As meteorologists, there are many weather models available to us to help make our forecasts. The two most reliable models are the European and American models. Most meteorologists take these two models into significant consideration when looking at forecasts within a week. Occasionally, these two models battle with solutions, for a particular weather event, causing the end results to be quite opposite. One example is with Monday's forecast. 

A coastal low is expected to move up the East Coast bringing with it rain and clouds across much of the Northeast.  Both models have this general idea. However, the European model brings some rain from this system over our area Monday morning, while the American model has the rain well to our south and east.

  If you follow the American model, you would believe no rain on Monday, but if you follow the European model, you would believe rain on Monday. To take both solutions into consideration, we include rain our forecast for Monday, but at a low 30% or 40%. Therefore, rain is possible on Monday, but it is not likely until both models (and other models) agree are consistent with this idea.