Wx Question

[Eric]

Ok, so I'm explaining weather for the first time to a student.....

I explain high and low pressure, air moves from high to low, high sinks, low rises, coriolis, etc.

I also explained convection and adiabatic cooling, stability, lapse rates....

He then made the assumption that high pressure areas are always colder than low pressure areas....that is why the low pressure areas rise he thinks.

I told him I didn't think he could make that blanket statement and that he was confusing two different topics.

What's the story? Are low pressure areas warmer than high pressure areas? If so, why would a warm front even move and rise above cold air?

Also, why can warm air hold more water vapor than cold air?

Thanks
Eric

 

[jdog78]

Here is my take on your questions.

First, the easy one...warm air is simply less dense and therefore has more space to hold water molecules.

A warm front doesn't really rise above a cold front as much as it is lifted by the cold front, which is generally heavier and faster moving. In the same line of thinking, a high pressure area is cooler and more dense while the low pressure area is warmer and less dense. I think the point of confusion occurs in the middle of winter when the weatherman tells us an area of low pressure is moving into the area and the ambient temperature is decidedly cold. But relative to an adjacent high pressure area, the cities affected by the low may experience warmer temperatures.
I'm looking at a current weather map of the US and I see a high over the upper midwest and a low over the new england states, located at approximately the same latitudes. The temps in the high area are in the high 40s with partly cloudy skies while new england is experiencing 60s and mostly cloudy skies with precip. This leads me to believe that moisture content is an important factor...since a low has less dense air which holds more moisture, and water molecules hold heat energy, I believe that the higher moisture content of a low contributes to the warmer temps.
So these are my amateur thoughts on your weather questions...if I have misspoken, I hope someone will correct me!

john