Weather

[Tugmistress]

anyone interested in the weather? lol ok that's a stupid question, most people in the world are interested to one degree or another. I know i have had several emails/pm's from people wanting weather stations and various forecasts, would anyone be interested in learning a little about the charts? i'll do this thread this week and see what happens.

I have spotted this in the charts for sunday 18th january, as it's monday it is highly likely to change, but which way???? for the worse or for the better? the aim of this thread is to try and explain in simple terms (i'm not the best endowed with brains) how i read the charts and do you all the forecasts/warnings etc.


the image below was taken from todays 12z (noon) charts, these have seemed the most accurate charts to go by for this location. all i use this chart for is the barometric pressure lines - the tighter they are the stronger the wind. 'T' is the centre of a low and 'H' is the centre of a high pressure. (hey it's a german site and i don't speak german so can someone educate me why the letter 'T'?)
when you have spotted the UK, you will see a very low low off to the northwest, the numbers on the lines represent the barometric pressure at sea level. (the higher your altitude is also a case of lower barometric pressure than sea level as there is not the 'stack' of air above you to compress it if that makes sense?)
the centre of the low is at 940mb (mb = millibars) and the line that is shown to cross us is at 980mb.
over time looking at my records i estimate the average barometric pressure here to be around the 995mb, so at 980mb it is still a low pressure to us here. one of the things this means is tides will be higher than published on tide tables... boat owners will be aware of this phenomenom.
the gap between the lines is what defines the wind speed, the smaller the gap, the steeper the gradient from one number to the next, the faster the wind speed.... looking at 'our line' (the 980mb) the gap is fairly large between it and 975mb, this sort of size says to me gusts of up to around 30mph, i only learnt this through looking at the current charts and reading what my anemometer was reading for actual speeds and you soon learn what gap represents what sort of speeds. if, as the week progresses and the centre of the low moves nearer to us, and stays at the same intensity, you can see the lines nearer the centre are closer together, therefore the wind speed will be greater... this is the sort of thing i watch for and then warn you all about a few days beforehand.
as for the colours on this particular chart, i have not got a clue lol




does anyone want me to carry this thread on? anyone interested in learning a new hobby? if so are you interested in the temperature charts? what can i help you with? i'll try my best and answer any questions

[davem]

Everyone appreciates the wheelie bin warnings, I'd definitely like to know more of how you do it.
Thanks
Dave

[wifie]

Great idea Tugs - I am up for learning more!

[Tugmistress]

ok, this is the same time as yesterdays chart, there are 4 differences that i am seeing ...1, the centre of the low is a little further east than yesterdays chart, 2, the centre of the low has intesified by 5mb down to 935mb, 3, the lines have tightened up a bit and finally 4, we are situated on the 965mb line.

one thing i forgot to say yesterday was the wind circling a low goes in an anti-clockwise direction, the wind circling a high goes clockwise.

With the lines at this distance apart i estimate windspeeds of around 45mph maybe gusting to 50mph from the southwest. The lower pressure will mean tide will rise higher than tide tables predict.... 965mb is roughly 30mb below our average for this area.

to factor in the swell of the sea, imagine the centre of the low is the dropping point of a rock in water, the ripples work out from the centre, then upscale this effect for the waves please note this is not always the case when there is more than one low pressure around, it depends on which is the stronger (more intense). wilth low pressure there is not the 'weight' of air to keep the swell in the sea low, it will be quite a large swell off this one.

have i confused you yet? feel free to ask anything about what i have said.

[wifie]

Cool so far and very interesting! Only thing I liked (or probs understood) in Geography was the weather! TY!

