There are a few different ways to look at snowfall accumulation forecasts. The most common way is through the snow accumulation map as shown below.
That gives you a general idea of our thinking, but the forecast is not always that cut and dried. We like to use probability graphics for narrowing down the forecast and letting you know our confidence level and which direction we think it is more likely bust – but, hopefully it does not! The graphics below were sent to our Winter Forecasting Service for private clients earlier today to help them best prepare for the storm.
For this particular system these graphics are valid for the Providence Metro Area, Southern RI, and Bristol/Plymouth Counties in MA.
The following graphic shows how likely we think it is that the final snowfall total reaches the amount shown on horizontal access. You can see that we’re very confident in at least an inch of snow, but we become less confident in the potential for 3″ of snow. Also, based on the slope of the line, the door is still slightly ajar for a 4-6″ snowfall, but we think the odds of that occurring are very low.
The following graphic shows the odds that the final total is within one inch of the amount indicated along the horizontal axis. Basically, you’re looking for the peak of the hump to find where we think it is most likely the final total will be. In this case, the hump peaks at 2″, then slopes down to close to 0% after 6″. Notice how we also think it is highly unlikely that there will be less than 1″ of snow.