Stormy Weather

[Serial_Apologist]

Vints, always a fount of knowledge! I'll read that in a moment.
S_A, following second link via BBC to Met, it gives me two black lines and a pink blobby one (cold front? If so it should be coloured blue) between them. So ... "A cold front with TWO squall lines more than 100 miles apart would be pretty unprecedented here" Why is it unprecedented and what does it mean?

Going via the BBC site to Met Office, and on the Met Office page (bottom of) to Surface Pressure Maps, you get a nice big synoptic weather map in black and white. Click one at a time on the yellow tracker's subdivisions beneath the map, and you can follow the sequence of events from 12 midnight last night through to predictions for Thursday, Anna.

I've noticed that so-called "secondary weather systems" here in the UK usually follow pretty closely on from main ones, such as fronts. This would appear to be because what is known in the "trade" as "returning maritime polar air" moves faster around the low pressure centre - the reason being, as you can see on today's map, the parent low has tighter isobars than are ahead of the main fronts, hence the winds there are stronger than those ahead (i.e. to the south and east) of the weather system.

One reason which has been posited for these secondary features is that the cold air is not constituted as a simple airmass of more-or-less similar temperatures at ground level, but is cold air moving into air which is still to some extent warm at ground level, even after the passage of the main front(s) - or at any rate warmer than the replacement air. As this colder replacement air meets the lingering warmer air ahead, it lowers the ground temperature in a sequence of steps, each one of which is marked by a line of showers, advancing in parallel with the retreating cold front, and marked as a line without warm or cold front symbols, or namely, a squall line. As each line moves through, the temperature near ground level falls; and as it successively falls, convective (shower-generating) activity (which is dependent on a sharp temperature gradient from ground to cloud formation level) is gradually reduced, and the air stabilised.

Sometimes on a weather chart you will spot several of these squall lines pursuing the main fronts of a low pressure system. In some instances concentrations of heavy showers along the squall line can produce sufficiently severe weather, with correspondingly stronger inflows at certain points along the line than at others, as to cause significant lowering of barometric pressure at those points, which in turn can be sufficient to lead to the formation of a secondary low, or "arctic low", at that point.

A couple of years ago, following a series of TV programmes in which British storm chasers went off to America to observe thunderstorm and tornado activity over there, I was briefly in touch with an American storm chaser forum, and had the opportunity to observe in some detail differences between the conditions which lead to frontal genesis in the States and here. The factors leading to tornadic thunderstorms in America are very different from those which we have here. Air feeding into their storm-producing cold fronts to produce gigantic tornadoes originates from three sources, which we just don't have in the UK - cold, very dry air from the region of the Rockies; hot, very dry air from the California and Arizona desert regions; and hot, very moist air from the Gulf of Mexico. One thing I noticed - and this may go part way to ansering your question, though I don't have a full explanation - was that the resultant storm systems cover a much wider geographical area at any given time over there than is the case here. This may have something to do with the massive areas heated up to Tropical temperatures over the huge, almost flat American landmass, and the slack associated wind systems creating conditions in which weather systems can develop on a much bigger scale than we have here in the UK, where the influence of the Atlantic Ocean in keeping the jet stream on the move makes things happen in more concentrated forms, and generally over shorter periods of time, though, tbh, this is conjecture on my part.

[handsomefortune]

first break from rain ALL day..... really vile weather up till now.

[salymap]

After days of "soupy" weather, we're having a taste of autumn today. The sun is bright, air cool, no humidity, crickets and cicadas are humming away. I'm looking forward to September and our mini-vacation in Vermont.

Quite chilly and very wet here today marthe. When do you go to Vermont? Have alovely time when you get there.
I don't go anywhere now but a cousin I grew up with is coming over from Oz next week and will be around for three short weeks only, some here and some time in other parts ofthe country. He is the nearest I have to a younger brother and it will be great to see him. He went out on the £10 scheme 40 years ago, last visited us in 2005.

[Serial_Apologist]

Having read vint's link - it was a fireball according to descriptions (flaming with a tail) but the sound was really loud and there were vibrations after but the link says it's not really a sonic boom. So would it have fallen to earth, slowly disintegrated or imploded into a shower of meteorites? I'm now worried about the two squall lines, combined with the meteorite, is this the end of the world?

(Surpised at the kids being a nuisance in your basement area S_A, Dulwich is really posh area with the College and everything isn't it?)

Yes but I live on the edge of the posh part!

[Anna]

Going via the BBC site to Met Office, and on the Met Office page (bottom of) to Surface Pressure Maps, you get a nice big synoptic weather map in black and white. Click one at a time on the yellow tracker's subdivisions beneath the map, and you can follow the sequence of events from 12 midnight last night through to predictions for Thursday, Anna.

Got it, finally, the black and white pressure isobar thingy!! It's really quite fascinating reading your posts, and trying to predict the weather, but I need to read the symbols before I even have an understanding. I guess, going back to school geography lessons, it's pretty much the same as contour lines, in a way, building up.
I will re-read your post later on and try and absorb your intelligence!

[Serial_Apologist]

Got it, finally, the black and white pressure isobar thingy!! It's really quite fascinating reading your posts, and trying to predict the weather, but I need to read the symbols before I even have an understanding. I guess, going back to school geography lessons, it's pretty much the same as contour lines, in a way, building up.
I will re-read your post later on and try and absorb your intelligence!

There's a way of describing the world's wind circulation patterns that even someone of my minimal intelligence & lack of scientific knowledge can understand.

The Tropical zone is the most important part, because that is where the sun's power is at its most concentrated.

Imagine the world is standing stock still, the sun heating the tropical zone more than anywhere else.

