31.   The heated air is less dense, which also has kept surface air pressures low.

32.   These cold pools, juxtaposed with mild surface air, destabilize the atmosphere, setting the stage for twisters.

33.   Thunderstorms will also develop in the southern Mississippi Valley on Monday as the same front interacts with an upper-level disturbance and humid surface air.

34.   Thursday, severe thunderstorm warnings were issued for parts of the Middle Atlantic states as a potent jet stream disturbance rapidly lifted moist surface air.

35.   To overcome deficiencies, strong jet-stream disturbances must be present to vigorously lift surface air.

36.   To the east, hit-or-miss strong thunderstorms will mushroom over the northern Plains as an insurgent upper-level disturbance dips south from Canada and lifts moist surface air.

37.   Two huge walk-in freezer doors at each entrance serve as airlocks to the entrance tunnel and prevent surface air from coming into the cave.

38.   Until then the surface air pressure and wind speeds of the powerful storm were only estimated.

39.   When they match, forecasters obtain estimated values for surface air pressure and wind speeds.

40.   When warm, humid surface air is lifted by an approaching cold front, it rises rapidly from the ground.