(Senior Storm Chaser)
Thu May 30 2002 09:59 PM
Question for the Meteorologists out there...

Is there a laymen FAQ out there about the different measurements one encounters and what they signify? It's pretty obvious when you look at a sea level pressure forecast, but the 200mb, 500mb, 800mb etc. are a little fuzzy to me. And what are the norms? Often you hear about the 500mb height line. Is this a point in the atmosphere where measurements are derived from or do they base interpretations off of seasonal norms or whatever?

Thanks for any tips or info.


Fri May 31 2002 12:24 PM
Re: Question for the Meteorologists out there...

Not really, but I'll try to explain...

Because the surface of the earth is NOT uniform (i.e. it varies in altitude) we use pressure readings at the surface. However, above the surface of the earth, we use CONSTANT PRESSURE levels instead....that is what is meant by the 925, 850 etc. It is algebraicly more convienient to use constant pressure instead of altitude. So when you see the term 500mb height (or any other pressure level) it means that that is the height (in dekameters or meters) at which the air pressure reaches's the opposite of sea level pressure.

Did that help?

(Senior Storm Chaser)
Fri May 31 2002 04:52 PM
Re: Question for the Meteorologists out there...

Yeah it did, thanks.. That's kind of what I figured. I'd also assume that the lower the MB's the less air pressure - in that an 800mb pressure level is probably closer to the surface than say a 200mb which would signify less air pressure than the 850 or say the 1012 at the surface.

So my questions then are at approximately what height are the main mb indicators - 200, 300, 500, 700 and 850 and what does each specifiy. I thought the 200 was often used for upper wind speeds/flow, but that's the only one that I'm clued in on. I think some of the others might signify moisture at a certain level or whatever, but I'm not nearly as clear as I need to be in order to interpret stuff at the level I want to interpret it.

Thanks for any add'l info.


Note: This is NOT an official page. It is run by weather hobbyists and should not be used as a replacement for official sources. 
CFHC's main servers are currently located at in Orlando, FL.
Image Server Network thanks to Mike Potts and Amazon Web Services. If you have static file hosting space that allows dns aliasing contact us to help out! Some Maps Provided by:
Great thanks to all who donated and everyone who uses the site as well. Site designed for 800x600+ resolution
When in doubt, take the word of the National Hurricane Center