Skew T : Masterclass 2 of 4Added : Friday at 20:03 For this master class we will be looking at moisture in the atmosphere. Skew-T charts are just perfect for showing you where cloud will be in the atmosphere and also how much.
Take a look at the following chart :-
The first thing you will notice is how close all of the lines are. This means that the air will be saturated from around 700mb right up to 300mb (as the red and blue lines are running next to each other).
This type of chart would probably tell you that a low pressure system is moving through with plenty of cloud and you are right! How heavy will the rain be? Well if you look at the orange line you'll see that it is on the right of the blue/red lines near the surface, but to the left of the lines further up in the atmosphere.
When the red line is to the left of the orange line then it means that the air is cooling faster than it should (the lapse rate) so air will be rising faster. But higher in the atmosphere the orange line changes side and this would mean that the parcel of air rising would slow down.
In a nutshell, we would expect some moderate rain to fall from this Skew-T chart.
Once the weather system has passed through then we would expect to be in sunshine and showers. This is the forecast Skew-T chart for that and you can see a classic Skew-T chart for sunshine and showers.
The red line is to the left of the orange line which means that as a parcel of air rises it will always be a little cooler than it should be based on the lapse rate. The blue line (or dew point) is not far off the red line indicating moisture in the atmosphere is available.
This is a perfect chart to show a typical sunshine and showers set up.
So what would high pressure look like?
This is not the best example, but here you go :-
The main things you'll notice is that the blue line kicks away to the left at 800mb, this is a dry layer in the atmosphere. But also, the red line is always to the right of the orange line indicating that the air rising will always be a little warmer than it should be and will start to descend.
Also, if you look at around 800mb you'll see the red line go back to the right, this is an inversion as the air temperature increases for a bit which would stop air rising from the surface due to daytime heating.
METEOROLOGIST : MARSH |