Fun Weather Facts: When it Rains it Snows
All of us are familiar with the famous commercial line “When it Rains it Pours.” But, when it comes to weather in the pacific NW we could say “When it Rains it Snows.” Again, from your everyday experience and from what I’ve already blogged about, you are ready for this next “Fun Weather Fact.”
You need to remember driving over Snoqualmie Pass in the winter when it is snowing at the pass, but raining in where you came from, and think about what was hitting your windshield. First, of course, the windshield wipers were swiping rain off of the windshield. As you continued to climb towards the pass the raindrops all of a sudden became much larger and started to hit the window in big patches. Next, you began to see small pieces of ice in the larger drops, then more ice in the drops until large-wet snowflakes appeared.
As you kept climbing, the wet snowflakes turned to all snow. So---what is happening?
What you experienced is the same as if I caught a hook under the back of your pants on a rainy day and pulled you off of the ground and straight up into the atmosphere. In my last few blogs you learned why the air can get colder with height and not overturn. As I pull you upwards, at some point in your upward journey the air temperature will fall below freezing.
This is called the freezing level.
In summer the freezing level is very often higher than 10,000 ft, but in winter it is normally around the height of the mountain passes. Eventually, in summer or winter you will pass through the freezing level and find it is snowing all around you.
As you rise toward the freezing level you will first go through the layer where the snow is melting and turning into rain. That explains the big raindrops just below the freezing level (melting snowflakes first turn into giant raindrops, then break up into smaller drops as they continue falling). Higher up, but still below the freezing level, large raindrops mixed with ice pieces are snowflakes that haven’t completely melted yet.
So---now you know. Since precipitation develops high up in the atmosphere and mostly above the freezing level, even in summer when it is raining on us somewhere (in an atmosphere far, far above) over our heads it is snowing.
In the tropics rain can fall and never have once been a snowflake, but that is a tale for another time and place.