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?
Not quite sure what question you are asking here.
Why would you want to anticipate a "high pressure and low pressure at the airfield"?
At a high elevation airport (for example Mexico which is circa 7,000 feet above sea level) the QFE would be about 256 millibars less than the QNH. From a weather perspective the lines on a weather chart (isobars) join places of equal barometric pressure at sea level (let's say QNH to keep it simple) - so if you want to know whether the pressure (from a weather perspective) is "high" or "low" best to use QNH.
Hope this helps