WTF?! Edmonton currently has a freezing rain warning! :eek: Excuse me?
It is December 8, currently minus 10 degrees Celsius (14 F for you folk south of the border), and raining (according to Environment Canada - I haven’t actually looked or ventured outside)!
How can it possibly be raining??
Yes, it’s a serious question (although I guess it could qualify as a Pit-able complaint too :D). In case it helps you to answer, the dewpoint is -16 C (3.4F), humidity is 61%. If something wants to fall out of the sky, why isn’t it snowing instead of raining?
Yeah, I saw that: “Cloudy with sunny periods and 60 percent chance of snow or freezing rain. High minus 8.” I think they’re pretty much guaranteed to be correct somehow
Need a meteorologist here. But freezing rain occurs when precip falls out of warm layers into sub-zero layers near the ground. It is cooled below freezing, but still liquid. When it hits the surface it instantly freezes.
On the way down, it doesn’t cool enough to be frozen precipitation. It starts warm and cools on the way down and hits surfaces that are sufficiently cold to eventually (rather quickly) freeze it.
It probably does not freeze instantly.
E.G., Warm water in a Zamboni is surrounded by freezing temps and comes out into a cold environment, lands on a frozen surface and freezes later. It takes a couple of minutes (at least), but it freezes. Freezing rain is similar. Starts out warm, in a warm environment surrounded (or bound for) a cold environment.
Temps are temps in the air, near the ground, as published by weather people.
We had a similar thing in the UK a few days ago, but the surface temperatures were not so low. The temperature on the ground really just reflects the temperature of what can be a very thin layer of air. As a warm front moves overhead, the warm air often rides over the denser, colder air at ground level. A mile or so up in the air, where the rain clouds are, the air can be significantly warmer than the air at the surface. This is the opposite of the usual scenario, where the “mile-high” temperature is about 8-10C colder than the surface air, generally speaking.
If precipitation starts as rain (i.e. if the upper air is above freezing, as a rule of thumb), it might turn to soft hail (graupel) or ice pellets, but you won’t get fluffy snowflakes forming unless the upper air also cools. If it doesn’t have time to solidify before it reaches the ground, but the ground is still cold enough, chances are you will get freezing rain.
Conversely, when the upper air is much colder than the ground, as is more usual, it can be raining at ground level even though the temperature where the clouds are is several degrees below freezing. So when it rains in winter, that rain often started out as snow.
Just to round out the answers. Freezing rain consists of supercooled rain drops which are drops of water that are literally below the freezing point but remain liquid because they lack a speck of dust or something around which ice can form.
Wikipedia references:
Edit: Some of the previous answers imply that the rain isn’t actually below 0C but is landing on freezing surfaces which causes it to freeze. This is not the case, in freezing rain the rain itself is below 0C.
In order for it to snow, ice pellets must form in the clouds. Snow is not just frozen rain. If the temps in the clouds are sufficiently below freezing, ice crystals will form. When an ice crystal becomes heavy enough, it will fall as a snow flake. (Look at a snow flake and you will see it is in a crystal form, unless it has merged with other flakes falling due to partial melting. If the precip starts as rain, it will never turn into snow, but it can become various forms of frozen precip: sleet, graupel, or freezing rain (if it freezes upon landing). It cannot form into hail, although graupel may be called “soft hail.” Hail is formed when raindrops in the lower part of a cloud is uplifted by convection into a higher part of the cloud where it freezes. The drop then begins to fall, but is caught by another updraft. And so on, until it is too heavy to be lifted up again. Then it falls as a hailstone.
