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snowflake

snowfall temp

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Hi, I've just read on BBC that snow falls when it's between 0 - 2 degrees.

Why does rain fall between those temperatures then? I live on the coast, so that is probably something to do with it, but it rained yesterday and Tuesday and the temperature hovered between one and three degrees.

Thanks.

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It will also depend on the temperature of layers higher up.
In winter a lot of precipitation will start as snow high in the clouds.
It's not unusual for surface temperatures to be lower than higher in the atmosphere, in extreme cases this can lead to freezing rain which can be very serious if it accumulates for long.

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Had rain sleet here the other day at 1.5c to 2c.

As for april or may snow can fall up to 9c or higher in may.

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As 4wd suggested it depends significantly on the temperature of the higher layers of the atmosphere: if the precipitation has to fall through a large layer with temperatures >0C then it is more likely to turn to sleet or rain than if there is only a shallow layer of >0C temperatures near the surface, as it takes time for snowflakes to turn to rain.

Another factor is the relative humidity - the lower the relative humidity, the greater the tendency for snow at above freezing temperatures to evaporate rather than turning to rain, and the process of evaporation cools the air around the snowflakes cold.  A general rule of thumb is that if the average of the dry bulb temperature and the dew point, or alternatively the wet bulb temperature, is around or below zero then it will probably snow, but it doesn't always work as a lot also depends on how shallow the >0C layer is.  Being near the coast with an onshore wind often means greater relative humidity than further inland, and also the temperature tends to be raised due to the warming effects of the sea.

I've seen snow showers in the spring months with a temperature as high as 8C, and occasionally even in February.  This is typically due to a combination of low relative humidity and a shallow layer of solar-heated >0C air near the surface, typically if we get a sunshine-and-showers setup from a northerly, or (more rarely) cold zonality as happened repeatedly in March 1995.  In heavier showers the colder air further up tends to be dragged down to the surface through the aforementioned evaporative cooling process, which can lead to some pretty sharp temperature drops.  On Christmas Day 1999 I saw wet snow fall with a temperature of 5C in a chilly westerly regime, but that seems to be the upper limit for December.

As 4wd pointed out if you get a temperature inversion you can get freezing rain, with rain falling at temperatures of around or below 0C, which freezes on impact with the ground.  More rarely you can get ice pellets, where snow turns to rain and then starts to refreeze again as it approaches the surface, and these tend to broadly resemble hailstones.

Edited by Thundery wintry showers

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