Measuring Pressure at the surface - reducing pressure to sea level

• A: We can reduce the pressure measurements to sea level using the following rule:

• in the lower part of the atmosphere, pressure changes by about 10 mb for every 100 meters of elevation change....

• Using this rule, we reduce all pressure measurements to sea level, producing a constant elevation sea-level pressure (SLP) chart ..., commonly referred to as a surface weather map

• Q: How is pressure represented above the surface????

QUESTION FOR THOUGHT:

1.  Pilots often use the expression "high to low, look out below." In terms of upper-level temperature and pressure, explain what this can mean?