Identify two important factors in collecting and analyzing weather data in the united states

One important factor is location - the reason being that the United states are a very big country and that you cannot surely measure the weather based on one location and from that deduce how the weather will change for all locations in the US. 

Another important factor is the models used in the analysis - one has to realize and know that such data sollections is limited by the analysis in terms of its accuracy, a certain forecast doesn't necessarily mean that it will also be absolutely correct. 

Density and pressure