The polar airmass has low dewpoints, cold temperatures and a high degree of stability. The denseness of cP air creates surface high pressure and a trough aloft, especially when cP air moves into lower latitudes. Precipitation in association with cP air is usually light due to the dryness and low moisture capacity of the air. Precipitation is most common on the "edges" of cP air, especially where it intersects and displaces mT air. Precipitation within a cP air mass is elevated and dynamically induced. These dynamical uplift mechanisms include jet streaks, isentropic lifting and positive differential vorticity advection. Cold surface temperatures and a dry boundary layer inhibit thermodynamic convection. cP air modifies rapidly as it moves to the South. The dewpoints remain low but the temperature of this airmass increases when moving South due to the following: warmer soil temperature, a shallower airmass, higher sun angles and a lack of surface snow cover. cP air will modify less rapidly if soil temperatures are abnormally low to the south (especially if surface snow cover exists). On some occasions the subtropical jet will "isentropically lift over" the shallow cP air. If this occurs, the cP air will modify less rapidly due to a much-reduced solar heating. Once cP air modifies significantly it no longer makes sense to label it Polar air. After modification, cP air becomes modified cP air or modified mid-latitude continental air.