Snow Forecast

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Precip snow level

E potent temp

Thickness

Dew Point Temp

Temp 850hPa

Temp 500hPa
Gfs 500hPa Geopotential Height, Surface Level Pressure, Relative Topography H500 H100 source:http://wetter3.de                                                                                                  
White lines: MSLP isobars (units = hPa / interval = 5 hPa)
Dark grey/dash & double-dot lines: thickness isopleths for the layer (500-1000) hPa. (units = dekametres [dam] / interval = 18 dam)
Colour shading:  colour coded as at scale by diagram. (units = dam / interval = 4 dam). Orange/Red high values - blue/indigo etc., low values.
Black line: the 552 dam contour (of the 500 hPa surface) - highlighted as the approx. median value to trace major troughs/ridges in pattern.

Some critical values for thickness if precipitation is expected (table of Murray-1959). 

Over Low Countries (< 300m):

Thickness / 2 meter temperature  -1 0 1 2 3 4
516            
522            
528            
534            

Legend

   >90 %
   50-90 %
   10-50 %
   < 10 %
SOURCE:http://www.skystef.be

1000 - 500 mb Thickness
(elevations less than 1000 feet)
5,340 gpm Greater than 50%
5,400 gpm 50% of time snow occurs
5,460 gpm Less than 50%
1000 - 700 mb Thickness
(elevations less than 1000 feet)
2,820 gpm Snow very likely
2,840 gpm Snow likely
2,860 gpm Snow not likely
850 - 700 mb Thickness
(elevations less than 1000 feet)
1,525 gpm Subfreezing layer
1,540 gpm All precip types possible
1,555 gpm Complete melting in layer
1000 - 850 mb Thickness
(elevations less than 1000 feet)
1,290 gpm Layer below freezing
1,300 gpm All precip types possible
1,310 gpm Rain is favored

  SOURCE:http://www.theweatherprediction.com        http://www.crh.noaa.gov/lmk/soo/docu/precip_type.php