Increasing heights usually indicate clearing weather for the period under consideration. The colour shading indicates vorticity at 500 millibars. Europe Coloured contours indicate the air temperature at the 850 millibar level in degrees Celsius. The 0 degree line is highlighted, as this is also often used as a divider between rain and snow. THe green shading indicates the relative humidity per- centage at the 850 millibar level.
High values indicate the availaability of moisture.
THe barbs indicate the direction and speed of the wind, in meters per second. The direction of the wind is parallel to the shaft with the barbs pointing into the wind. Advection of moisture by the wind can be inferred by noticing the direction and rate at which moist areas appear to be blown. Similarly, temperature advection can be inferred by noticing whether the wind is blowing cold air towards a warm region, or warm air towards a cold region.