Initial Model

14.B Develop an initial model to explain how precipitation that is happening in one part of the country at one point in time could be connected (cause/effect) to what is predicted to happen in another part of the country at a later time. Use a previous model to identify mechanisms at the observable and the particle levels to explain the causes of this large-scale weather phenomenon.

• Identifying large areas of colder air and warmer air over the US at different points in time.
• Showing areas of colder and warmer air moving or changing in size over time.
• Explaining that something is causing those areas of air to move over time. Students may connect this to the movement of water vapor or clouds over time.

You may (or may not) see some students using these ideas and representations as well:

• Air masses are large parcels of air (hundreds of miles wide) with similar characteristics (e.g., temperature, humidity).
• There is an imaginary system boundary between where two air masses meet (a front).
• Low pressure systems and fronts are where air is rising; they tend to produce clouds and precipitation over and around them when there is enough water vapor in the air.

Collect Initial Model at the end of the class period. Make a copy of or photograph the students' initial models for future reference so you can assess individual student growth in this lesson set in explaining weather resulting from large-scale frontal interactions.