The Science Behind Naming Winter Storms at The Weather Channel
By Tom Niziol
Published: November 18, 2014
The process of evaluating the potential to name a storm is a continual process that includes a daily hemispheric map briefing among the Global Forecast Center’s team of meteorologists at The Weather Channel.
(MORE: Why The Weather Channel Names Winter Storms)
During the map briefing, candidate weather systems are identified as potential winter storms up to a week out. As the certainty for an impactful storm increases, a storm naming committee schedules a conference call to discuss the potential named storm.
The committee is composed of three members: Tom Niziol, winter weather expert; Stu Ostro, senior meteorologist and senior director for Weather Communications; and Dr. Peter Neilley, senior vice president of Global Forecasting Services for The Weather Channel. Based on a thorough discussion of meteorological and societal factors that could produce a winter storm, a decision is made to name or not name. It is important to note that the decision to name a storm is solely held by this committee of meteorologists.
IMPACT Winter Storm Naming Tool Implemented in 2013-14
For the 2013-14 winter season, after the first season of refining objective methods, the team developed and implemented a quantitative procedure to evaluate the potential impacts of winter storms. The process, referred to as IMPACT for Integrated Meteorological Population and Area Calculation Tool, calculates the population and area that is forecast to be impacted by winter weather based on thresholds set by the National Weather Service for winter weather warnings.
The National Weather Service products have a proven track record and impacts are adjusted locally to account for the part of the nation being impacted by winter weather. So, as an example, a winter storm warning is issued for Atlanta when 2 inches of snow is expected in 24 hours, but it takes 9 inches to trigger a winter storm warning in Burlington, Vermont. The IMPACT method includes both actual (current or expired) National Weather Service warnings, as well as those that the naming committee anticipates are likely to be issued as the storm progresses. Only winter precipitation warnings are considered.
(MAP: Current Winter Alerts)
Thresholds have been established and there must be reasonably high confidence that those thresholds will be exceeded before a storm is named. To calibrate these thresholds, winter storms from the 2012-13 season were re-evaluated based on the footprint of actual winter weather warnings that were issued by the National Weather Service in association with each storm. Those storms were then plotted to choose a representative population and area that could trigger naming a winter storm (Figure 1).
Based on the plot of named winter storms, a base population and area thresholds were defined for warnings to separate the more significant named storms from other events. Those thresholds are used as a strong guideline to quantify the naming process.
In the image at the top right, the red lines show the chosen warning thresholds for population (2,000,000) and area (400,000 square kilometers, or 248,548 square miles). You can see that all storms from the 2012-13 season exceed the threshold for either population or area impacts, and most exceed both.
Guidelines for Naming Consideration:
- Winter Storm Warnings: 2 million people or 400,000 square kilometers
Based on these results, for 2014-2015, the general guidance for naming a winter storm was that either the areal or population thresholds must be met for warnings. While these guidelines are considered fairly strict, the storm naming committee still reserves the right to override the quantitative decision in certain circumstances. Some of the factors that may influence decisions to override the naming rules include the degree of historical significance of the event (e.g. accumulating snow in South Florida, a summer season snowstorm, etc.).
One exception is lake-effect snowstorms. The Weather Channel is currently not naming lake-effect snowstorms even if they meet the above criteria.
The IMPACT process brings a more quantitative approach to assessing impacts from winter storms. Below is an example from Winter Storm Hercules, which produced a wide swath of winter conditions from the Central Plains through the Northeast. Over the history of this storm, more than 50 million people covering an area over 300,000 square kilometers were impacted by winter weather. The storm exceeded the warning and population thresholds.
Winter Storm Naming Process Improvements Ongoing
The Weather Channel continues to explore opportunities to improve the assessment of winter storm impacts through other quantitative processes. For example, The Weather Channel has developed a version of a Regional Snowfall Index based on the National Climatic Data Center’s (NCDC) Regional Snowfall Index (RSI). Although the process only considers snowfall amount, it is adjusted through eight different climatological zones across the U.S. for population and areal coverage. The system is being tested again this winter and if it proves valuable in improving the process to name winter storms it may be used to augment the winter storm naming process in the future.
The meteorological team at The Weather Channel will continue to work to improve efforts to assess winter weather with the latest scientific methods to quantify the potential impacts from winter storms. Our goal is to provide the most up-to-date information to keep our users informed and prepared to handle whatever Mother Nature has to offer.