Im asking because where I’m from ( Baghdad) it snowed for the first time since 1914! Why was this year different? Why hasn’t it snowed before?
In: Physics
In reality, it is always snowing, everywhere except right on the equator.
People think that clouds in the sky form rain. In reality, those clouds are so high up that it is always below freezing, so every single rain, except right on the equator, is actually snow that melts as it is falling.
Therefore only one thing is required for it to snow–that the snow doesn’t melt on the way down (or melt and re-freeze, which makes it sleet instead) Basically as long as the air is cold enough it will always snow instead of rain. So all that is needed is for it to be cold outside.
Checking the average temperatures in Bagdad, it simply rarely gets cold enough. It has to get pretty close to 32F or 0C to have any chance of snowing. In addition, it looks like Bagdad doesn’t get a lot of rain. So in order for it to snow it both has to be one of the few days where it rains AND at the same time it has to be one of the even rarer days where it gets close to freezing in temperature.
The chances of both of these things happening at once as just very, very small. Possible, but small.
The answer is more complicated than it sounds; all kinds of [precipitation types](https://en.wikipedia.org/wiki/Precipitation_types#/media/File:Precipitation_by_type.png) can occur even when the air is below freezing..
Snow specifically usually forms in sub-freezing air when a ice develops on a [nucleus](https://en.wikipedia.org/wiki/Snowflake#Nucleus), making one of several typical snowflake types depending on temperature, humidity, and other things. For it to remain snow there can’t be any melting along the layer unlike some other frozen precipitation types.
I did a quick check of models for the area and didn’t see any major snow producing large-scale events..do you remember what day/time you saw this as this could be useful for understanding why it happened this time? It could also have been [graupel](https://en.wikipedia.org/wiki/Graupel) which many confuse for snow but has rather different physics behind it.
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