Spring is in the air
A fine and dry week is expected with high pressure dominating our weather, but forecasting temperature levels will be challenging to say the least.
Firstly, air is flowing over the Pennines from west to east, drying and warming as it does so.
This is called the Fohn effect, resulting in temperatures in the Vale of York, for example, in double figures.
Yesterday 12C (54F) was recorded in Durham, with a definite feel of spring in the air.
The second complication is a lowering temperature inversion.
Counter-intuitively this results in temperatures at the top of a hill or mountain being higher than those in the valley bottom, if the inversion is low enough.
This is because with high pressure, the air gradually descends, and warms as it does so, hitting the top of the hill first.
A low inversion also means that any cloud in western areas cannot get over topographic barriers like the Pennines, leaving clear blue skies to the east of high ground.
The computer is often poor in modelling such situations, overstating amounts of cloud and as a consequence being far too pessimistic with temperature levels.
Later this week as air pressure falls, the inversion will rise, with generally cloudier conditions likely – in theory at least!
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