High air pressure in high mountains areas
I have been looking recently at the air pressure map and noticed that during the last few days, some high mountains areas have been displaying relatively high air pressure.
I am a total amateur so I might be saying something inaccurate, but I thought that air pressure was supposed to get lower when getting at higher altitudes.
Is there a reason why this occurs ?
Here are some screenshots for the Himalayas, the Andes and the New Guinea Highlands :
Looking forward to read your answers.
vsinceac last edited by vsinceac
These are not like values measured by barometers of surface stations; instead, they are barometric measures reduced to mean-sea level pressure, see info provided for this parameter in scereenshot.
Atmospheric pressure on big mountains may be something like 550 hPa, thus Windy Pressure data layers show all MSL (mean sea level) values.
You are right, in mountains the air pressure actually decreases with altitude. But in Windy, the Pressure layer shows the air pressure corrected to sea level (mslp).
We could therefore expect to see on a mountain range the same relative pressure as in the surrounding region. In fact we observe often a higher pressure (mslp) above mountain ranges. At high level there are fairly high winds due to synoptic weather conditions or to prevailing winds. In Windy, you may see them for example at 500hPa level (about 5500m) over these mountainous region. The air flow which then passes over the mountain range is somewhat squeezed and compressed by the high relief, which results in a higher local air pressure.
Thank you for your answers !
Indeed this makes more sense, I was still not very familiar with the Mean Sea Level Pressure concept.
I found an interesting definition on the US National Weather Service website that mentions these anomalies :
MEAN SEA LEVEL PRESSURE: This is the pressure reading most commonly used by meteorologists to track weather systems at the surface. Like altimeter setting, it is a "reduced" pressure which uses observed conditions rather than "standard" conditions to remove the effects of elevation from pressure readings. This reduction estimates the pressure that would exist at sea level at a point directly below the station using a temperature profile based on temperatures that actually exist at the station. In practice the temperature used in the reduction is a mean temperature for the preceding twelve hours. Mean sea level pressure should be used with caution at high elevations as temperatures can have a very profound effect on the reduced pressures, sometimes giving rise to fictitious pressure patterns and anomalous mean sea level pressure values.