Snowflakes take an amazing journey
I noticed snow on some of the area hills this past week, and it’s finally sinking in that wintry weather could be upon us any day now. As folks tend to look at the weather forecast and zero in on those subfreezing temperatures, I’d like to remind you all that snowy weather can occur even when temperatures are forecast to be well above freezing.
Recently, one of my children (I should cut her some slack, she’s only 6 years old) mentioned something about snow being frozen rain. As a good meteorologist mom, I corrected her by saying that snow is not frozen rain, but rain is merely melted snow. With the exception of the tropics, all precipitation begins as snow high up in the clouds. When a meteorologist is trying to determine what type of precipitation will fall, the key question is how far down in elevation will the snow make it before it melts. It is just as important to look at how temperatures are expected to evolve in the vertical as it is to see the changes in the horizontal.
Consider an ice cube thrown out on the driveway on a hot summer day. Though temperatures may be 100 degrees or more, the ice will not melt instantaneously. So it is with snowflakes as well. While temperatures may be as warm as 40 degrees at the surface, cooler temperatures aloft may allow the snowflake to survive the entire journey down from the cloud to the ground. The amount of melting that occurs will depend on the thickness of the layer of above freezing air. The process of melting a snowflake takes heat energy – heat which is removed from the surrounding air.
As this happens, the initial melting snow can actually pave the way for later snowflakes to survive longer, assuming the winds are not bringing in a steady stream of warmer air. While surface temperatures below freezing will definitely make a difference in whether the snow accumulates or “sticks,” some of the most damaging snowstorms can occur when temperatures are a couple of degrees above freezing. These heavy, wet snows – in addition to being harder to shovel – can down trees and power lines as well as collapse roofs. This tends to occur more often in the spring, however.
For the upcoming week, it does look like we will have plenty of opportunities to play catch up on our rainfall, which came up way short of average for October. Rain over the last couple of days has given a needed boost to area totals for the start of November. The computer models are keeping temperatures out of the deep freeze for the next 7 to 10 days, so though area ski resorts may start building their snow bases, valley locations will be dealing with more wet and not much white.