top of page

EZTip No. 1 - Convective precipitation markers in EZWxBrief

During the warm season when viewing the EZMap in the EZWxBrief progressive web app you may have noticed several different types of precipitation markers that are rendered when the Weather depiction layer is selected like those shown below. To overlay these on the map, click or tap the layer selector button in the upper left and then expand the Station Markers layer and you'll find the Weather layer is the last possible item in the Station Markers list. These icons are also rendered at the top of the EZRoute Profile and EZAirport Meteogram. Let's go through each of these different icons.

For this weather layer EZWxBrief uses what is called the Precipitation Potential Index (PPI). The PPI supports the generation of National Digital Forecast Database (NDFD) 12-hour Probability of Precipitation (PoP12) forecasts and the categorical information provided by the NDFD weather grids used to generate the precipitation forecast on the Weather Prediction Center (WPC) short range prog charts. So what you see above should generally match the short-range prog chart forecast at the valid time of that forecast.


PPI values range from 0 to 100 and resemble PoP12 values in magnitude. The PoP12 for any 12-hour period can be derived by taking the maximum PPI value within the desired period. Please note that PPI is not a calibrated probability forecast, which has different statistical characteristics. For example, as temporal resolution increases probability should decrease. In other words, a 12-hour PoP forecast will have an equal or larger magnitude than a 6-hour PoP forecast. As temporal resolution increases, the magnitude of PPI remains unaffected. Below is a table showing how the PPI for both precipitation and convection is categorized.