St Jude’s Storm Approaches

Brace yourselves, Britain: a storm is on its way!

You may have heard about it already. You may be thinking this is a bit much for one week, what with the storm that hit London on the night of the new Thor movie premiere last Tuesday, and what with the torrential rain bands that have swept across these past few days, but we haven’t seen the end of it yet.

If you haven’t check the Met Office and the BBC, who are currently producing the best reports on the event, you should do. There’s some great maps and graphs which show the expected route and rainfall concentrations, and wind speed. The storm is in the process of passing over as I write this, but is due to hit with fullest force on Monday.

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The South of England is said to be the most severely affected, with greatest wind speeds of more than 70 miles per hour. The actual eye of the storm is most likely to pass over Wales and the Midlands, and the whole of the UK is probably going to experience bad weather in general, but currently the strongest estimation of the storm’s course is that the South will suffer.

In an amazing display of coincidence, the storm is falling on St Jude’s Day. Now, St Jude is the patron saint of depression and lost things, so naturally the storm is names after this saint. It’s so poetically British. I love it. I just hope the storm doesn’t quite live up to its namesake!

I am wondering if this constitutes a sting jet, as purely by coincidence I have been reading a lot about sting jets, especially in relation to the ’87 storm, recently. A similar pattern was seen there, and again the South was the first and worst area to be hit.

The ’87 storm was said to be caused by one of these sting jets – a sting in the tail of the cyclone, which at the time was very unexpected and caught even the meteorologists off-guard.

As seen by the ’87 event, storms like this at the end of October are quite common. A large part of it has to do with the way the jet stream is deflected as the seasons change. The changing ocean temperatures as the Northern hemisphere gets colder affects convection, and can cause eddies to form at the polar front (which Britain is in the path of). The boundary between warm and cold air at the polar front is usually wavy (these are called Rossby waves) but eddies can ’pinch off’ and deflect the Jet Stream, which also travels along the Polar Front boundary. This makes anomalous cyclonic weather during October, and that’s the basic mechanics of it.

The Met Office also have a video out which shows the whole thing in more detail (with pretty visuals).
This is one of those storms that I can feel in my arthritic bones. It should be pretty spectacular at the very least, and relatively dangerous at the most.

Just remember the basics – don’t play in flood water, check if you’re in a flood zone (the Environment Agency has all the details) and if you are, don’t leave valuables within floodwater reach! I know for a fact that some train services (like South West Trains) are operating on reduced schedules so don’t forget to check your local services for and changes. Some travel services are actually advising people not to travel at all tomorrow, but that’s a bit optimistic for those of us with obligations like work.

The rain should start soon, tonight, and the full force of the storm should be felt tomorrow morning, especially the early hours. Stay safe!

The Spinning Twins and Bad British Weather

Met Office photo depicting twin low pressure zones locked together over the UK and Europe

Something interesting is happening in our skies.

It may not look like much from down here, where all we can see is a seemingly-endless sheet of stratocumulus, but way up there, a very strange pattern has taken shape.

The What.

Usually our British weather undergoes the following kind of pattern: a single spiral of low-pressure air sweeps in from the sea, usually from Iceland or the Gulf Stream ways, giving us rainy, ‘miserable’ weather. Then a spiral of high-pressure air moves up from Western Europe to give us more amiable weather. We alternate between the two. Which is why Britain is often rainy, with short breaks. Pretty simple.

But since last week, something interesting happened. A low pressure spiral of air passed over the UK – and got stuck. Another low pressure spiral joined it but did not move it completely out of position. Instead the spiral movements of the air sort of provided reinforcement for each other – a positive reinforcement cycle – and kept each other circulating over the same patch of land, namely, Britain and North-Western Europe.

There was even a point on the Met Office charts for late Wednesday night which showed three low pressure zones together over the UK!

While it’s not the weirdest thing in the world for there to be more than one low pressure zone in a weather pattern, it is strange for these zones to maintain each others’ presence in the same location for such a long period of time! It’s been a week now, and the charts indicate it’ll be at least another week before they manage to shift.

