COOP reports

[snowfan470]

Hi John,

Knowing that you worked at the national weather service for a time, is there a certain guideline/methods that the COOP observers have to follow for measuring snow? Correct me if I'm wrong, but I believe your supposed to measure at multiple spots within an area and then average the amounts for snowfall reports. I was looking at the COOP reports for bergland dam and twin lakes for the last month (Jan 12 - Feb 12), and something has to be wrong with one set of the data. Bergland in this time frame received only 51 inches of snow, with a water equivalent of 6.14". Twin lakes on the other hand is reporting 102.9" with nearly an identical water equivalent of 6.10". If you calculate the average ratios for that entire time period, bergland has an 8.30:1 ratio, which completely doesn't make sense for lake effect snow. Twin lakes has a ratio of 16.86:1, which is more on the order of lake effect. Have any idea of what might be going on here? How do they measure the water equivalent of the daily snowfall anyways? I know that snow totals can vary significantly from one location to the next, but a 50" difference seems quite drastic, and the ratio doesn't make sense for bergland. The snow depths however, do make sense.

Bergland - http://mesonet.agron.iastate.edu/COOP/cat.phtml?station=BERM4&year=2013&network=MI_COOP
Twin Lakes - http://mesonet.agron.iastate.edu/COOP/cat.phtml?station=TLKM4&year=2013&network=MI_COOP

-Dave

 

[jd]

That's a nice observation and a good question. First, there are guidelines that a COOP Observer has to follow when making observations for the NWS. I actually am not part of the COOP program and never dealt with it when I worked for the NWS, so I do not know the exact details of the training they use, but yes, an observer is suppose to take several measurements for snow depth/fall and compute an average.

I really do not know the answer as to why there are the differences in SWE (snow water equivalent) though. It would stand to reason that the Twin Lakes SWE would be closer to what is should be, but then again, they do get more LES than the Bergland Dam area, so I suppose it's possible that both measurements are right on.

I actually just took a core sample of my snowpack this afternoon and it is in the process of melting. I will be taking a SWE measurement from that core for a different NWS program once it all melts and can report back what my SWE is tomorrow.

-John

 

[Skylar]

Thanks for the link!

 

[snowfan470]

Thanks for the reply john! I'd love to hear what your SWE value is. What NWS program do you measure SWE for? I actually like to view SWE data as the better indicator of snow pack "quality" for snowmobiling, b/c more SWE = more dense snowpack = better snow base for backcountry riding (excluding a snow pack that just had an inch of rain fall on it)! A lot of the complaining that goes on (early in the season) is because most people judge snow on snow depth rather than SWE, and then people complain b/c the backcountry riding is no good even though 3 ft of snow just fell. Getting back to the topic, just based on the data from Twin Lakes and the average snow ratio from that site, I think I'll trust that data more. I know twin lakes does get more snow than bergland; however considering Bergland's snow total and SWE total from the last month, an average snow ratio of 8:1 from that data seems way to low for the dendritic type snow that typically falls during lake effect snow events. But as always, I trust your data the most, and look at it on a daily basis!

Skylar, incase you didn't know, this site http://www.nohrsc.noaa.gov/interactive/html/map.html is also excellent for snow data. In the drop down menu called Select Physical Element, you can choose to view raw snow observations too from the last 24 hrs (most are COOP reports). I usually like looking at the raw snow obs because the shaded data you see when you first open that site is actually modeled data from NOHRSC's SNODAS system, so in many cases, it does contains error! However, the Iowa mesonet site is a good site for archived data in case you want to view past data from previous lake effect storms in locations other than John's residence of course!

 

[mezz]

How do they measure the water equivalent of the daily snowfall anyways? -Dave

Dave, as a coop observer for the NWS, the daily SWE (snow water equivalent) is measured by collecting the amount of snowfall measured & placing it in our rain gauge overflow collection tube & allowing it to melt & measure the water in the rain gauge itself. The process can be sped up if you take a measured amount of warm/hot water & add it to the snow collected, then remove the same amount of warm/hot water added by measuring it out in the rain gauge, the remaining water is the SWE for that period of snowfall. As you may already know, LES & system snows are two entirely different animals when it comes to the SWE, the LES is generally the drier variety.-Mezz

 

[jd]

Well Dave, here is some more uncertainty for you.

Out of the 33" of snow on the ground, I melted down to 4.0" liquid.

Keep in mind that rather than melt down daily totals and add them to compile a SWE, I take a core sample of the entire snowpack and melt that down. So there is going to be a loss due to sublimation (snow evaporating) and even melting over the course of the season to date.

-John