Weather and snowfall measurements
Waterbury,
VT
Elevation: 495 feet
Geography: I make weather observations and measure snowfall from storms in my back yard in the town of Waterbury in the state of Vermont. The map above on the left gives the approximate location of our house. Quebec, and some of the surrounding states in the Northeastern United States are labeled for reference, with the thicker green border lines indicating the state and international boundaries. Also shown on the map are counties, indicated by the thinner green lines. Our house is located very close to the border between Vermont’s Chittenden and Washington counties, and as with many other borders in the state, there is at least a partially geographical basis for the county line. The division between the counties of Chittenden and Washington is very much in line with the spine of Vermont’s Green Mountains, which run generally through the center of the state from north to south. We are located at an elevation of 495 feet along and a bit up from the Winooski River, which runs through the area at an elevation of roughly 380 feet, and eventually flows down to an elevation of 95 feet where it dumps into Lake Champlain in the Burlington area about 20 miles to our west. The Winooski Valley is a major route of east-west travel through the area, as the river has cut a deep swath through the Green Mountains. Our location is sandwiched between some of the highest peaks in the range, with Mount Mansfield, the highest in the Green Mountains at 4,395 feet about 10 miles to our north, and Camel’s Hump, the third highest peak at 4,083 feet about 4 miles to our south. Another important local peak is Bolton Mountain, which is about 6 miles to the north of us and 20th in height among the Green Mountains, rising to 3,680 feet. Bolton Mountain sits at the head of a long box-canyon type valley (Bolton Valley) that also contains the local ski area of the same name. The Green Mountains form an impressive wall with roughly 4,000 feet of vertical relief above the lower valleys in the area, a setup that is well known throughout the region for producing notable orographic enhancement of snowfall. Indeed, the Green Mountains, especially those north of the Winooski Valley, are famous for having some of the highest annual snowfall totals in eastern North America and average more than 300 inches of snowfall each year. Our location, although relatively low in elevation, is in line with the Green Mountain spine and appears to get in on some of the orographic precipitation enhancement caused by the mountains as storms are squeezed through the Winooski Valley. The image below is taken above the dam on the Winooski down below our house, and gives an idea of some of the local topography as you look up from the bottom of the valley. Since there are no major mountains directly to our west, we also appear to avoid most precipitation shadowing. Although at our elevation we do not get as much snow as is seen higher in the mountains, we generally get much more snow than locations to our west in the Champlain Valley that are at similar elevations. For example, the National Weather Service office in Burlington is located at the Burlington International Airport at an elevation of roughly 330 feet, and the annual snowfall average is 81.0 inches. In contrast, the average annual snowfall at our location on the Waterbury-Bolton line is over 170 inches, with our highest season total since 2006 being 203.2 inches recorded during the winter of 2007-2008. I discussed various aspects of our location's snowfall in a post on the Liftlines Skiing & Snowboarding forum. Scott Braaten, one of our local forecasters, observed that our house seems to be located in a part of the Winooski Valley that receives some of the most intense snowfall due to upslope enhancement, and that prompted an easternuswx.com post about our local geography and what might be enhancing our snowfall. Scott also provided some nice insight in a follow up post, and included a map showing some of the snowfall trends he'd observed in his daily trips through our area to Stowe.
A view from the floor of the Winooski Valley
(elevation ~380 feet) down below our house in Waterbury
Snowfall Collection:
I have an elevated snowboard (pictured below) in the back yard, which is just a
white board made of plastic building material affixed to a pole. The snowboard platform
was initially about 34 inches above ground level, a somewhat arbitrary height
that came about simply because that was the point at which the pole had sunk in
the ground enough to be stable, and it seemed like a convenient level for
reading snowfall measurements with a ruler without having to bend over too far.
