A word about Thickness and Pressure

Drew and I were talking about 540hPa line in the MM5 thickness model - Had to go and do some research.

THICKNESS: The difference in height between two atmospheric pressure levels. The thickness is directly related to the average temperature in the column of air between the pressure levels (thus, higher thicknesses typically mean warmer temperatures). The most common thickness used is for the 1000-500mb layer.  At Stevens Pass's elevation, it is best to look at other thickness layers such as 1000-850 mb layer.  Mainly the 540 line.  

'Thickness' is a measure of how warm or cold a layer of the atmosphere is, usually a layer in the lowest 5 km of the troposphere; high values mean warm air, and low values mean cold air.  The 500-1000 hPa (hydrostatic Pressure also measured in mbar)value is used to define 'bulk' airmass mean temperature.   The 540hpa is the line that seperated cold air from warm air - the freezing level +-4000' .