s warmth “from bud to bud” was already taking effect, transforming sparkling needles of hoar frost into life-giving beads of moisture which, in places, were almost steaming. The magnitude of change, signifying the final chase between one season and the next, seemed to be upon us.

For the purpose of meteorological statistics the winter season ends on the last day of February and, more often than not, with some form of flourish. It is interesting to recall the events of one year ago when the British Isles was flooded with a sub-tropical south-westerly flow.

On the penultimate day, the 28th, the Met Office released a much trumpeted pronouncement to the effect that Aberdeen’s February temperature record of 64.2F (17.9C) established in 1898 would quite possibly be broken (noted, global warming advocates gearing up for full hue-and-cry!). As things turned out, it wasn’t – the day’s maximum only managed 63.1F (17.2 C).

This year’s winter season, December 1 to February 28, has ended with a mean temperature figure of 38.0F (3.3C), 1.0 F (0.6 C) below the long-term average.

Since the winter of 2007-08 there has been a marked decline in the winter temperature trends, with four out of the past five winters being colder than normal, the coldest being 2009-10, having a mean of 33.0F (0.5 C). Last year’s mean was fractionally above normal, 39.5F (4.1 C).

This cooling trend certainly becomes more emphasised when you realise we’ve left behind those mild winters of 2006-07, 41.2F (5.1 C) and 2004-05, 41.1F (5C).

This year’s sub-normality was not helped by the lengthy cold spells of December and January coupled with the depressing grey skies of February with the month’s mean temperature being 37.1F (2.8C) against the average figure of 39.0F (4C).

One of the principal features of temperatures over the winter has been the coldness of the days, rather than anything exceptional with the overnight minima. Looking at the number of mild winter days with readings of 50F (10C) or higher since the start of the new century, we begin with only eight days in this category for the season just ended. In 2000-01, 14 mild days occurred, mainly in December 2000 (ten ). The winter of 2001-02 managed 24 mild days, having a remarkable run of 16 consecutive days between January 27 to February 12. The winter of 2003-04 had 25 mild days, peaking with 61F (16C) on February 3.

This began a group of five winters notable for daytime mildness between 2003 and 2007, the mildest of all being 2006-07 having 31 days with maxima well above the classification, peaking at 57F (14C) on December 14. This particular season was the warmest winter since the record breaker of 1997-98.

With a total winter rainfall figure for the three months of 216mm (8.64in) the most redeeming feature of the season has been a steady decrease in rainfall figures since one of our wettest Decembers, 127.7mm (5.10in), followed by 60.3mm (2.41in) in January, decreasing to 28mm (1.12in) for February, which happens to be 17mm (0.68in) below the long period average, constituting the first drier-than-normal month for almost a year.

One could suppose that this season’s winter rainfall figure stands in more favourable light compared with some of our wettest winters, such as 2006-07 having 263.7mm (10.54in), but that high figure came in the wake of a very hot, dry summer. There is much scope for improvement!

With regard to February, drier than average months are usually caused by the seas around the British Isles being at their coldest and the corresponding air masses which flow over them being themselves colder and therefore unable to pick up so much moisture.

Mercifully the scientific theory of the seas versus atmosphere relationship managed to make a timely effect on February’s weather, even though the greater part of the month was influenced by cold, continental air streams.

These are usually very dry, but unfortunately when a thin layer of moist air becomes virtually trapped in the middle levels of the atmosphere, the circumstances then produce a persistent, amorphous layer of stratocumulus cloud in February which remind us either of the bitter Russian Steppes, or the legendary Swedish steel nights – known for their cutting severity!

PROSPECTS FOR THE WEEK AHEAD

More unsettled conditions are expected to become established by the end of this week, as low pressure systems manage to push across the British Isles from the south-west, possibly bringing warmer air-streams from the south-eastern parts of Europe. This should ensure a significant rise of temperatures, accompanied by some rain at times. However, a careful watch must be observed on the behaviour of a very strong high over Greenland at the present time. Developments over the far northern Atlantic are very uncertain at the time of writing but a southward push of this high pressure system could possibly introduce much colder weather later in the week.

Intervals of sunshine and showers, or longer spells of rain accompanied by higher temperature levels, 50 -55F (10 -13C), will make it feel more spring-like this coming week, but beware of a sudden change to colder, northerly winds, wintry showers and frosts late in the week.