The weather professionals have been puffed up and posturing with graphs, maps and all their Doppler mechanisms for several weeks now trying to predict what the winter of 2015-16 will be like. Will there be blizzards like we’ve never seen? Will there be ice storms that shut down cities, airports and interstates? Or will it be a “quiet” winter with tempered temperatures and balmy afternoons?
One thing is for certain: people like to talk about the weather. But when they do, are they using consistent language and terminology? For instance, what does sleet mean to you, and how is it different from freezing rain?
The American Meteorological Society uses the Classification of Precipitation Types during Transitional Winter Weather Using the RUC Model and Polarimetric Radar Retrievals to apply some consistency and standards to weather terminology.
The classification algorithm they use distinguishes between nine classes of precipitation near the surface. The winter precipitation classes provided by this algorithm are:
- Dry snow
- Wet snow
- Ice pellets /sleet
- Freezing rain
- Freezing rain and ice pellets mix
- Heavy rain
Another unofficial term is graupel, which are snowflakes that have become encrusted with ice. This happens when snowflakes pass through a chilly cloud on their way down and water droplets freeze on them.
Where are snowflakes on this list?
Snowflakes are made of ice crystals. Impressively, each snowflake is made of as many as 200 ice crystals.
Just like in kindergarten when we all cut out our own snowflakes by folding paper and clipping triangles and circles out of the folds, snow crystals are symmetrical and they can form a hexagonal shape because that is how water molecules organize themselves as they freeze. Others are small and irregularly shaped. If they spin like tops as they fall to the ground, they may be perfectly symmetrical when they hit the Earth. But if they fall sideways, they will end up lopsided.
We have all heard that no two snowflakes are identical. This is because even though most have a hexagonal structure, there are so many ways that water molecules can arrange themselves as the water freezes, the options are endless. No two snowflakes have exactly the same arrangement of molecules, but they can look alike.
What combination of these and other factors are required to create a winter wonderland blizzard?
Three things are needed to make a blizzard:
- Cold air (below freezing) is needed to make snow.
- Moisture is needed to form clouds and precipitation.
- Warm, rising air is needed to form clouds and cause precipitation.
Even with this classification, there are events that can alter the expectations of a season. One of those is El Niño. El Niño is the periodic warming of water in the Pacific Ocean every few years. When it occurs, it means more energy is available for storms to form there.
Winters, during the El Niño effect, are warmer and drier than average in the Northwest, northern Midwest, and upper Northeast United States, so those regions experience reduced snowfalls. Meanwhile, significantly wetter winters are present in northwest Mexico and the southwest United States, including central and southern California, while both cooler and wetter than average winters in northeast Mexico and the Southeastern United States.
The El Niño of 2015-16 is the strongest El Niño in 50 years and this means locations across North American that do not typically see a white blanked Christmas holiday just might this year.
Either way, we hope your days will be merry and bright, even if your Christmas is not white.
Melody Smith, Blog Wrangler and Extreme Foodie