Purpose: Outside of the probability of precipitation (PoP), forecasts supplied by the National Weather Service are entirely deterministic. Research shows that customers desire knowing the level of certainty/uncertainty in the forecast (Morss et al. 2008). The only method in which the NWS habitually provides such information is the Area Forecast Discussion (AFD).
The AFD is an open-format narrative written by the NWS forecaster when issuing a forecast and is "a means to explain the scientific rationale behind a forecast" (NWSI 10-503).
Often this includes some mention of the level of certainty in the forecast, though that information is usually obtained by the reader by getting an overall sense of the forecaster's sentiment, it is not explicitly stated. To provide certainty information in the shortest, easiest, and least obtrusive way, this project will ask NWS forecasters to explicitly state the level of certainty in the seven day forecast as a whole in a special section of the AFD (see example below). Certainty will be expressed for two separate periods (Days 1-2 and Days 3-7) and three levels (low, medium, high).

 

Verification: Two methods of verification will be utilized. The first will be based on solicited customer feedback and focused on the usefulness of the information. The second method will pair the certainty information with internal forecast verification statistics to determine if maximum temperature, minimum temperature, and PoP verified differently with varying levels of certainty. Additional verification aspects may be explored.

 

Click Here to View the Current AFD

 

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References:
Morss, R. E., J. L. Demuth, and J. K. Lazo, 2008: Communicating Uncertainty in Weather Forecasts: A Survey of the U.S. Public. Wea. Forecasting, 23, 974-991.

National Weather Service Instruction (NWSI) 10-503, 2012.