BLUEMOMENT

Hi again,

Today’s midday upper air sounding for Nottingham is a great example of an ascent through winter anticyclonic stratocumulus cloud.

The sounding is here http://expert.weatheronline.co.uk/cgi-b ... bdc5ba7ee5

Essentially the skew-t (or tephigram) is simply a diagram showing height against temperature. Height is measured in millibars (shown down the left hand side) and displayed on the chart as 300, 400, 500 etc…

The diagonal light blue lines are the isoterms (temperature lines). Two actual temperature lines are shown, the thick red one is the dry-bulb temperature measured as the radiosonde ascended and the thick blue line (to theleft of the red one) is the dewpoint depression line.

The closer together the red and blue line, the more saturated the air, so where they touch the balloon was passing through cloud.

You can see from this skew-t for midday today (Sunday) that the radiosonde entered cloud at about 870mb and then left the cloud at about 810mb. Now, 1mb=30ft (approx) so we can say that the cloud was about 1800ft thick (quite a depth and hence the reason for snow grains falling in many parts of the Midlands today).

Notice how the temperature rises sharply above the cloud layer, this is known as an inversion (where temperatures rises instead of falls with height).

If one were to fly through this situation today there would have been haze and cold conditions on take-off, snow grains falling as one ascended, severe icing on an aircraft as it passed through the cluod (because the temperature is well below freezing), but then on passing through the 1800ft depth of cloud one would have emerged into clear blue skies (apart from a bit of cirrus above).

Hope this has been useful and shows a little of what a skew-t diagram can show.
We cover more of these on Weather School. Visit http://expert.weatheronline.co.uk/daten ... temps.html
To view them yourself.

Best wishes,
Simon

_________________
Simon Keeling, PhD MSc, FRMetS
My new book The Pocket Weather Forecaster is out now. Read sample pages here.
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