SNOWFALL
Throughout the years of weather data collection. Several primary parameters are recorded. Temperature, Precipitation, Snowfall.
While all data is subject to human error, device error, poor site location. In general temperature and rainfall are recorded with a higher degree of accuracy vs snowfall. Snowfall is more labor intensive and demanding and subject to multiple observer methods of recording. Subject also to site impacts, such as open and windy location or even one with too many trees.
Labor intensive? If one wants to have good snowfall recordings you MUST be aware of what’s going on at your recording site at all times when snowfall is occuring. Be aware of:
▪︎Temperature
▪︎Wind
▪︎When the snow stops
▪︎Boardsweeps on your snowboard(not the kind you slide down a slope on)
▪︎Most importantly you need to be present or have a backup observer with knowledge. It’s not always possible to be at your location when needed.
The NWS guidelines for snowfall measurements are in the link attached below:
https://www.weather.gov/gsp/snow
Some snowfall data is official and goes in to the record books. That comes from local NWS coops, cocorahs observers. Some is non official by highway departments, resorts, hobbyist, etc. Just because it’s official, does not mean it’s accurate or methods haven’t changed. Just because it’s non official, does not make inaccurate. Note your methods of snowfall observations are important.
What can make snowfall measurements vary so much? I mean go out and stick a ruler in the ground, right?
▪︎ A non official measurer may simply measure in the grass. Report here’s my tally. Grass will inflate numbers 100% of the time.
▪︎ Location may impact. Ridge tops, open exposed land can create a much more difficult recording location due to wind impacts. Even when winds are light, and if the snow type is light. The ridgetop, even when blowing and drifting isn’t a major impact, will almost always have a more settled snow than a slightly more protected spot where it doesnt settle as fast. One way to eliminate that impact some is 6 hour boardsweeps. Guidelines allow for up to 4 boardsweeps per day. If you do more than 4, you will have inflated numbers. The reason for this is to have everyone on a general guideline for comparison.
Non official is different. The MD highway department, not an official snowfall data site. Does boardsweeps every 2 hours to document for material usage on roadways. Sometimes this leads to numbers that are a bit inflated to what you think you have. Doing a boardsweep every 2 hours and tallying those totals over a day, 2 days, will create a tally at times a fair amount higher than what you record recording once or 4 times over 24 hours. Also, I do believe the SH marks sleet in the ice category vs snowfall. Sleet is officially recorded as snowfall. Freezing rain that is liquid freezing on contact is the only thing that’s actually ice.
One area that is sometimes difficult in recording snowfall is being present for the max snowfall. Going by official guidelines, you want to capture the instantaneous max within your boardsweep period. In personal preference, I do 2 boardsweeps per day. In a valley with light wind impacts, open and fairly protected it works well with the day schedule.
Capturing that instantaneous max is sometimes tough. Maybe it happens while you’re at work, or asleep. Back in late November we had a snow event that really hammered it down from evening through midnight. Temps then went to and above 32° and the snow started to compact. My measurement for my max snowfall was reached at 2:30am. Head outside when you need to, to capture that. By 7am, that snowfall had compacted on average 1-2″ over the 4.5 hour period. A 7am obs would have led to a lower report.
Snowfall is measured off a snowboard. (Snow depth is not) This is a basic guideline again in attempt to get everyone using the same method for comparison. The snow board should be in a site of least wind impact. Also not impacted by an obstruction above such as a tree or house. That will lead to a unreliable measurement. If possible avoid decks. Any wind often blows snow off your roof on to the deck. A sleet event with a steep roof can really cause a pile on your deck. There are occasions that’s a fine spot to measure. Such as a calm wet accumulation, but it’s often a uneven playing field measuring around a building.
Collecting the SWE(SNOW WATER EQUIVALENT). That’s done with either a 4″ style cocorahs gauge or even more accurately a 8″SRG(Standard rain gauge) used by coops. 8″ is preferable, but 4″ is reliable and needs to be watched for overflow with a big snow and the building up of snow on the rim. Then you do your best to divide that up in to the can to melt or weigh for your water equivalent. You can measure snow without worrying about the water equivalent. One method that does not work and I see people do this. They have tipping bucket gauges that become inoperable in cold weather, and only a portion of the fallen snow gets in them. Most blows around or out. They aren’t designed to catch snow. A higher mounted one is even worse yet. Then on warm days, the snow that remained on it, is marked down as the melt/water equivalent of the snow. Official locations will not do this, but some hobbyist that are unaware do.
