Hpa For A Newbie

[davyf]

Hi all, I'm still brand new to the site and am still trying to get my head round just about everything on here. Something that has got me really confused is the use of hpa.

I understand that hpa (hectopascal) is a measure of air pressure and hope I'm right in thinking that this pressure decreases the further up you go in the atmosphere and the air becomes thinner. So am I right in thinking that the 1000hpa wind vectors I see on the chart are low level winds when compared with the 300hpa wind vectors? The 300hpa vectors are a lot more uniform on the charts and so does this mean the winds high up in the atmosphere are a lot more settled (I always assumed it was a lot more turbulent up there).

Also, in laymans terms, how do you use these wind vectors? If I see, as at the moment, a big bank of snow, how do I know whether it is following the course of the 300hpa vetors or the 1000hpa vectors. I know this is probably a question that will have so many other variables attached to it but just a rough idea would be much appreciated.

[dave48]

Not an expert i'm afraid but until one of them has time to do a full answer for you, here's a basic one.

You're correct in thinking the 1000hpa is at the bottom around the surface and the 300 hpa is higher up, it decreases with height put simply. So yes the winds correspond to this.

Indeed the wind vectors higher up are more 'uniform', someone more knowledgable could explain why that is to you. However height doesn't mean strength or turbulence, two very different things, quite simply winds can vary at different heights and with regard to their strength they will be very strong aloft if you have a jet stream over running your area of interest, if not then they won't be as strong.

With regard to using wind vectors it depends on the height of the clouds but is fairly complex yes, but put simply if the clouds are quite low based, they are probably moving with the lower vectors. The best way to check is to run a radar loop and then you can get an idea which way the clouds you are interested in are moving.

Hope that quick reply helps and someone can expand on the complexities for you if they have time.