The maritime tropical air mass is most often felt in the Southeast U.S. with respect to the United States. In the winter this air mass is shoved toward the equator but in summer it can cover much of the U.S. east of the Rockies. This air mass results from the warm waters of the Gulf of Mexico and Gulf Stream and abundant high angle sunshine. The warm waters in this region evaporate an enormous volume of water. Cold water currents tend to stabilize the atmosphere and produce little evaporation while warm waters destabilize the atmosphere and add moisture. The warm waters conduct heat toward the low levels of the atmosphere. Temperatures in this air mass warm to highs in the 80's and 90's in the summer and the 60's and 70's in winter. High dewpoints (generally greater than 50 F) characterize mT air. The majority of U.S. thunderstorm activity develops within the mT airmass, most being by way of scattered thermodynamic thunderstorms and thunderstorms out ahead of fronts. As the maritime tropical airmass moves over land it begins to "pick up" characteristics of a continental climate. This is particularly true when the mT airmass moves toward the North. The mT airmass modifies due to lower sun angles, drier land below, and cooler land below.