Spring has sprung! Has it?!

[Stillhomewardbound]

Today is the first day of Spring. Apparently.

Here's what my inside chap at the Met Office is saying:

"The seasonal equinoxi were once markers in the UK's meteorological calendar, according to which, broadly speaking, folk could notice distinct changes in the weather, usually as per a three month span. These days they are recalled as a quaint and outdated device in a modern world where all four seasons can be presented within a single afternoon and entire years can be themed according to a single season. The current theme of Winter is now enjoying its fourth year in a row. In this way, anomalies such as mild, balmy, warm and fair have been able to be ironed out."

[Serial_Apologist]

Having studied the weather for some 55 years, and intermittently kept a diary of daily weather events during that time, I do feel that the past 3 years do represent a qualitative shift in weather patterns from those which previously gave us our characteristic climate.

For one thing, gone now seems to be the predominance of westerly and south-westerly winds.

Secondly, the equinoxial shift referred to in SHB's quote represents the decline in the "Siberian high" coinciding with the northward movement of the subtropical high pressure zones, as locally represented by the "Azores high".

It has always been normal for high pressure to dominate over the North Pole. In winter this is usually a larger semi-permanent feature than in summer. A much larger system of high pressure, however, develops every November over the Siberian landmass, marking the coldest region of the northern hemisphere. In average winters of the past the Siberian high has not extended its influence much further west than Germany; most of our cold spells originate from a southward extension of the Arctic high behind a family of depressions, bringing snow showers born of northerly winds, especially to Scotland and Northern Ireland, the Pennines and North York Moors, and temporary prolonged snow ahead of advancing depressions following in from the west. Colder weather than this results from westward extensions of the Siberian high, because the advancing air has had less time and distance to warm up by contact with warmer sea surfaces than the northerly winds. In such situations the coldest temperatures are often experienced in southern England, with winds directly from the Continent.

The coldest winters of all, such as this one has been, result from the Arctic and Siberian highs joining forces.

Normally, in the past, it is around the Spring Equinox that the Siberian high retreats and shrinks, often leaving a small subcell of itself centred over the snowfields of Norway, which can last until the beginning of June. This phenomenon is responsible for a high frequency of north easterly winds affecting the east coast at this time of year. What is noticeably unusual this year - although it has been to a lesser degree characteristic of the past 3 years - has been a prolongation in the persistence and strength of both the Arctic and Siberian highs, and the tendency of the former to extend very strong ridges of high pressure between east-moving Atlantic depressions, bringing them to a halt in mid-Atlantic, and diverting the jet stream (which carries them in a normally eastward direction) further to the south than would, in the past, have been regular. New depressions, forming ahead of the stalled mid-Atlantic low, then shoot south-eastwards, across Iberia, from whence they re-intensify on hitting the warmer seas of the Mediterranean. This BTW has always been a common feature in spring, when holidaymakers anticipating an early break from winter by taking a Mediterranean break have often been disappointed!

Anticyclones - high pressure zones - are associated with settled weather. But they are in fact the "bullies" of the atmospheric circulation system; as passing systems they can give us warm sunshine in summer and fog and frost in winter; but, once in place for any considerable lengh of time, they are a block against approaching depressions, depriving locations under their sway of sometimes much-needed rainfall. Added to which, the actual shape and location of any given high pressure system determines what kind of weather it brings, dependent on where one is in relation to it.

It is this formation of "blocking highs" that has become a prominent characteristic of the past 3 years. The "experts" are still not sure as to the cause, but a theory that has gathered much support has been the effect of global warming on releasing increasing amounts of fresh meltwater into the northern reaches of the Pacific and Atlantic oceans. This is thought to be pushing the jet stream further south with greater regularity and persistence than has previously been the case, although the evidence is still largely empirical and the precise mechanism has yet to be understood.

[Eine Alpensinfonie]

Silly me. I thought the equinox was tomorrow.

[kernelbogey]

Spring is sprung,
the grass is riz,
I wonder where the boidies is.
They say the boid is on the wing.
But that's absoid.
The wing is on the boid.

Can't find the attribution of this though apparently neither Ogden Nash nor e.e. cummings. Just always occurs to me when I hear the words of this OP!

[Belgrove]

Thanks for your fascinating and penetrating analysis Serial_Apologist. Do you happen to know the mechanism by which the ocean temperature influences the location of the jet stream?

[Stillhomewardbound]

Indeed, SA. A most illuminating precis.

[johncorrigan]

Indeed, SA. A most illuminating precis.

Completely agree - very interesting SA - a couple of weeks back spring was on the way - the birds started singing the daffodils shot through, and then winter returned - will they all just go back to a hibernation setting - I certainly feel like doing that. More snow out there this morning.

[salymap]

Spring is sprung,
the grass is riz,
I wonder where the boidies is.
They say the boid is on the wing.
But that's absoid.
The wing is on the boid.

Can't find the attribution of this though apparently neither Ogden Nash nor e.e. cummings. Just always occurs to me when I hear the words of this OP!

I thought of that too kernel. In fact I was trying to compose a version of my own, incorporating the word
'baroque'.

[An_Inspector_Calls]

For one thing, gone now seems to be the predominance of westerly and south-westerly winds.

My gut impression agrees with this, but then plotting the wind rose from last year's weather station data tells a different story (damned if I can post the image of this). The south-westerlies are still dominant, followed by the usual blows from the north east. Perhaps this is distorted by those periods of high pressure which are usually associated with low temperatures and low wind speeds (good idea erecting windmills?) since calms are not usually well-displayed on a wind rose?

[mangerton]

Spring is sprung,
the grass is riz,
I wonder where the boidies is.
They say the boid is on the wing.
But that's absoid.
The wing is on the boid.

Can't find the attribution of this though apparently neither Ogden Nash nor e.e. cummings. Just always occurs to me when I hear the words of this OP!

I first read it in Verse and Worse ed. Arnold Silcock. I'll try to remember to look it up when I get home this evening.

[eighthobstruction]

What happening to the Jet Stream nowadays....??....please....

[Serial_Apologist]

Thanks for your fascinating and penetrating analysis Serial_Apologist. Do you happen to know the mechanism by which the ocean temperature influences the location of the jet stream?

You're all welcome!

Quite honestly there's an awful lot I don't understand in the science. For instance, which comes first, the course of the ocean currents or the jet stream (?) From what I can understand the relationship between them is two-way. To have become a meteorologist - which is what I would have liked as a child - would have required a far greater aptitude for maths than I possess.

I did coach the A Level Geog class on the basics of weather systems when it became obvious our schoolteacher didn't know which way wind circulates around cyclones and anticyclones.

[Serial_Apologist]

What happening to the Jet Stream nowadays....??....please....

It's still there - it never goes away - it's just travelling much further to the south and for much longer than it used to do, apparently.

[greenilex]

Equinox again, though I haven't checked exactly when...cruellest month soon, nevertheless hearty wishes to all for a prosperous year!

[ferneyhoughgeliebte]

Equinox again, though I haven't checked exactly when...cruellest month soon, nevertheless hearty wishes to all for a prosperous year!

And to you, too, greenilex Yesterday, according to Google - and the clocks go forward in the early hours of Sunday, so some light evenings ahead of us.