White lines + values = height contours at 850 hPa, each 4 gpdam.
Black lines + values = temperatures at 850 hPa each 5°C
Colored zones = temperatures at 850 hPa each 2°C

Useful for: get an idea of the surface conditions like positions of surface lows and highs, location of cold and warm air masses, location of fronts, forecasting temperatures (warm advection = higher values, cold advection = lower values) and forecasting precipitation type.