Sunday, January 16, 2011

Forecast Upper Air Soundings for the Tues 18 Jan Winter Weather Event

The individual white charts that I posted below are called "soundings" or SkewT's; in this case a forecast sounding from a particular model (in this case the UK) for both a particular location and specific time.

In simplicity it is a plot of air temperature (the red line) and dew point temperature (the green line) versus height. Height is plotted not in feet but millibars. Along the right vertical axis going up is the forecast wind speed (in knots) and direction (in degrees). On the direction shaft you will see lines called barbs)a full barb is - to 10kts, a 1/2 barb is 5kts and pennants are 50 kts. So for example if you had a pennant followed by two full barbs and a half-barb the wind speed would 75kts (NOTE: I use knots on my forecast sounding data, some plots use meters/sec)

The far right data blocks show forecast instability parameters, shear and helicity/holicity values as well as layer thickness'. Thickness is basically the distance between two pressure levels. The greater the distance between levels the higher the thickness and the warmer the air. The less the distance between the layers the "colder" the air. Thickness data can be useful in determining precipitation type (or p-type). I'll post a brief write-up on how you can use thickness info to forecast p-type in another blog update.

More on SkewT's can be found here: How to read a SkewT and here More on SkewT

No comments:

Post a Comment

Thank you for taking the time to comment, I will answer as soon as I can.