PDA

View Full Version : ELevation Temprature change



VT9092
07-23-2008, 06:40 PM
Hi everybody,
First post here. I live in Virginia and have a simple question about elevation and temprature change. Currently I live at 2100 feet and there is a local mountain that at its highest is 4368 feet. Thats about a 2200 difference. My question is what conditions must be present for the most drastic of temp differences? Some days its only a couple of degrees difference, while other days it can be 10-15 degrees different. does it have to do with low and high pressure systems??
Thank You

Bill O
07-23-2008, 09:53 PM
It has to do with many factors. Sunny days are likely to have a bigger contrast with the sun warming the surface more efficiently than the air at higher elevations.

An upper level low is associated with a cold pool of air aloft, that would increase the temperature difference.

Its a self limiting factor though. The temperatures can't diverge forever, otherwise the warm air at the surface would escape the atmosphere because hot air rises. Anytime the temperature decreases more than 9.8C per 1,000 meters the surface air will rise and cool until it reaches an equilibrium.

You see the smallest temperature difference when the air is saturated (when its foggy or cloudy).

On a clear night its common to get an inversion, where the temperature rises with elevation.

JimS
07-24-2008, 12:46 PM
Bill has hit all the major meteological factors that go into the complex atmosphere. But in an ideal world, the formulas that our thermodynamics textbooks 'will' 'work' 'perfectly'.

What does an ideal world look like atmospherically. Air that lifts from the surfact to elevation with no outside entrainment, loss of radiation, and normal expansion due to pressure.

If we follow these rules...near surface averages tell us that an isolated parcel of air will cool adiabatically at a rate of ~5.5F until it reaches saturation.

Once it saturates, the phase change releasing latent heat slows the rate to roughly 3.5F per thousand feet.

Therefore, on a clear day, you should see ~10F change on the mountain from your house. For normal conditions that include actual weather that the textbooks 'ignore' see post above...

VT9092
07-24-2008, 04:16 PM
Lots of good imformtion!
The forecst low for my area tonight is 52 degrees...Todays weather has been sunny with cirrus clouds(H4) and winds of 10-15mph..so with weather like this tonight when I go camping I could see 42 degree weather at some point before dawn right?

JimS
07-24-2008, 11:03 PM
Perhaps...perhaps not. It depends on whether or not those winds die...Refer to BillO's last line...

If the winds die off, the ground will radiate to 52 under clear skies and light winds. This will set up a fairly common nighttime occurance called an inversion, where it is warmer a few thousand feet up than it is at the surface. With good mixing of the air with wind though...the 42 is possible.

Often times in the fall especially, but after a good cold front with high pressure building in, mount washington can be the WARMEST place in New England at 5AM...

It's very complicated, but one of the best ways to get a feel for it is to experience and debrief when you return.

VT9092
07-25-2008, 09:23 AM
Well I camped under the stars at the top of the mountain last night. It only dipped to 47 at the lowest, and like you said, it warmed up to near the same temprature as the valley below. Thanks for all the great advice!