Here is the answer from DJ which was in the other forum ...
Sorry for noob question here - can you tell me what 'thickness' is?
Chris the thickness value is the depth of atmosphere between two pressure levels. The most common one is the distance between the 1000hPa and 500hPa levels. The 1000hPa level is near the ground and the 500hPa level is the middle (by mass) of the atmosphere. This is usually marked by dotted lines on model forecast charts.
Turns out the thickness values is strongly related to the temperature of the atmosphere through a relationship called the hypsometric equation (en.wikipedia.org/wiki/Hypsometric_equation). Each 20m change in thickness is close to 1C change the average temperature of the 1000 to 500 hPa layer.
The thickness is usually reported in metres (a typical 500-1000hPa value will range from 5300 in winter and 4800 in summer) or 10s of metres (dm) with values typically ranging from 530 to 480.
For the Dandenongs we tend to find a 532dm thickness is cold enough for snow to around 600m. A 526dm thickness is about 3C cooler and will see snow to 100-200m. Of course, every situation is different and sometimes the distribution of temperature through the 1000 to 500hPa level can be very different from the norm. I've seen snow in the Dandenongs with thickness values as high as 540 and seen it rain with thickness values of 528.
At the other extreme a thickness value of 576dm in summer will see near 40C in southern Australia.
Hope this helps.