When looking at snowfall data. Do you find a graph or chart online and take it for what it shows. In general, most do. Most do not question data. Its almost as important knowing the meta data(data about data) as it is knowing the data you are viewing. There have been snowfall graphs circulating recently and they have “no source”.
The first thing when looking at past snowfall data is:
▪︎ know the source.
Anyone can jump online and view data through the great work of all the coop observers, and cocorahs observers. Some stations go back 100+ years.
Great sites are:
https://www.weather.gov/wrh/climate?wfo=lwx
https://www.weather.gov/wrh/climate?wfo=rlx
https://www.weather.gov/wrh/climate?wfo=pbz
https://www.weather.gov/wrh/climate?wfo=ctp
and if you want the original forms by observer. I like it for the nostalgic purpose
https://www.ncdc.noaa.gov/IPS/coop/coop.html
That said , just because you can whip out a snowfall graph or chart off a particar station and think, I got a apples to apples comparison from 1898 to 2024. The reality is, you likely do not.
Observer methods vary!
There were observers who used a straight 10 to 1 SWE for snowfall. If they had .4 melt. They marked down 4.0″, .2 melt they marked down 2.0, 1.1 melt they marked down 11.0″.
This was fairly common in some older data. We know snowfall of 10 to 1 actually isn’t all that routine. Many times we see 12 to 15, 15 to 20 to 1, even 25 to 30 to 1. In simply using a straight 10 to 1, your snowfall tallies will be low. Over a season, very low vs reality. When you look at historical graphs, you may say ” oh wow”, it didn’t snow much back in this year or that year. 1 reason tallies may be as low as you see might be the observer method.
View example below :
▪︎Another reason is simply in plenty of instances, a station will see dates marked by the letter M. Which stands for missing. Meaning maybe it snowed or maybe it didn’t snow, you just do not know. The observer did not have a obs for that day or sometimes left it blank if nothing occured. A 0 vs M should always be used in that case. If you see a “M” you can hop to a nearby station and if you see an accumulation there and the other site had a M, you can assume those tallies are low at that site.
▪︎ Even within the same station name. Stations are often took over by other observers. There is a distance and elevation criteria that needs to be met for that station to retain its name.
https://www.ncei.noaa.gov/access/homr/
Let’s look at Oakland site moves, all considered the same station:
Even when that’s met, while temperature and precip shouldn’t vary significantly.(THERE ARE EXCEPTIONS- Oakland is 1. You can’t compare the current Oakland data vs old Oakland data) Exposure of the site and method of the new vs old observer can impact reported snowfall. In many cases we do not know the method of data long ago. Some can be seen within its own data. Not all.
You can nearly say that 100% of the time, when an observer and site change occurs. Those numbers wouldn’t match the old observer and site. That’s the variability with snowfall you don’t have with other parameters. Thats why snowfall data is simply the least valuable data set. It has value and in most instances very snowy years vs non snowy years are easy to see.
More obs variability. Let’s hop to our current Snowshoe coop. Back in October, we had the mid month high elevation snow event. Snowshoe marked 0 depth that entire week and only .1 accumulation. Odd. Then I noticed the mins were much lower than what was occuring across the high ground. Something was amiss. I contacted Charleston. They were going to look in to it. My suspicion was the site moved to a valley. The response later that day or the next day was. The site was moved to the base of Silver Creek from the summit of Snowshoe. It exceeds elevation and distance criteria but retained the same name. The response stated precipitation was still being recorded at the top of Snowshoe. That’s a unknown as it appears snowfall is not. Hence the lack of October accumulation. For recent years Snowshoe only reported to the nearest half inch or inch. Recently there was a 3.8. Another reason snowfall data appears to be at the Silver Creek base. Over the season that will alter comparison to the old site. Temps will be a big impact as well. This eliminates accurate comparison over the years.
Now the Snowshoe coop season to date has reported (today is December 13, 2024)
Get ready 28.4″
The resort also keeps track of snow and in my eyes, appears to be a bit more in line. Granted it’s non detailed. All to the inch. But the resort has reported
drum roll…………..
48″. A 20″ spread season to date from the resort and the coop.
Yes. Snowfall is the least valuable data set because of the variability it contains, observer method and at times it’s pretty extreme.
Allegheny Mountains Weather 