[thedoc (OP)]

Martha Rhodes asked the Naked Scientists:































   































If cold fronts move faster than warm fronts , but cold air molecules moves slower than warm air molecules, how do they move faster?































































What do you think?

[Colin2B]

Martha Rhodes asked the Naked Scientists:
   
If cold fronts move faster than warm fronts , but cold air molecules moves slower than warm air molecules, how do they move faster?

Warm air is less dense and the cold denser air pushes under the warm air lifting it. The front is the line at ground level (usually adjusted to sea level) where the 2 air masses meet, when the cold air completely undercuts the warm air and lifts it off the ground we get what us called an occluded front.
So it has nothing to do with air molecules directly, but the colder air mass sinking and being pushed by the rotating winds in the low pressure system.
Not easy to describe without a diagram, but I hope that helps.

[alancalverd]

In a typical Atlantic cyclone, the cold air comes from the north and therefore its westerly ground speed increases as it moves south (because the earth is moving faster at lower latitudes). Conversely the warm air decelerates relative to the ground as it moves northwards. Thus the wedge of cold air appears to be moving eastwards and overtaking the warm sector.

Additionally, as the warm air tends to overlie the cold air, the "warm front" is very diffuse - the jet stream propels it forward at high altitude (hence cirrus clouds lead the front) and the low stratus follows more slowly. The cold front, however, is usually more abrupt, with the cold wedge forcing the warm moist air upwards  to form cumulus and cumulonimbus clouds in a clear sky with no top cover. 

[Pecos_Bill]

Cold air is denser than hot air. This is why the little kitty-cat bags it down into the basement instead of up into the attic in a heat wave.

Also hotter air rises by convection and the colder denser air expands in to replace it.