Some of the fundamentals of orographic enhancement:
Presuming you want to know about orographic enhancement of rainfall, the concept of the orography is very important! The fact that there is an impermeable barrier which air cannot flow through, or flow under, means that air is forced to rise. When air rises, it cools by adiabatic expansion, and if cooled sufficiently it will form clouds and rain, or cause an enhancement in the rain that may already be falling as more moisture is "wrung out" of the air.
There are several factors which influence the degree of enhancement, but the big three that forecasters watch out for are:
A flow that has a large component perpendicular to the peaks of the orography, which means that it is forced to rise as quickly as possible.
A flow that is strong, the stronger the flow the more moisture will be released over a given amount of time.
A flow that is warm and moist (characterised by values of 850hPa theta W of around 15 or more). The moister it is, the closer to saturation it is, and the larger the effect will be of lifting over orography. The warmer it is, the more moisture it will be able to hold in the first place, meaning more can be released.
These conditions are most commonly found within the "warm conveyor belt" of storm systems, and in certain conditions can be responsible for widespread floodings, like the Cumbrian floods of last year.)
Good Luck with your research! :)
http://en.wikipedia.org/wiki/2009_Great_Britain_and_Ireland_floods - about the floods
http://en.wikipedia.org/wiki/Wet-bulb_potential_temperature - about theta W
http://en.wikipedia.org/wiki/Norwegian_cyclone_model#Conveyor_belt - about conveyors