White lines + values = mean sea level pressure isobars each 5 hPa (hectopascal).
Grey dashed lines + values = temperature at 500 hPa.
Colored zone = height contour 500 hPa each 4 gpdam
H = high pressure.
T = low pressure. 

Useful for: trough & ridge pattern propagation (long waves) and short waves, steering pattern of frontal systems, detect cold and warm air masses, and estimate stability of atmosphere (stable with warm upper air, unstable with cold upper air).