Today I spotted an ominous cumulonimbus cloud rolling on top of Albany. With the temperature at nearly 40°F and some wet snow falling from the sky, I couldn’t help but wonder if I’d get to see the famous ‘thundersnow’ that meterologues get hyped about (if you want to see a Weather Channel guy go crazy with excitement over thundersnow, click here). Thundersnow, like its name suggests, is a thunderstorm that produces snow instead of rain. This is a very rare event because for thundersnow to happen, a winter storm needs convection, or upward moving air, which is very rare in winter. It’s a real treat for the science geek though. To quote Jim Cantore experiencing thundersnow in Boston, “You can have your $500 million jackpot in Powerball or whatever, but I’ll take this baby!”. Alas, the conditions were not right for my thundersnow, because instead I got hailed by graupel.
Graupel is a type of snow. It happens when snowflakes encounter supercooled water droplets, which stick to the snowflake and freeze instantly. So instead of ice, and instead of snow, you get little granular objects that look like opaque diamonds.
This is different than hail, which are raindrops that turn to ice as they are carried back upwards in a storm cloud, or sleet or ice pellets, which are also raindrops that turn to ice but are smaller than hail. Snow is formed without the liquid phase – it is water vapor that is directly transformed into ice crystals.
Graupel showers don’t seem to last for very long (about 5-10 minutes). Those ice balls pack a lot of moisture and since the ground temperature was well above freezing, a surprising amount of water showed up in a short period of time, running down streets or rooftops. Not a lot of people were seen out and about during the graupel shower (it’s like getting hit by miniature snowballs) and the only sign of life I saw was a child stomping her feet after the storm was over, complaining that it didn’t snow more. It was something I seconded –snow cover is extremely important to combatting global warming.
Snow is a crucial part of our biosphere. It helps regulate the temperature as a counterpart to the greenhouse effect (which is supposed to be beneficial to the planet, but is beginning to harm it thanks to humans adding CO2 and other pollutants in the atmosphere). It does this by reflecting the excess heat back to the atmosphere, since snow is white and absorbs very little sunlight. That’s why having snow on the ground in winter, that “blanket of white” that looks magical and inspires us, is so important to the planet. That is also why so many scientists fixate on the Arctic and Antarctica, where some degree of snow and ice cover is supposed to be permanent. The more “white areas” that the planet loses means the more we can expect the temperature to sky rocket.