The revised product will be made publicly available on this website in early May 2009.

Part 1 - Mission Connection

The Storm Prediction Center is the National Weather Service’s center of expertise for forecasting convection, including economically-disruptive weather events such as tornadoes, large hail, damaging winds and heavy rainfall. Included within the convective outlooks is a forecast for a 10% or greater probability of thunderstorms. Since these thunderstorm forecasts cover a 24 hour period with only the 10% probability contour, they provide little in the way of temporal or spatial resolution. Forecasts of thunderstorms are critical for the protection of life and property since every thunderstorm contains lightning that is a potential killer.

This Product Description Document replaces the existing PDD, whose evaluation period expired on 15 February 2008, and revises the current experimental SPC thunderstorm guidance product based on customer and partner feedback. The revision to be tested this year provides greater temporal detail to aid NWS aviation weather partners including NWS WFOs and to support time-sensitive decisions related to thunderstorms. This year’s test will also evaluate changes in the distribution of SPC forecaster workload and the ability to maintain this product for all scheduled convective outlook times.

The current enhanced resolution thunderstorm outlook was suspended on 27 February, 2009 to facilitate transition to the new experimental format. The SPC will again make the revised thunderstorm outlooks open to all customers through its web site at http://www.spc.noaa.gov/products/exper/enhtstm/. Web feedback from the broader community will be sought via an internet link beginning on 7 April 2009 and ending on 5 February 2010, at which time a decision to proceed with testing, revise the test or to continue on the path to operational production will be made. Internal NOAA evaluation will proceed the return to the public website which is scheduled for Tuesday 5 May 2009. Since the product will be in the public domain, this outlook can be repackaged and re-transmitted in accordance with standard NWS product use policies. Pending continued success, the SPC plans to distribute these probabilistic thunderstorm outlooks via AWIPS and the NDFD for use by both NWS WFOs and NOAA partners. An NWS Public Information Statement (PNS) Service Change Notice (SCN) will be issued prior to official operational product distribution.

Part II - Technical Description

Only a forecast for 0400 - 1200 UTC will be produced in conjunction with 0100 UTC Day 1 Convective Outlook.

The issuance and valid times of the new product will be:

 Issue Time         Valid Periods (UTC)

   0600Z      1600-2000, 2000-0000, 0000-0400
   1300Z      1600-2000, 2000-0000, 0000-0400
   1630Z      2000-0000, 0000-0400, 0400-1200
   2000Z      0000-0400, 0400-1200
   0100Z      0400-1200

Each of these forecasts will contain 10%, 40% and 70% contours for the probability of thunderstorms during the forecast period. Similar outlooks have been produced both internally and publicly by the SPC for three years and verification indicated these forecasts are skillful and statistically reliable. These thunderstorm hazard probabilities will provide SPC customers and partners with information to help provide better public safety for the United States public.