Check out the Met Office’s surface pressure animation for the next few days and you’ll see what I mean more clearly.

The Why.

The UK sits at the forefront of the battleground between cold polar air and warmer subtropical air. The line drawn between the two is called the Jet Stream; you’ve probably heard of this thing before in the news every so often.

Well, something the Jet Stream does is it undergoes these oscillations: wave-like patterns which make it change position. You might have heard of the North Atlantic Oscillation (hint: it’s also the name of a band) but what we’re going to focus on here is the Arctic Oscillation. Now, when the oscillation is in one phase, the Jet Stream may be located further up to the north of Scotland, drawing up warmer air over most of Britain; when the oscillation is in another phase it may be located closer to London, pushing down polar air over most of Britain.

A positive oscillation pattern is ideal – this basically means the waves in the Jet Stream are low, so it’s a lot calmer and more like a straight line, and weather is more regular. A negative oscillation is not so good. This means that the waves are much bigger in scale, so the undulations are a lot deeper and weather is more chaotic.

At the moment we’ve got what we call a neutral oscillation – which is not ‘no oscillation at all’, as you may think the name implies, but rather means it’s mid-way between positive and negative. And it’s been trending more and more towards the negative over the past decade.

This set of spinning twins is an example of this in action. The Jet Stream’s effectively turned into a Big Dipper, and a couple of low pressure zones have gotten entangled in one of the dips – right over our heads here in the UK. Lucky Britain, eh?

The Bad.

We should be operating under warmer weather more typical of British Summer Time now – and we did experience a nice unusual warm period almost a month ago now. Remember those numerous cloudless days before all this bad weather kicked off? Again, this was due to part of these natural oscillations, in which the waves were placed so that warm, high pressure Mediterranean air got ‘stuck’ over our heads for almost a week (but you never hear talk of oscillations when the weather’s good).

That warm period was a boon for plant life, and now plants seem to be suffering from this unexpected cold in many regions. Especially after another cold winter , the poor things aren’t doing too well! Same goes for animals – lamb birthing etc.

And of course, rain tends to ruin people’s outdoor plans! It’s not nice either for those with arthritis or something similar. Time to bring out the warm socks again in many cases!

The Good.

It’s probably time to admit that this is one of my favourite kinds of weather. With low pressure zones, especially when it’s got a good old combination of cold, warm and occluded fronts all bundled up together, you get a huge variety of clouds. It’s a cloud smorgasbord. Every day I have been able to revel in an array of dramatic cloudscapes, from the puffiest of cumulus towering in intensely sunlit skies, to wispy cirrus preceding walls of blanket-grey stratus clouds. Bands of rain that sweep over in only a couple of hours or even minutes, allowing you to gaze upon the raincloud leaving, with fibrous, veiled tendrils of rain trailing beneath it like some sacred shroud. Unexpected rainbows against cauliflower backdrops, huge anvil nimbuses with mammatus udders, the strangest shades of blue at sunset.

Anvil headed nimbus cloud with mammatus 'udders' hanging beneath
Anvil headed nimbus cloud with mammatus ‘udders’ hanging beneath
Strange blue skies at sunset against a creamy cloud backdrop
Strange blue skies at sunset against a creamy cloud backdrop
Storm cloud trailing virga, or wisps of rain, beneath it
Storm cloud trailing virga, or wisps of rain, beneath it
A grand cumulonimbus capillatus incus over South London
A grand cumulonimbus capillatus incus over South London
Dramatic cumulus cloudscape
Dramatic cumulus cloudscape
A natural cloud stripe
A natural cloud stripe

 

It’s beautiful.

If you need some more convincing, just check out this luscious slideshow from the BBC, displaying recent lenticular clouds over Yorkshire.

So it’s hard to tell how long it’s going to stay like this, but it isn’t forever. If anything, when the next high moves in, we will enjoy and appreciate it all the more.