To do it, you need to find the cloud height in feet above mean sea level (MSL). That's as simple as adding the elevation of the reporting station to the reported cloud heights. Once you know the cloud heights in MSL, you can determine where you should fly, since altimeters are set in feet above MSL, not in feet AGL. Example: At Grand Forks International Airport (KGFK), clouds are reported broken at 7,000 feet AGL. Add the reported clouds of 7,000 feet AGL to the field elevation of 845 feet MSL to get a cloud base altitude of 7,845 feet MSL. Surface observations, no matter how advanced the system, have limitations. They're limited by location and time, so they only really apply to an airport's immediate area.
Supremacy Clause. Article VI, Paragraph 2 of the Constitution is commonly referred to as the Supremacy Clause. It establishes that the federal constitution, and federal law generally, take precedence over state laws, and even state constitutions. See Preemption;constitutional clauses.
In 1920, the Supreme Court applied the Supremacy Clause to international treaties, holding in the case of Missouri v. Holland, 252 U.S. 416, that the Federal government's ability to make treaties is supreme over any state concerns that such treaties might abrogate states' rights arising under the Tenth Amendment.