Although I didn't know it when I set it up, that board height of approximately
three feet was rather appropriate for our location; it seems that on average,
our snowpack tops out at close to three feet each winter (see the table
containing snowfall and snowpack data below on this page). The deepest snowpack
I've recorded at the house since I started taking measurements in the winter of 2006-2007
is 40.5 inches after the March 5th,
2011 storm, although also of note is the depth of 37 inches that was
reached after the February
2007 St. Valentine's Day Snowstorm and again after the March 2007 St. Patrick's Day
snowstorm. Since the point at which we moved to this location in October of
2006, that Valentine's Day
Storm still stands as our greatest individual snowfall event, delivering
29.2 inches of snow. So, the snowpack in the yard has occasionally reached a
level slightly above the board, but it hasn't been so far above it that the
board has ever been buried. In the summer of 2009 we installed a new deck out
back, and the snowboard is now affixed to the deck as shown in the image below.
With the support of the deck, the pole does not need to be sunk into the ground as deep, so the snowboard stands higher above the ground now. I haven't checked it, but it's probably over 40 inches in height above the ground, which will be useful since the snowpack depth has surpassed 40 inches here. With regard to snowpack depth and board height, there are a couple of things to note about this type of stationary snowboard setup. Throughout a long winter of snowfall, the snow that has been collected on the board and pushed onto the ground will actually create quite a mound, so one may find themselves having to push that pile of snow back or knock it down so that it doesn't impinge on the board. The other thing to be aware of is that constantly walking to and from the board and working around it all winter, will heavily compact the snow on the ground around the board. I have found that even this compacted snow can reach a considerable height, such that one will eventually have to crouch down quite low if they would like to look at their ruler from a height level with the board. I recommend keeping up on the shoveling around the board as much as possible throughout the winter to avoid this buildup, because it doesn't take long for the snow to reach a density akin to glacier ice, and then it can only be removed with the help of something like a pickaxe (which I've actually had to use on occasion). With the updated setup of the snowboard attached to the end of the deck, this is no longer much of a problem as long as I keep the deck clear of snow. Along with my elevated snowboard, I will often use the more traditional method of collecting snowfall on a snowboard that is simply placed on top of the existing snowpack (or the ground if no snowpack has been established). The ground-based snowboard technique is a bit more of a hassle because it can be frustrating to try to get down level with the height of the board and get a nice level look at your ruler, especially if you like to record the snowfall down to the tenths of inches. Also, ground-based snowboards have to be picked up, cleaned off, and then replaced on top of the snowpack in a nice level spot (which can sometimes be hard to find if your snowpack is disturbed by foot traffic etc.). Ground-based snowboards will also become buried after each snowfall, so one may need to flag them to find them. Finally, due to the very dry, fluffy upslope snow that we can sometimes receive, replacing the ground-based snowboard cleanly can be a bit of a challenge because it can be hard to get the snowboard to sit on top of the snowpack without sinking in. If the snowboard sinks into the fluffy snow, the snow often sloughs in from the sides and fills the snowboard, and you don't have a clean snowboard for snow collection. However, a ground-based snowboard does have a couple of advantages over an elevated one. In snowfall events at temperatures above freezing, a snowboard sitting on the snowpack will help to prevent the snow on the board from melting, since the board is cooled by the snow beneath it. The snow on an elevated board is exposed to the warm air on all sides, and will melt and compact more in above freezing temperatures – if you are not able to watch the board at all times, you may not catch the maximum snow accumulation before it melts down. Another advantage of a ground-based snowboard is that it may be more protected from the wind, which is something that can be quite a hassle with regard to snow collection. Fortunately, our location is down in a fairly narrow valley surrounded by lots of trees, so we don't get much wind even in the biggest storms, and that makes monitoring snowfall much easier. If wind is an issue in a location, the more accurate technique for snowfall measurement is to collect snowfall on snowboards at five separate locations and then average the results. In our case with our whole yard being very sheltered from the wind, I haven't found the need to put out a lot of different snowboards because the accumulations of snow are very consistent throughout the property. However, I do have a couple of ground-based snowboards that I put out back and monitor just to confirm what I get on the elevated board, and also to serve as a backup in case the occasional gust of wind affects the stack of snow on the elevated board. So, my accumulations are based mainly on my one snowboard in a fixed location, but they are supplemented with information from a couple of ground-based snowboards as necessary.