[Tugmistress]

ok same as before, 12z chart for sunday 18th at 12 noon.



the centre of the low has gone back up to 940mb, potentially showing it breaking down a wee bit a losing intensity.
we are located just inside the 975mb line, so a potential barometric pressure of 974mb for us at this time frame.
the lines over os have opened up, thus the wind speed will not be as great, at this agp around the 10mph area.
the centre of the low has also moved slightly north, again reducing it's affect on us here.

it's now wednesday, this chart is for sunday coming, that's 4 days away and more than likely more or less what will happen, but i'll continue to do the charts up to and including saturday to show you even close up that things can sometimes change from what is usually referred to as 'reliable data'.

[kas]

Count me in, I spend ages on the netweather forums, yet have no idea what on earth they are on about half the time.

Thanks Tuggs.

[wifie]

Still hingin in here Tugs! TY!

[ShelleyCowie]

Tugs how do u do it! I have read through everything u have written at least 3 times!! Still cana make sense o some o it!

[Tugmistress]

Tugs how do u do it! I have read through everything u have written at least 3 times!! Still cana make sense o some o it!

no worries shelley, tell the first thing that you don't understand and i'll try to explain it to you

[Tugmistress]

ok, todays update ...
12z chart for 12 noon sunday 18th january 2009


pretty similar to yesterdays chart - low further to the east, smaller gap in the lines so a bit windier, maybe 20mph ish but we are still sat at 975mb, centre of the low now at 950mb so less intense.

so at this point it is looking like 90% that this is what will happen

Please note, there is a warning about to come out from me about this low but for a bit sooner than sunday lunch time

[wifie]

A friend suggests tief for yer "T" Tugs - means deep!

[Tugmistress]

thank you wifie, yes that would make sense, instead of high and low, high and deep, same difference really

[ShelleyCowie]

Tugs its the MB (millibars) bit i just cant seem to get! I understand about the direction of wind and about the lines being closer together tho!

[Tugmistress]

Tugs its the MB (millibars) bit i just cant seem to get! I understand about the direction of wind and about the lines being closer together tho!

ok no problem let's see if we can help

millibars are just a number, they let you know how low a low is or how high a high is. the 'average' number for the change over from high to low on charts seems to be around 1015 so we will use that figure for now.(forget the millibars at the moment).
so anything lower than 1015 beecomes a low (pressure) and anything above 1015 becomes high (pressure).

the millibars is just one way of measuring pressure, another method with another set of numbers that i don't understand is done in inches.
hope that has helped to make a bit more sense for you.

[Tugmistress]

okay folks, you can see by todays 12z chart for 12 noon on sunday that there are still little differences.

the centre of the low has backed off a bit, so it shows the system is moving slower than thought yesterday, we are still just inside the 975mb line, but we are now at the beginning of the line tightening after a 'loose lump' of slower wind speeds. this means we will find it gusty probably to around 30mph from the south southwest. the centre has dropped back down again to 940mb so it's quite a stable system that is sure to happen, things are pretty much set now - 95%

[ShelleyCowie]

ok no problem let's see if we can help

millibars are just a number, they let you know how low a low is or how high a high is. the 'average' number for the change over from high to low on charts seems to be around 1015 so we will use that figure for now.(forget the millibars at the moment).
so anything lower than 1015 beecomes a low (pressure) and anything above 1015 becomes high (pressure).

the millibars is just one way of measuring pressure, another method with another set of numbers that i don't understand is done in inches.
hope that has helped to make a bit more sense for you.

Ahh thats better! I was thinking of it as a complete measurement but u broke it down for me there! Thank u!

[Tugmistress]

as long as you think that's helped then that's great

ok on to todays, the last before we see what actually happens.

the centre of the low is still the same intensity, but it has 'slowed down' as it is a little further south than yesterdays chart, we are now around the 970mb line with a wind from the southwest getting to around 35mph.

Hope you have followed and understood what i have been saying, and most important of all i have not bored you all to tears

[ShelleyCowie]

Keep em comin Tugs! Im enjoying reading this thread! Tryin to explain to my OH

[Tom Cornwall]

tugmistress, did u work, in a previous life, for the Met Office,...I worked for them for 35 years and find your stuff very interesting(in a good way)..keep up the good work