Answer to Question 1
ANSWER: In winter, cold fronts are well developed with strong temperature contrasts. When warm, humid mT air is drawn northward ahead of the front the warm air is lifted, often producing stormy weather. In winter, along a warm front the air is usually stable as warm air lies above cold air. In summer, along a warm front, warm, humid, unstable air rides up and over only slightly cooler surface air. Often the rising unstable air is able to produce towering clouds, showers, and even thunderstorms.
Answer to Question 2
ANSWER: After the air mass spends some time over its source region, it usually begins to move in response to the winds aloft. As it moves away from its source region, it encounters surfaces that may be warmer or colder than itself. When the air mass is colder than the underlying surface, it is warmed from below, which results in a steeper lapse rate and instability at low levels. In this case, increased convection and turbulent mixing near the surface usually produce good visibility, cumuliform clouds, and showers of rain or snow. On the other hand, when the air mass is warmer than the surface below, the lower layers are chilled by contact with the cold earth. Warm air above cooler air produces a stable lapse rate with little vertical mixing. This causes the accumulation of dust, smoke, and pollutants, which restricts surface visibilities. In moist air, stratiform clouds accompanied by drizzle or fog may form.
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