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Today, Monday 16 March,¬†was the UK’s warmest day of the year so far — as long as you count observations made at the London Weather Centre, where the temperature reached 17.2 Celsius today. If you are one of those who doubt the integrity of the exposure of this site, then the warmest is still the 16.9 C recorded in Canterbury on February 27.

One might¬†call this warm-ish and sunny weather ‘spring-like’ but as it is already spring, meteorologically, then so it should be. It is one thing to talk about ‘spring-like’ when it is still winter but another, almost tautological, matter to do so when spring has sprung. Unless one holds on to the notion that spring begins around March 21.

Semantics aside, though, we have high pressure near or over the UK to thank for what meteorologists are pleased to call this ‘settled’ spell. The centre of this anticyclone looks like shifting northeastwards into Scandinavia towards the weekend; its influence should ensure a continuation of the dry weather in many areas but it will encourage winds from a colder northeast or easterly direction.

High pressure then, if the models are correct, regresses into the Atlantic by the start of next week, Monday 23 March. This will give us a north to north-westerly flow that will be neither warm nor particularly cold. It will keep many parts of the country dry, though, and it seems likely that some areas will enter an ‘absolute drought’, the definition of which is a period of 15 days or more when no measurable rainfall is recorded (less than 0.2 mm per 24 hour period).

droughtIt’s a slightly archaic expression, adopted by G J Symons in 1887 in his work British Rainfall. It dropped out of official favour around 1960 as more sophisticated hydrological and statistical measures were introduced. A ‘dry spell’, added to weather glossaries in 1919, is a period of 15 consecutive days when no more than 1.0 mm of rain falls in a single day.

Confusingly, perhaps, there is – or was – also a ‘partial drought’: a period of at least 29 consecutive days, whose mean daily precipitation does not exceed 0.2 mm.

Are these definitions useful? Possibly not; but perhaps they should be borne in mind when casual bandying phrases such as ‘dry spell’, lest these be confused — unlikely though that may be — with these withered turns of phrase.