The 850 mb pressure surface, like the 500 mb pressure surface, is a “mandatory” level; this means that all radiosonde or upper air instruments record winds, temperature, and humidity precisely at 850 mb.

What is the 850mb chart used for?

In high elevations areas such as the High Plains and Mountainous West, the 850 mb level will be near the surface or even below the surface. The 850 mb chart is used as a proxy for the surface chart at high elevation areas while the 700 mb chart is used as a proxy for the 850 mb chart.

How do you read 850 mb chart?

THE 850 MB CHART. For locations close to sea level, the 850 mb chart represents the top (or close to the top) of the planetary boundary layer. In the PBL, friction and turbulent motion eddies are common. The wind blows at a more constant speed and direction above the 850 mb level.