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Snow melt today

Posted Sun 18th March 14:06

Despite temperature being well below 0C (32F) snow is melting today. That shouldn't be happening, should it?

Snow melting below freezing point

Dry and powdery snow fell in much of the UK last night. On the hills surrounding Berkhamsted accumulations totaled close to 3 inches and temperatures have stayed well below 0C (32F) today. Despite that pools of water have formed on some concrete, tarmac and stone surfaces. The picture below shows dry snow on my lawn but a damp footpath bordering it. The snow is melting and not evaporating due to sublimation, so what is the cause?

Storage heater effect?

Before the cold air arrived it yesterday it felt pleasantly warm for several days and I suspected ground temperatures could lead to snow melt. We're now almost as close to the summer solstice as the winter solstice and solar input is increasingly powerful. Therefore I used a thermal imaging camera to take some pictures.

The one below was taking on Thursday 15th March and shows part of my vegetable patch! The temperature reading is +9.9C, although some surrounding areas are about 2C lower.   

The picture below was taken at the same time and shows patio stones. In this instance the temperature reading is +13.2C with surrounding areas several Celsius higher. 

Therefore the stone surfaces are warm and I suspect that heat has been slowly released during the last 24 hours and is one of the causes of the melting snow.

There has also been some snow melt on the lawn (since I started writing this piece actually) despite the air temperature being -1.9C and the dew point -5C.  So it looks like stored warmth is proving to be a big factor.

Another couple of possibilities I can think of are:

1) The overcast skies are leading to heat being radiated back down to the surface.

2) Despite the overcast skies there is still sufficient solar input to lead to snow melt.

I saw similar conditions during the first couple of days of the late February "Beast from the East" cold spell. By days 3 and 4 the melt had completely stopped. To me that suggests ground temperatures had fallen with much of the stored warmth released.   

TL;DR

Despite sub-zero temperatures snow has been melting on some surfaces today. The most likely explanation is a "storage heater effect" with retained warmth being released by tarmac, concrete and stone surfaces.

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geordiesrgr8 7 years ago Show replies(0)

Just seen the first paper reporting the hottest summer for 100 years,

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