All that heat at ground level has to go somewhere: upwards. It reaches the dewpoint level - the level where moisture can condense onto dust particles. Clouds form and get higher and higher - there's nothing to stop them - up to the Troposphere. Air is sucked in from north and south of the Tropical zone to replace the rising air, but the rising air rises faster than it is replaced, so air pressure at ground level becomes lower than in the subtropical zones.

All that hot risen air has to go somewhere when it hits the Troposphere, so it moves north and south, at great heights, away from the Tropical zone. Some of it descends in the subtropical zones, causing the pressure near ground level to rise - so we have the subtropical high belts, such as the oft-mentiooned Azores High. These high pressure systems leak air back into the tropical zone - to help keep the tropical low pressure zone going - but also outwards towards the poles. Cold air over the poles leads to the formation of polar high pressure systems, which in turn leak cold air outwards towards the subtropics.

This cold, polar air meets the warm, subtropical air, roughly at our latitude, and that of New Zealand in the southern hemisphere. Being heavier, the cold air undercuts the warm air. Either the warm air advances, riding smoothly up over the cold air in something that looks like a wedge of cheese viewed from the side - a warm front, or the cold air advances and undercuts the warm air - a cold front.

Two things complicate this.

1) The Earth is neither all land, or all sea. Air heats up or cools down land masses faster than water. The distribution and morphology of sea and land masses has an effect on where and when weather happens at these airmass boundaries.

2) The Earth's spin has the effect of deflecting the movement of air from cold to hot and back again, thus creating eddies and spirals, which tend to gravitate predominantly towards the airmass boundaries, creating both the ocean currents and a continuous cycle of generating and dying low pressure zones. This can be simulated by stirring a washing up bowlful of soapy water and watching the soap patches form into spirals and then disperse. The warm and cold air zones, in interactive combination with Earth's gravity, together with the eddying air currents, and the distribution of land masses, mountain barriers, seas and oceans, create what is known as the Coriolis Effect, i.e. the tendency for the deflected air, at high levels, to concentrate into narrow streams above where the warm and cold airmasses of polar and subtropical origin meet, or overlap. These narrow streams are the Jet Streams which circle Earth, more-or-less at our latutude.

The easiest way to simulate the Coriolis Effect is to take a bowl, drill a hole at its centre, and secure it to a board with a bolt and nut. The bowl shape simulates Earth's gravitational pull. Place a small marble in the bowl and spin the bowl. The gravitational pull of the bowl's rising sides will prevent the marble's escaping from the bowl's confines as long as the speed of the spin applied does not exceed a given limit - imitating the Earth's gravitational pull's ability to contain the planet's air movements from flying off centrifugally. By maintaining a constant revolving speed, what is interesting is that the marble inside the revolving bowl moves in a regular oscillatory wave pattern between the bowls centre and perimeter. Gravity has an equivalent effect on the jet streams. Other factors then come into play to determine that the Earth's jet streams do not assume the same constant, wavelike movements.

But here we're entering on the borderlands of Chaos Theory, where it all gets interesting, ahem...

Nuff for now...

[salymap]

HOW MUCH SLEEP DO YOU NEED/GET?

I seem to have four hours now and am always tired but can't sleep more than that. I know Mrs T ran the country on that amount of sleep but I am no MT.



on topic, murky, damp and cold. Have had heating on for the first time. bestio

[gurnemanz]

Got it, finally, the black and white pressure isobar thingy!! It's really quite fascinating reading your posts, and trying to predict the weather, but I need to read the symbols before I even have an understanding. I guess, going back to school geography lessons, it's pretty much the same as contour lines, in a way, building up.
I will re-read your post later on and try and absorb your intelligence!

Meteox do quite a neat 3 day rainfall prediction for Europe.

http://www.meteox.com/forecastloop.aspx?type=1

[mangerton]

HOW MUCH SLEEP DO YOU NEED/GET?

I seem to have four hours now and am always tired but can't sleep more than that. I know Mrs T ran the country on that amount of sleep but I am no MT.

salymap, many people thought she ruined the country on four hours' sleep.

I too suffer from insomnia from time to time, and I know it's a miserable thing. I go to sleep, then wake up about 3 am. I've tried everything - go to bed early, go to bed late. Hot drink before bed, no drink before bed. Nothing seems to make any difference.

[salymap]

salymap, many people thought she ruined the country on four hours' sleep.

I too suffer from insomnia from time to time, and I know it's a miserable thing. I go to sleep, then wake up about 3 am. I've tried everything - go to bed early, go to bed late. Hot drink before bed, no drink before bed. Nothing seems to make any difference.

I know. And I often turn to the laptop, although the advice is always DON'T go on line. And dear old Windows is 'not responding' again. Grrr.

[amateur51]

salymap, many people thought she ruined the country on four hours' sleep.

I too suffer from insomnia from time to time, and I know it's a miserable thing. I go to sleep, then wake up about 3 am. I've tried everything - go to bed early, go to bed late. Hot drink before bed, no drink before bed. Nothing seems to make any difference.

BBC World Service almost inaudibly on a transistor radio on the mattress next to your head - the concentration required to make out the words sends me back off to Noddington Junction pretty quickly.

[Flosshilde]

I know. And I often turn to the laptop, although the advice is always DON'T go on line. And dear old Windows is 'not responding' again. Grrr.

I'm an insomniac too. When I was younger I could use the time writing or doing something useful for two or three hours & then go back to bed & be as fresh as a daisy the next day. Now, by lunchtime my petals have dropped off.

[Flosshilde]

But back to the weather - lovely sunny day here, but autumn is in the air - nippy this morning, & despite the sun I had to wear a jacket.

[amateur51]

Street lights have just come on, check the time of this post

[Flosshilde]

My partner I were commenting with surprise & dismay last night that it was dark by 9.00pm! Still broad daylight at the moment here I think it will change in September, & we'll be darker before you are.