All About The Fizzle..Added : Thursday at 14:30 We've all been there, watching the radar images as an impressive thunderstorms the size of a mothership heads off the North French coast and into the Channel. You are convinced that once the storm reaches the UK then boom! crash! Off the mothership goes again, but instead....
Thunderstorm forecasting is a hidden art. Most meteorologists know when the ingredients are there for certain storms, we can tell whether they are likely to be scattered or cluster into more organised systems based on the atmosphere, but the questions of where, when and if are ones which are usually only answered the day after once profiles are available.
If you take a look at AROME for this afternoon then you can see it forecasts a thunderstorm to develop across Exmoor :-
Decent agreement with this, after all, we have cooler air coming in from the West at height, a surface low moving North and a combination of the air being forced up (orographic lift) and sea breezes means that this is indeed a pretty ripe spot.
Later in the afternoon and you can see AROME taking the storm towards South Wales with further storms developing near Exmoor. This bit is important, the thunderstorms need moist, warm air flowing in near the surface, cut that off and the storms decay quickly.
This can happen because of two reasons, the first is that the upper level winds are too strong, this effectively rips the top and bottom of the storm apart and cuts of the vertical flow of the storm, the other is moving over colder water.
AROME knows the temperatures of the Bristol Channel and hence cuts off the moist supply :-
The same effect can be seen sometimes when seeing storms leave Northern France and fizzle out in the Channel. The reasons can be any one/or all of the following :-
- Cool surface sea temperatures
- Strong vertical shear which cuts off the supply near the surface
- Subsiding air off the coast due to the sea breeze effect
- Nature couldn't be bothered..
OK, the last one we made up, but when thunderstorms are forecast then meteorologists look at where and why they might develop, but at the back of our little minds, we are also factoring in the fizzle effect and whether this may come into play too.
At the end of the day though, nature holds the cards...
METEOROLOGIST : MARSH |