NWS Efforts to Improve Forecasting and Messaging of Uncertainty

The United States endured another brutal and active winter in 2014-2015. One of the most noteworthy storms of the season was a crippling Nor'easter that impacted the northeastern corridor between January 26-28, 2015, producing snowfall accumulations of one to three feet and blizzard conditions from Long Island to New England. The storm was preceded by widespread publicity with forecasts of a “potentially historic” snow storm for the Northeast. Severe conditions were expected in large cities, such as New York City (NYC), Boston and Philadelphia. The forecasts and warnings prompted major preparations leading up to the event, where major infrastructure elements, including the NYC subway, were shut down. While the forecasts were largely accurate, particularly in Long Island and New England, a shift in the expected storm track by 50 to 100 miles to the east resulted in eastern Pennsylvania, New Jersey and southeastern New York receiving far less snow than expected. The over-forecasted snow amounts for Philadelphia and NYC generated some criticism, upstaging the excellent, pre-emptive decision making that saved lives and further economic disruptions from NYC to New England.

This event illustrates the challenges the National Weather Service (NWS) faces in effectively assessing and communicating forecast uncertainty. This presentation will focus on the lessons-learned from the January 2015 Nor'easter and efforts already underway to better convey forecast uncertainty. For instance, this storm was the first large-scale event to occur under the expanded use of experimental, probabilistic snowfall graphics at select NWS forecast offices in NWS Eastern Region, including the offices that cover Boston, NYC and Philadelphia. This presentation will review these graphics and other means NWS used to express forecast confidence in advance of this event. Feedback from the NWS partners and the public will also be discussed.

The presentation will also provide an update on new initiatives within NWS that could lead to improvements in the communication of forecaster confidence. Key among these initiatives is the NWS Hazards Simplification (“Haz Simp”) Project. The goal of Haz Simp is to consider alternatives to the current NWS "Watch, Warning and Advisory" (WWA) system. Motivation for this project is based on feedback indicating that the use of multiple WWA products, especially during complex events such as the multiple storms across the country this past winter, sometimes results in confusion among users.

A possible remedy for this confusion is to consider evolving towards a system that replaces the current, criteria-based "yes/no" WWA system towards a system that communicates impacts, severity, timing and certainty in a hierarchical and continuous manner. The Haz Simp project plan, which will include multiple opportunities for feedback among all stakeholders of the WWA system, will also be discussed. The timing of these opportunities will be discussed as part of the presentation.