One of the issues we commonly see each winter is that there are many sub-criteria events that don't prompt watches, warnings or advisories, yet have a high impact to the public in terms of deaths, injuries and property damage from road ice-triggered accidents. Light sub-criteria freezing rain can cause events such as the February 23, 2011 accident outbreak in St. Louis, a high-impact outbreak that occured completely without warning due to the precipitation amounts being below established criteria. Likewise, light snow can also cause such a high-casualty event like we saw across the Midwest region this past Thursday and Friday, which has claimed at least 5 lives and hundreds if not thousands of vehicle damage incidents across several states. Here are a few news articles:
Light snow creates icing that is deceptively innocuous-appearing, particularly in high-traffic areas where the white coating is compacted into 'black ice' in the center of the road. Furthermore, these events typically recieve little media coverage and consequent low public awareness levels. As a result, vehicles are typically traveling - and crashing - at much higher speeds during light snow events than they do during big snowstorms. Many of the mass-casualty icing events I have tracked in past years have been due to light amounts of either snow or freezing rain. Most of those were too light to trigger watches, warnings or advisories, and those that barely crossed that threshold only received a lightly-worded advisory.
The National Weather Service currently issues products directly concerned with road icing, but they have two main problems:
The products are not directly named for the hazard. Winter Weather Advisories, Freezing Rain Advisories, Freezing Fog Advisories and Snow Advisories are all products that are issued solely to cover the road ice hazard. The conditions prompting these products pose no other threats to the public than hazardous motor vehicle travel (and to a lesser extent a walking hazard). The more meteorologically-educated person will immedialy recognize each of these products and their implications with little thought, but the non-weather-saavy person usually will not. Re-titling these as "Road Ice Warning" or something similar would convey the hazard more plainly to the end users (public and media). If the importance of naming the precipitation type responsible remains a necessity, then possibly the ptype could be appended to the warning title "Road Ice Warning for snow"; "Road Ice Warning for freezing rain". Removing the need for the end user to make a mental connection between the name of the advisory and its hazard would certainly improve the overall communication of what the real danger is.
It's true that the supporting text of these advisories mentions hazardous travel, but it is unusual for members of the general public to hear or read this additional text. The title of the product is the most important, as it usually receives widespread broadcast via television, radio, digital highway signs, social media, text message, email alerts, web sites and more.
The precipitation amount criteria for these products is too high. Compounding the problem of the current suite of products is that while they are solely concerned with road icing, they are often not issued for light sub-criteria events that have the same public impact as advisory-critera events. This is evident in the many such events we see each winter, such as 2/23/11 in St. Louis and 12/8-9/11 from Nebraska to Indiana.
The cost and manpower needed to make these simple changes will be minimal if not non-existent. Here's why:
High-impact icing events occur infrequently. Lowering the precipitation amount criteria will result in more "Road Ice Warnings" being issued than the current suite of advisories see, but only by a factor of two or possibly three in most areas of the US. Not nearly enough to begin to place an undue burden on the system and personnel, nor enough to create a 'crying wolf' syndrome. The highest icing-related death rates occur in a belt traversing the Midwestern USA, places in which roads are normally ice-free except for a dozen or so discrete events each winter. Currently only a half or so of those trigger advisories or warnings, yet all have the same level of public impact potential.
High-impact icing events are easy to detect in advance. While many light icing events are not evident in models more than 12 hours out, when they are imminent (less than an hour or two away), they are easy to spot. Most of the time these involve rain showers or snow bands moving toward (or developing over) ASOS/AWOS stations reporting below-freezing temperatures - nearly all of which are evident early enough to get warnings out to the public. Most NWS forecasters are already keenly aware of the potential for such events, but lack the authority and protocol to "sound an alarm" via a strongly-worded, universally-understood warning once it appears likely to happen. This has been the case with many events we've seen each winter.
Will a "Road Ice Warning" solve the problem and prevent all accidents and resultant deaths and injuries? Of course not. Tornado warnings don't prevent all tornado deaths, yet they have proven indispensable and effective for the members of the public who will follow them. Likewise, there's no reason to expect that a similarly-aware member of the public wouldn't take heed to a warning for road ice. The low cost and simplicity of implementing a Road Ice Warning product, combined with its potential for saving lives, makes it a priority that I hope our officials will strongly consider soon.