The Iberian Thermal LowAdded : Thursday at 14:45 Right, first of all, the Iberian Thermal Low is nothing new. It's not a phenomena or some new spangled phrase in meteorology as many of us know...
If you take a look at the pressure chart for today you can see the Iberian Thermal Low over... well, Iberia (Spain/Portugal) :-
This is basically a shallow surface low pressure system which is devoid of any frontal systems and is caused by intense heating in the centre of Spain during the Summer months.
What basically happens, is that the surface air is heated which expands (as hot air does) and this expansion displaces the cooler air above Spain and as a result the air pressure falls. This is a feature of many dry, arid land masses in the Summer months and also happens in places such as the Tibetan Plateau :-
These thermal lows can reduce air pressure during the day by anything up to 5-10mb, although 3-5mb is more common.
Usually, they are what we call seasonal diurnal features. This means that they are there during the Summer months and are more intense by day before filling during the evening and overnight.
Because they tend to occur in arid and dry areas, they rarely form showers or thunderstorms due to the lack of available moisture at the surface.
With the Iberian Thermal Low though, sometimes the Atlantic jet stream taps into it and sends it on its merry way North. These are the features which then develop a frontal system and approach the UK from the South.
On Friday and Saturday, the GFS ► is progging this happening, albeit in a rather messy and clumsy way.
Here is the jet stream forecast for Saturday :-
You can see a branch of the jet stream running across Spain and heading North towards the UK. This means that features underneath are then picked up and head in the same way too.
By Sunday, the GFS ► brings the low pressure North and by this point it's become mid latitude and has developed a warm/cold front on it :-
Much of the forcing in this system stays a little too far to the West to be considered what we would call a classic Spanish plume scenario, but it shows you the physics in action and how these thermal lows develop, interact with the jet stream and end up approaching the UK from the South.
Cool eh? Well, more muggy, warm... But you know what we mean...
METEOROLOGIST : MARSH |