Snow Melt

[Stuart]

Melting the snow in the rainguage is an issue we all have here in the rockies. Here's what I've found out. The following information is taken from "Practical Snow Melt Design", copyrite Tesmar Application Technology 1995.

The Davis Rain Guage Heater is a 25-ohm, 24-vac heater generating 75-Btu/Hour.

 Eight inches of snow at 13% water = 5 pound (lb) of ice. The specific heat of ice is about .51 BTU/Lb (One pound of snow will require .51 Btu to raise 1 degree F). 5 lbs of snow at 22F will take about 26 BTU to raise its temperature to just below freezing. To phase change (latent heat of fusion) ice to water is 144 BTU per pound. So to convert 5 lbs of snow to meltwater is: 26 BTU/Sq Ft + 750 BTU/Sq Ft = 776 BTU/Sq Ft to actually melt the snow.

The Davis heater will melt 8" of snow @ 22F in 10.5 hours (776/75). Now the question is how fast and at what temperature is the snow falling, is the wind blowing? A second question is how does the meltwater get out of the guage?  At -20F and with 20mph wind the heater might not be able keep the gauge from freezing up.

[ThorntonWeather]

Interesting question, Stuart.  I don’t really know however, I will say that my Davis heater (two years running) has kept up with everything thrown at it in the Denver area.  I actually suspect it is gets too warm, at least when it goes to precipitation that is falling slowly. 

A case in point was yesterday’s storms where it was slow rain / light snow all day and temps just above freezing.  My Davis recorded 0.26” of precip but folks on CoCoRaHs around me recorded double that.  A co-worker who has the Davis + heater and has a CoCoRaHs manual gauge says he sees the same thing. 

I honestly think it is getting warm enough to evaporate a lot of what falls if it isn’t coming at a fast enough rate. 

   T

[Stuart]

 My Davis rain gauge heater came with a snap action (open-on-rise) thermostat mounted on the heater board inside the rain guage that opens at 110F with a 25deg F differential. This should maintain the internal temp of the rain guage at a high of 110F and a low of 85F. This will melt snow , but seems to be a bit high and I'm sure it is evaporating some water. I'm using an external thermostat to control the internal temperature of the rain guage. It's set to maintain the inside rain guage temperature at 40F with a 20F Diff. (a low of 40F and a high of 60F). I'm using the original snap-stat as a high temp cutout. This is the second winter I've had this controller running and it seem to be keeping up with the snow. The only other rain guage near me is at the airport some 15 or 18 miles to my east. So I have little to compair it with. Here it can rain on one side of the house and be sunny bright on the other.