Ice crystal formation

Sooner than we would like it to be, winter is approaching quite quickly. We have already seen the first frosts and freezes. We have seen wild storm systems move through with heavy rain, high winds, severe weather, and basically any type of weather you can think of (except of course snow). Soon, it will begin to become much colder, and we will soon be thinking of the holidays, and of course snow. If you recall my winter forecast, I specifically stated that I expect this winter season to be much more exciting than last year... What this means is that I expect more storms, more snow, and more cold weather. This article and the next one will primarily be about cloud formation, the crystals that make up the ice crystals, and what causes them to form.
   Before a cloud can form, two primary conditions must be in place that influence the development of the cloud. The first condition is primarily "lift". When I say "lift", what I mean is the literal lifting of air vertically in the atmosphere. Due to the laws of thermodynamics, this body of air must cool. This leads to the second condition, which is moisture. Without moisture clouds cannot form. A body of air will always have a specific amount of moisture. As it moves up, this value changes little (except when it changes due to changes in pressure). When an air parcel cools as it is lifted, its temperature approaches its dew point temperature, the temperature at which condensation occurs. As the relative humidity approaches about 80%, water vapor begins to condense onto hygroscopic cloud nuclei. As the body of air is lifted further, and the relative humidity approaches 100%, and water vapor begins to condense onto even non-hygroscopic particles (for later reference, hygroscopic literally means "water attracting".) As the air is lifted further, the cloud builds upward, towards cooler and cooler air temperatures. Even though water freezes at 0 degrees Celsius, cloud droplets do not because there is no flat surface for to freeze to, therefore there are relatively little amounts of ice crystals around and just above the freezing level. As it progressively gets colder with height, more and more ice crystals are found. This can only be explained by the fact that not only do ice nuclei exist at these levels, but it is cold enough for some of the large droplets to attach to them. At this point, there is still an abundance of cloud droplets. At the -40 degrees Celsius level, that is the point at which water can directly freeze, in a process called deposition. No ice nuclei is needed, which allows water vapor to freeze directly with each other into crystalline shapes. Since this article deals directly with snow crystal formation, I will not talk about this much. This is because most winter storms do not have cloud temperatures below -40 degrees. So then, how do snow crystals form? Exactly as I stated in the first process; This is the one I will elaborate on.
   Ice nuclei are quite rare in our atmosphere compared with condensation nuclei. This can be explained by the fact that ice crystals need an exact crystalline structure to cause snowfall formation. There are very few particles that cause the freezing of water droplets in a crystal shape. Therefore, ice crystals have very little competition for available water. Once water begins to attach itself and freeze to the ice nuclei, vapor pressure around the ice nuclei decreases. Once the crystal forms a flattened, ice crystal structure, the differences in vapor pressure between the ice nuclei and cloud droplets (this means that if the air is saturated with respect to water, it is supersaturated with respect to ice) cause water vapor to "gather" near the ice nuclei (due to the freezing cold temperatures, water tends to congregate in certain areas), and attach themselves to it, also known as the process of deposition. Once several ice crystals have formed on ice nuclei, this sets up the conditions for the formation of new ice crystals. Ice crystals are quite a bit heavier than cloud droplets, and so they fall. Different fall speeds between ice crystals and cloud droplets (and other ice crystals) cause collisions, which shatter the original ice crystal. This sets up an opportunity for new ice crystals to grow, because water droplets will now attach themselves to the shattered fragments. These shattered fragments begin to grow at the expense of the water around them. This process describes how precipitation forms in cold core clouds (temperatures below freezing in the cloud), not just snow. Snowfall requires very precise conditions for formation. At this.. I will leave snowfall formation for the next article. One thing I can tell you though, is that there is a persistent myth about snow in society today. This myth is that snow can only fall when it is below freezing outside.. That is NOT true. And I will explain this in the next article. The next article will focus on winter storm precipitation processes, and how precise conditions have to be for snowfall.