Twelve years of developmental data from 2000-2011 were used to derive the predictive equations using North American Regional Reanalysis (NARR) and lightning data. The PPF system uses the GFS gridded input data and provides probabilistic forecasts from 0 to 180 hours (7.5 days) in 3 hourly increments. The methodology used to derive the new PPF equations was similar to the NAM-based perfect prog forecasts that have been available since 2006.
The web page (www.spc.noaa.gov/exper/dryt/) will update after each of the (4) GFS cycles have been processed. The CONUS forecasts are available about 6 hours after each cycle time, while the Alaska forecasts are available about 7 hours after each cycle time.
The initial version of the web page includes the following graphics:
To avoid over-forecasting dry thunderstorms over the CONUS, the lower tropospheric humidity must be no higher than 50% for dry thunderstorms to be forecast. However, no humidity criterion is used for the dry thunderstorm equations in Alaska.
Experience during the final testing of these fields, using cases from the summer of 2013, have generally confirmed that dry thunderstorms are more likely to occur where:
For more details about the PPF methodology, see the Power Point or PDF Slides.
Comments and questions about the web page can be sent to: Patrick Marsh. Comments and questions about the display fields can be sent to: Phillip Bothwell.