Everyone is accustomed to the naming of hurricanes by the National Hurricane Center.
A few years ago, The Weather Channel thought it would be a good idea to name winter storms. It was an interesting concept, but it turns out that the difference between tropical cyclones and winter weather in the mid-latitudes is too great to make comparisons meaningful.
And now The Weather Channel has stretched the meaning of ‘winter storm’ to the point where the whole process is broken.
The Weather Channel should abandon what once seemed a useful effort and join The National Weather Service and other organizations in recognizing that ‘winter storm’ is a meaningless, often oxymoronic, term.
Or join Decoded Science in using helpful designations for weather events based on their individual characteristics.
Why We Can Name Tropical Cyclones
A tropical cyclone forms from the bottom up and is warm at all levels. It starts with a wave in the surface easterlies which circumnavigate the globe in the tropics.
Over water, an easterly wave has the capacity to convert heat locked up in water molecules that have been converted to water vapor into wind. Here’s how it works:
- A certain number of ocean water molecules evaporate into the air; this is accomplished by addition of heat, either from the air, the sun, or the water itself. The energy used to rip the water molecules from the ocean is locked in the water vapor molecules until they condense. The release of this energy upon condensation can be turned into kinetic energy of wind.
- The surface wave can build to higher levels of the atmosphere. The entire center of the storm is warm, heated by the energy released upon condensation of the water vapor molecules. At high levels, the warm core produces a high pressure center around which air spirals outward.
- The outward evacuation from the center of the storm at upper levels causes the pressure to drop at the surface and, since wind is proportional to the pressure gradient (change of pressure with distance), the wind increases.
The formation of a tropical cyclone is straightforward, and always leads to an identifiable low pressure center that deepens as the storm strengthens. The various stages of a tropical cyclone are precisely defined by the wind speed.
Extra-Tropical Cyclones Form From The Top Down
While tropical cyclones originate from easterly waves near the surface and work their way upward, extra-tropical systems begin as waves moving from west to east at jet stream level and work their way to the surface.
This is a simplification; the whole story involves complicated interactions at all levels of the atmosphere. But without waves in the jet stream there would be no weather in the mid-latitudes.
Where tropical cyclones are fueled by latent heat (energy locked in water vapor and released upon condensation), non-tropical systems are fueled by potential energy. When cold polar air moves south and warm tropical air moves north, they meet in a band of high potential energy — the lowest potential energy state has warm air on top of cold.
The release of this potential energy can result in wind, snow, freezing rain, and flooding rains. Significantly, there is no single criterion on which to base the naming of a ‘winter storm.’
The Weather Channel’s Cara Kerfluffle
The Weather Channel recently named “Winter Storm Cara.” Cara is a good example of why extra-tropical systems should not be named winter storms:
- The storm occurred in November, which is not winter by any definition. A ‘winter-type’ storm can occur at this time of year, but Cara was not even winter-type, considering that the majority of precipitation fell as rain.
- There was no identifiable surface low pressure center of any significance. Frequently winter weather systems have elongated low pressure, very weak low pressure, or multiple centers of low pressure (Cara had all three). But the upper air pattern always has the identifiable feature of a trough (dip) in the jet stream.
- The various types of precipitation form in a variety of ways.
To be sure, the weather system that The Weather Channel named Cara was significant. If it weren’t for the outsized importance of the freezing rain part of the system (at least six traffic fatalities were blamed on icy roads), Decoded Science would have named the entire system rather than just the freezing rain portion.
We would have noted the record warm temperatures associated with it as well as the flooding rains. These are not winter-like characteristics and the system should never have been called a winter storm. In fact, The Weather Channel itself referred to Cara as a ‘weather system,’ which is at least a little more accurate but no more informative.
The Bottom Line: Weather In The Mid-Latitudes Is Complicated
To call every instance of bad weather from fall to spring a winter storm is at best a well-intentioned but misguided effort at communication, at worst a disingenuous and misleading publicity stunt. Each situation that could produce noteworthy or significant weather should be handled on an individual basis. With the name Coldilocks for the recent (actually ongoing as of this writing) weather phenomenon, Decoded Science has initiated a system of naming weather patterns or events in an informative way.
OK, ‘Coldilocks and the Three Brrrs’ was whimsical, but it does communicate that only ‘just right’ conditions can produce freezing rain. What information does the name ‘Cara’ communicate?
The Weather Channel seems to be continually struggling to force mid-latitude weather to comply with its misguided analogy to tropical cyclones.
In the end, the public just wants to be informed about how the weather is going to affect the commute to work or the conditions at the Big Game. A name is of no value if it conveys no information.
Decoding Science. One article at a time.