Ok, QFE is the actual pressure at airfield. QNH is derived from the actual pressure at airfield reduced to sea level using ISA. Now how do you anticipate a high pressure and low pressure air at the airfield using QNH? Should I compare the actual pressure at airfield (QFE) to the ISA pressure and if it is a high value then it's high pressure and vice versa? Or is there a simplest way?