Instructions: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: A weather map is an important tool for geographers.   A succession of three or four maps presents continuous picture of weather changes. Weather forecasters are able to determine the speed of air masses and fronts   to determine whether an individual pressure aroa is deepening or becoming shallow and whether a front is increasing or decreasing in intensity  .They are also able to determine whether an air mass is retaining its original characteristics or taking on those of the surface over which it is moving. Thus, a most significant function of the map is to reveal a summary picture of conditions in the atmosphere at a given time. All students of geography should be able to interpret a weather map accurately.Weather maps contain an enormous amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States  Weather Bureau issues information about approaching storms, floods, frosts and all climatic conditions in general. Twice a month it issues a 30-day"outlook" which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an anaiysis of the upper air levels which often set the stage for development of air masses, fronts and storms. Considerable effort is being exerted today to achieve more accurate weather predictions, with identifying and tracking storms over regions which have but few meteorological  stations. Extensive experiments are also in progress for weathef modification studies. 
 Answer: frosts
Output:
One characteristic of weather maps NOT mentioned by the author in this passage is  _  .