Lows Within Lows Within...Added : Tuesday at 13:27 Right, we have the weather sort of sussed over the next week or so, so let's take a look at a synoptic chart and see what tickles our fancy...
This is the chart we are going to decode :-
Looks like a rather typical Winter chart which would expect to see at our latitudes around the end of November, but our attention is really on lows ONE and TWO. Notice how close they are to each other and also how low ONE is actually embedded within low TWOs circulation.
How can this happen? Well, to be honest it's not that uncommon. The reason is simply due to temperature differences created within low ONE. If we take a look at the upper air temperatures for a few hours before you'll see what we mean :-
You can see that low TWO has sent some cooler air South but warmer air in low ONE contrasts with this and a frontal system is formed. At this point we have decent temperature contrasts either side of low ONE and as a result it develops and heads North. The other thing is the position of the jet stream. If we have a look at the jet stream for the same time :-
Ta-da! You can see that the jet stream is much further South than low TWO and as a result it sort of stagnates where it is (in an upper level low). The jet stream then picks up low ONE and sends it Northeast and with the addition of temperature contrasts this develops into half decent weather system.
So, in fact, when you see these two lows interacting with each other then you'll find that the primary low (low TWO in this case) is stagnating and that all the energy is focused on low ONE which has the temperature contrasts and jet stream interaction.
What's always worth watching is how the secondary low (low ONE) interacts with the primary low (low TWO) which we call dumb-belling as they interact with each others circulation. Sometimes they can deviate the course of the primary low or deepen it markedly thanks to changing what we call the "centre of gravity" of the system.
For those of you wondering how the Buys Ballot Law works in scenarios like this (i.e If you stand with your back to the wind then high pressure is on the right and low pressure is on the left in the Northern Hemisphere) then it doesn't. But it means that if you stand with your back to the wind in dumb-belling lows like this then the lowest pressure of the systems will always be on your left... sometimes.
METEOROLOGIST : MARSH |