The process of evaluating the potential to name a storm begins with the daily hemispheric map briefing among the Global Forecast Center’s team of meteorologists at The Weather Channel.
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, and after a couple of years experimenting and refining different quantitative methods, the team developed and implemented a 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 and advisories.
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, Vt. The IMPACT method includes both actual (current or expired) National Weather Service warnings and advisories, as well as those that the naming committee anticipates are likely to be issued as the storm progresses. Only winter precipitation warnings and advisories are considered.
Figure 1: Graph of the 2012-13 named winter storms based on population and area that were under some sort of National Weather Service winter weather warning or advisory.
(MAP: Current Winter Alerts)
Thresholds have been established that must be exceeded before a storm will be named. To calibrate these thresholds, all 27 named storms from the 2012-13 season were re-evaluated based on the footprint of actual winter weather warnings and advisories 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, advisories and the combination of warnings and advisories 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 million) an 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
- Winter Weather Advisories: 8 million people or 600,000 square kilometers
- Winter Weather Advisories + Winter Storm Warnings: 10 million people or 1 million square kilometers
Based on these results, for 2013-2014, the general guidance for naming a winter storm is that either the areal or population thresholds must be met for each of the advisories, warnings and the combination thereof. 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.).
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, advisory and combined population thresholds easily and nearly exceeded all of the areal thresholds as well.
IMPACT map for Winter Storm Hercules which affected more than 50 million people and 300,000 square kilometers. Counties in purple were National Weather Service winter weather warnings and those in red were advisories. The storm is plotted on the right side of the figure to show its place within the warning guidelines for population and area.
STORM:CON Winter Impact Ratings
In addition to the IMPACT process to name winter storms, The Weather Channel also has developed a method to highlight the level of impacts that various locations could experience from winter storms. STORM:CON assigns an impact rating on a scale from 1 to 10 to give the user a sense for how impactful a winter storm is expected to be in their specific area. The scale follows a format similar to how the National Weather Service assesses impacts from freezing rain events. The STORM:CON scales are shown below:
- 10: Debilitating storm, major travel issues (Winter Storm Nemo, Winter Storm Atlas, Snomageddon - Feb. 2010)
- 8-9: Widespread road, school, business closures - Major winter storm warnings
- 6-7: Limited road, school, business closures – National Weather Service winter storm warning thresholds
- 4-5: Some disruption to road and air travel – National Weather Service winter weather advisory thresholds
- 1-3: Snow and Ice, but no significant impacts
The impact numbers are calculated based on the forecast database from the Global Forecast Center at The Weather Channel and is based on methods highlighted in research work for the Local Winter Storm Scale (LLWS) developed by Cerutti and Decker (2011). It incorporates several meteorological parameters including forecast snow and ice accumulation, wind speed and visibility.
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 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.
MORE: Photos From Winter Storm Hercules in Early January 2014
Hercules Satellite Image
This image taken on January 3, 2014 by the Suomi NPP satellite shows the blanket of snow that stretches from the Midwest across to New England after a massive winter storm moved over the region on January 1-3, 2014. (Source: NASA/NOAA)