Warn-on-Forecast Project

Phase 1: Capability Demonstration

Severe weather hazards, such as tornadoes, strong winds, large hail, and flash flooding cause tens to hundreds of fatalities and billions of dollars of property damage annually1, 2. These impacts could be mitigated with timely and actionable community-scale public messaging, but reliable issuance of watches/warnings at the community level with longer lead-time is very challenging because these hazards are often associated with rapidly developing, intensifying, and evolving thunderstorms.

The current NWS convective warning paradigm largely relies on trained-spotter reports and certain radar and satellite signatures, which constrains a longer lead time. To extend severe weather warning lead time and enhance/improve community centric warning services, the NWS plans to operationalize probabilistic quantitative forecast guidance available from a convection-resolving numerical weather prediction ensemble system. The target system is the Warn-on-Forecast System (WoFS) developed by the National Severe Storms Laboratory (NSSL).

WoFS is an end-to-end, on-demand system with one or more relocatable regional forecast domains running on a cloud-computing platform. The system is capable of providing reliable probabilistic forecast guidance for potentially dangerous severe weather hazards caused by individual thunderstorms, complexes of thunderstorms, and even overland impacts from tropical cyclones. Forecast guidance available from WoFS will help NWS forecasters to deliver advanced, precise, and actionable weather information to the communities they serve.

1Billion-Dollar Weather and Climate Disasters
2Weather Related Fatality and Injury Statistics

Extreme surface winds (color fill) and radar reflectivity (black contours) predicted by WoFS
WoFS-predicted location of favorable environment for significant tornadoes (color fill); observed storm objects (black fill)
Extreme rainfall rates predicted by WoFS

The Warn-on-Forecast System (WoFS) is an ensemble analysis and prediction system running over 900 km x 900 km relocatable forecast domains at 3-km grid spacing. Graphical probabilistic forecast guidance for various environmental and storm-scale variables is produced at 5-minute intervals for up to 6 hours, providing valuable information about the likelihood of various scenarios associated with rapidly evolving storms and weather hazards.

Overlay capability of radar observations, local storm reports, and warning polygons aid warning decision making and quasi-real time verification with WoFS. The capability has been demonstrated experimentally since 2017, growing from use at the NWS Weather Forecast Office (WFO) and Storm Prediction Center in Norman, Oklahoma, to annual demonstrations in the NOAA Hazardous Weather Testbed and real-time use and evaluation at other national centers and dozens of WFOs across the country.

The NWS, working with NSSL, plans to continue and expand the WoFS demonstration capability in 2025. During the 2025-2026 demonstration period, comprehensive requirements for transitioning to operations will be developed and documented, and the system will be applied to provide real-time experimental probabilistic guidance where it is currently lacking - between the severe-weather watch and warning time scales.

Demonstration Timeline

  • February 2025: Develop initial demonstration protocol
  • March 2025: Initial NWS demonstration capability
  • April 2025-September 2026: Provide real-time WoFS guidance as requested
  • May 2025: Participate in HWT SFE
  • June 2025-September 2026: Explore additional use cases across a wider range
  • September 2026: Complete Concept of Operations

Graphics courtesy of the National Severe Storms Laboratory.