As mentioned in the ForeFlight blog back in June, the familiar prog charts pilots use every day will be changing. Hopefully you’ve had a chance to test drive these new NDFD prog charts that were introduced in ForeFlight Mobile 7.1. Beginning this morning (September 1, 2015) the precipitation forecast on these charts will now originate from meteorologists at the local NWS forecast offices and not from meteorologists at the Weather Prediction Center (WPC). For more information, you can read the official NWS notification.
Still a forecast for precipitation coverage
The precipitation shown on the new chart represents an instantaneous precipitation forecast. That is, it shows expected likelihood and coverage of precipitation (including type) at the valid time on the chart. Essentially the light shaded areas define at least a 15% chance and dark shaded areas define a 55% or greater chance of precipitation reaching the surface in that period. A legend in the lower-left corner designates the likelihood of precipitation (chance versus likely) as well as the precipitation type (snow, rain, mix, thunder, etc.). Nevertheless, the isobaric forecast along with high and low pressure centers and a forecast for the position of surface fronts will continue to be issued by the same meteorologists at the WPC.
For better or for worse?
It goes without saying that not every change is necessarily an improvement. It’s not that the other precipitation forecasts were bad; however, given that the precipitation forecast on this new chart is generated by meteorologists at the local forecast offices, it will be more consistent with the terminal forecasts (TAFs) and the local weather forecasts from weather.gov since the TAFs and local weather forecasts are issued by those same local meteorologists. Perhaps the biggest drawback of the new imagery is that the precipitation forecast now ends at the U.S. border although the isobaric forecast and forecast for surface fronts will still cross over into Canada, Mexico and coastal waters.
Here’s what we did in ForeFlight
Given that the legacy prog charts are no longer issued, we’ve moved the new prog charts from their initial home under the NDFD Progs collection to the Prog Charts collection where they will replace their legacy counterparts. Note that the extended forecast progs (Day 3 through Day 7) located in the Prog Charts collection will not be affected.