During the winter months, there can be a lot more than just rain or snow falling from the sky. WAVE 3 meteorologist Tawana Andrew takes us through the different types.
Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning. Tawana.
Tawana Andrew: Good morning. So in honor of Thursdays' snow, we're talking about, of course, wintry weather for today.
BB: Yeah, we have had a little precipitation over the last 24 hours. So that is our topic. Precipitation types. Enlighten us, please.
TA: So we have to focus, as meteorologists, on not just the temperature when it comes to precipitation, but the amount of moisture, especially in the winter months. So everything from rain to graupel can fall from the sky at this time of the year. But for us to even get an ice crystal in the atmosphere, we need relative humidity of at least 70% in what's called the snow growth, or the dendritic zone. So it's it's in this part of the atmosphere that you have temperatures in between 10.4 and 0.4 degrees Fahrenheit. You need a very specific temperature range and without substantial moisture in this area, most wintry weather. So we're talking snow, sleet. It just won't happen. Now, we all learned back in elementary school that you need atmospheric temperatures at or below 32 degrees for snow to fall from the cloud all the way to the ground, right? But there are situations where snow can fall when temperatures are above freezing. So the first one is that if there's a shallow layer of the atmosphere just above the ground where the temperature remains below 33.8 degrees Fahrenheit, yes, I know, very specific again. So if you have that 33.8 degree temperature or below, then snow can still fall. Now, snow can also fall when you have a wet bulb height below 1500 feet. And basically the wet bulb height is where that evaporative, that word is a little hard for me today, evaporatively cooled temperatures drop below 32 degrees. And in both of these situations, you'll end up with that wet, fluffy snow that kind of sticks to everything a little bit more. Switching gears to sleet. Sleet happens when snow melts and refreezes. But that melting layer has to be thin, has to be less than 2000 feet thick. If it's a little bit thicker than that, then you're going to end up with more freezing rain than sleet, and the temperature within that layer has to be between 33.8 that's that number again, and 37.4 degrees Fahrenheit. Once again, the temperature is getting very specific. This is why the meteorologists get very stressed out this time of the year. Of course, for freezing rain, that occurs when the snowflake will melt completely, but the ground temperature is below freezing. So once that temperature and the melting layer is above that 37.4 degrees Fahrenheit level, then the snowflake will melt. It will become a raindrop. But if there's a layer of below freezing temperatures just near the ground, and that layer is very shallow, then the raindrop does not have enough time to refreeze into sleet, so it just kind of sticks to everything, and then everybody's just slipping and sliding everywhere. So we do not like that freezing rain. You can also end up with freezing rain if that snow growth zone that I mentioned earlier doesn't have enough moisture for the ice crystals to fall. So you just end up with the cold raindrops falling all the way through the atmosphere.
This transcript was edited for clarity
