A positive lifted index means that a parcel of air, if lifted, would be COLDER than the surrounding air at 500mb. The air is, therefore, stable and would resist vertical motion. Large positive values (+8) would normally indicate very stable air.
Pressure is equal to the ratio of thrust to the area in contact. Upthrust is a force exerted by the fluids on an object placed in the fluid . Upthrust acts in upward direction.
