An analysis of the January 6-7, 2017 Winter Weather Event across north/central Georgia
Lara Pagano, National Weather Service (Atlanta, GA), Peachtree City, GA
Keith Stellman, National Weather Service (Atlanta, GA)
Steven Nelson, National Weather Service (Atlanta, GA)
David Nadler, National Weather Service (Atlanta, GA)
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Abstract
High impact weather events require a certain level of Decision Support Services (DSS) to ensure the protection of life and property.  At times decisions have to be made days in advance of the actual weather event.  Therefore, having high confidence of an event's occurrence is ideal. However, the complexity of any forecast will ultimately lend itself to uncertainties.  Even with a high degree of confidence, there is always a level of uncertainty that needs to be expressed as part of DSS. During a high impact winter event in 2017, NWS Atlanta was able to utilize experimental snowfall graphics to highlight forecast confidence and uncertainty.  Through a thorough analysis of this winter event we will highlight the challenges of expressing uncertainty while also reviewing the importance of communication with a rapidly evolving system. 

On January 6-7th, 2017, a high impact winter event crossed north and central Georgia.  Ahead of this system, NWS Atlanta supplied three experimental probabilistic snowfall graphics across the forecast area in an effort to illustrate the wide range of potential outcomes from this system; the minimum, most likely and maximum snowfall scenarios. These graphics proved useful as mid-level warming began to impact precipitation type across metro Atlanta during the event, eventually reducing snowfall totals.  Advertising the various snowfall solutions aided in effective communication of the large scale potential for model variability and forecaster uncertainty. While the snow did not materialize across most of metro Atlanta, the transition to sleet and freezing rain added another layer of complexity to this winter event. The changing impacts were quickly communicated to the core partners and public as the system continued to evolve. 

Through the use of probabilistic graphics, email briefings and webinars, NWS Atlanta was able to assist in the decision making process ahead of this event, while also providing frequent updates as the system evolved.