An Introduction to Upper Air Charts

Updated August 3, 2015

One of the first things you'll likely learn in meteorology is that the troposphere -- the lowest layer of Earth's atmosphere -- is where our day-to-day weather happens. So in order for meteorologists to forecast our weather, they must closely monitor all parts of the troposphere, from bottom (the Earth's surface) to top. They do this by reading upper air weather charts -- weather maps that tell how weather is behaving high up in the atmosphere.

There are 5 pressure levels that meteorologists monitor most frequently: the surface, 850 mb, 700 mb, 500 mb, and 300 mb (or 200 mb). Each is named for the average air pressure found there, and each tells forecasters about a different weather condition.

1000 mb (Surface Analysis)

Surface weather map showing Z time. NOAA NWS NCEP

Height: Approximately 300 ft (100 m) above ground-level

Monitoring the 1000 millibar level is important because it lets forecasters know what the near-surface weather conditions are we're feeling right where we live.

1000 mb charts generally show high and low pressure areas, isobars, and weather fronts. Some also include observations like temperature, dewpoint, wind direction, and wind speed.

850 mb

NOAA NWS NCEP

Height: Approximately 5,000 ft (1,500 m)

The 850 millibar chart is used to locate low-level jet streams, temperature advection, and convergence. It's also useful in locating severe weather (it's typically located along and to the left of the 850 mb jet stream).

The 850 mb chart depicts temperatures (red and blue isotherms in °C) and wind barbs (in m/s).

700 mb

A 30-hour forecast chart of 700 milibar relative humidity (moisture) and geopotential height, produced from the GFS atmospheric model. NOAA NWS

Height: Approximately 10,000 ft (3,000 m)

The 700 millibar chart gives meteorologists an idea of how much moisture (or dry air) the atmosphere holds.

It's chart depicts relative humidity (green color-filled contours at less than 70%, 70%, and 90+% humidity) and winds (in m/s).

500 mb

NOAA NWS NCEP

Height: Approximately 18,000 ft (5,000 m)

Forecasters use the 500 millibar chart to locate troughs and ridges, which are the upper air counterparts of surface cyclones (lows) and anticyclones (highs).

The 500 mb chart shows absolute vorticity (pockets of yellow, orange, red, and brown color-filled contours at intervals of 4) and winds (in m/s). X's represent regions where vorticity is at a maximum, while N's represent vorticity minimums.

300 mb

NOAA NWS NCEP

Height: Approximately 30,000 ft (9,000 m)

The 300 millibar chart is used to locate the jet stream's position. This is key to forecasting where weather systems will travel, and also whether or not they'll undergo any strengthening (cyclogenesis).

The 300 mb chart depicts isotachs (blue color-filled contours at intervals of 10 knots) and winds (in m/s).