simonjk
Well-known member
Hi all,
Just sent this email to my weekend forecast subscribers. Thought readers of the forum might be interested in it as well.
An interesting situation developing late on this week, and one that nicely illustrates the effects of upper air meteorology.
The 500hPa charts (about 18000ft)(as shown below contain information about the height of that level (500mb, it varies with temperature. Contours are the solid lines on this chart) and the temperature (the dashed lines in degrees Celsius).
http://expert.weatheronline.co.uk/z500_frame.htm (click on 12 Fri)
Okay, first up is the chart for midday on Friday. What I want you to notice about this chart is that little kink in the isobars to the far west of the Atlantic. This is called a short-wave trough. Over the UK and Ireland is a minor ridge. The jet stream is just north of Scotland (where the contours are closest). Also, notice how the temperature contours dip to coincide with that trough to the west, hence the reason for the lower heights.
http://expert.weatheronline.co.uk/z500_frame.htm (Click on 12 Sat)
Right , next is the chart for midday Saturday. Notice how our short wave trough has “deepened” slightly, and the temperature gradients have become stronger with it. This shows a strengthening trough.
However, of real interest is what is happening behind it. See that ridge in the west Atlantic? Well, that is warm air pumping northwards. As it moves around the northern axis of the ridge its slowing down, and so the air is piling up behind it. This leads to the ridge building further. We know it’s warm air, because the temperature contours tell us.
http://expert.weatheronline.co.uk/z500_frame.htm (Click on 12 Sun)
Now we are onto the chart for Sunday. The ridge has built to the west of the UK, but the air that travelled northwards around the ridge has been force to much colder climes, i.e. Greenland and north of Iceland. This has to come south again and then flows rapidly south into central Europe. The contours are really tight east of the UK, and see how close the temperature gradients are as well.
http://expert.weatheronline.co.uk/pslv_frame.htm (click on 12 Sun)
But how does this relate to the surface chart? Well, here is the chart for midday Sunday. High pressure west of Ireland and low pressure to our east. To be honest, this looks a little simplistuic to me, although the evolution is good. I wouldn’t be surprised to find a few troughs moving down the North Sea on Sunday bringing some snow showers to eastern England and Scotland. Certainly winds near gale force here.
However, in this musing I just wanted to show you how the upper air related to the surface and how if you look at the upper chart you can get a feel for surface conditions.
Hope that’s been of interest? This is the sort of thing we look at Weather School, so if you are interested, please ask for details.
**Next Weather Schools:
Sailing (Part 1) Saturday 12th February 2005
Using & Understanding Internet Weather – Saturday 5th March
Call 01902 895252 or email simon@weatherweb.net for details**
Cheers,
Simon
Just sent this email to my weekend forecast subscribers. Thought readers of the forum might be interested in it as well.
An interesting situation developing late on this week, and one that nicely illustrates the effects of upper air meteorology.
The 500hPa charts (about 18000ft)(as shown below contain information about the height of that level (500mb, it varies with temperature. Contours are the solid lines on this chart) and the temperature (the dashed lines in degrees Celsius).
http://expert.weatheronline.co.uk/z500_frame.htm (click on 12 Fri)
Okay, first up is the chart for midday on Friday. What I want you to notice about this chart is that little kink in the isobars to the far west of the Atlantic. This is called a short-wave trough. Over the UK and Ireland is a minor ridge. The jet stream is just north of Scotland (where the contours are closest). Also, notice how the temperature contours dip to coincide with that trough to the west, hence the reason for the lower heights.
http://expert.weatheronline.co.uk/z500_frame.htm (Click on 12 Sat)
Right , next is the chart for midday Saturday. Notice how our short wave trough has “deepened” slightly, and the temperature gradients have become stronger with it. This shows a strengthening trough.
However, of real interest is what is happening behind it. See that ridge in the west Atlantic? Well, that is warm air pumping northwards. As it moves around the northern axis of the ridge its slowing down, and so the air is piling up behind it. This leads to the ridge building further. We know it’s warm air, because the temperature contours tell us.
http://expert.weatheronline.co.uk/z500_frame.htm (Click on 12 Sun)
Now we are onto the chart for Sunday. The ridge has built to the west of the UK, but the air that travelled northwards around the ridge has been force to much colder climes, i.e. Greenland and north of Iceland. This has to come south again and then flows rapidly south into central Europe. The contours are really tight east of the UK, and see how close the temperature gradients are as well.
http://expert.weatheronline.co.uk/pslv_frame.htm (click on 12 Sun)
But how does this relate to the surface chart? Well, here is the chart for midday Sunday. High pressure west of Ireland and low pressure to our east. To be honest, this looks a little simplistuic to me, although the evolution is good. I wouldn’t be surprised to find a few troughs moving down the North Sea on Sunday bringing some snow showers to eastern England and Scotland. Certainly winds near gale force here.
However, in this musing I just wanted to show you how the upper air related to the surface and how if you look at the upper chart you can get a feel for surface conditions.
Hope that’s been of interest? This is the sort of thing we look at Weather School, so if you are interested, please ask for details.
**Next Weather Schools:
Sailing (Part 1) Saturday 12th February 2005
Using & Understanding Internet Weather – Saturday 5th March
Call 01902 895252 or email simon@weatherweb.net for details**
Cheers,
Simon