Snowfall Measurement:
I determine the depth of the new snowfall on the snowboard using similar
methods to what the National Weather Service
uses. There are official measurement sticks for snowfall measurement, but I
measure snowfall with a navigator's ruler that is incremented in tenths of an
inch (instead of the more typical sixteenths), wipe the board clear, and let
the snowfall accumulate again until the next measurement. There is a picture of
the ruler below for those that want to see what it looks like. Reporting in
tenths of an inch is the "standard" from the guidelines I saw, but
people do report in other increments (nearest inch, nearest quarter inch), and
there are also tables out there on the web that list the conversion of
sixteenths into tenths if you want to measure snowfall with a standard ruler. I
just found it less of a hassle to buy a tenths of an
inch ruler for a few bucks and use that for my measurements. The NWS snow measurement
guidelines I've seen indicate that the minimum interval between
measurements should be six hours, so that is the protocol I have followed. In
many cases, the interval for my readings is in the 12-hour range (such as work
days) or even the 24-hour range or longer (such as being away on trips). So,
the snowfall I've recorded might be a bit low relative to the numbers I might
have obtained if I could be at the board every six hours, but that's life
unless you can always be at the board or have an automated system.
The Snowfall Data:
With regard to snowfall comparisons, there are a couple of different
comparisons to think about: If you want to compare the snowfall from different
years at one location, just being consistent in your measurement approach will
probably suffice. However, if you want to compare data that you obtain at your
location to other locations, you will want to be very careful with the method
you use and match the technique (especially snow measurement interval) used by
the other locations or the comparison may not be very valid. Some places will
take snowfall measurements only twice a day, and some will even take them only
once a day. The longer the time is between measurement intervals, the more
chance there is for the snow to compact or "settle", so depending on
the type of snow that fell, this may make a difference. So, my data might be
useful to compare snowfall in my location to what falls at the National Weather Service Office in
Burlington, where they take six-hour measurements (or places like ski areas
that may do the same), but it could be elevated if compared to places like the Mt. Mansfield Stake or
some of the stations that report the hydrological observations, where they may
measure only 24-hour collections. With that said, I've done comparisons of some
of my six-hour measurements to accumulations in the driveway after 12 or 24
hours, and they have been very close on the occasions I checked. But, there are
probably some storms where settling will be more of an issue than others
because of the snow density. Below I have included a table summarizing various
snowfall and snowpack data collected at the house each season, with maximum
values for each parameter shown in green and
minimum values shown in red. Below the table is
a chart indicating the monthly snowfall means at our location based on my data.
Liquid Equivalent Measurement: At the end of 2009 I started recording rain and snow observations for CoCoRaHS, the Community Collaborative Rain, Hail, and Snow Network. I use a standard CoCoRaHS-style rain gauge (pictured below on the left) to collect rainfall, or any precipitation that is too fluid to collect on the snowboard. While it is possible to collect snow in the gauge and measure its depth, I’ve found that this is generally ineffective and does not catch all the snow for at least two reasons: 1) if there is any wind at all, the snow may be falling at an angle to the opening of the gauge, reducing snow catch, and 2) even though the rim of the gauge is fairly sharp, it’s not sharp enough to prevent all snow from collecting there, and light, fluffy snow will readily accumulated on the rim and eventually even clog the gauge. A picture showing both of these phenomena in play is below on the right. For these reasons, I always measure snow off snowboards, which do not have these problems. The rain gauge is critical to have though if you want to collect all precipitation – it can even be a necessity in mixed storms, where if enough rain falls to melt the snow on your snowboard, you will have lost that liquid.
Since most snowfall is being collected on snowboards, the method for determining the liquid in that snow is to take a core sample of the new snow, melt it down, and determine the volume of liquid. This can actually be done with the CoCoRaHS rain gauge show above, one simply takes the outer cylinder of the gauge, pushes the open end down into the new snow on the board, melts down the core that comes out, and then pours that water into the inner cylinder to determine how many inches of liquid were in the snow. This method works fine, although the cylinder is somewhat large to use on small snowfalls, and I prefer not to have to take my rain gauge down every time I want to get a core of snow off the snowboard. Instead, what I do for getting the cores off the board is to use one of those Adjust-A-Cup-style measuring cups that we had around in the kitchen – a couple of pictures are below:
One just extends the outer sleeve of the cup to provide a tube as shown in the image on the left above, then sticks that down in the snow to get the core. I then press down in the inner tube to compress the snow into a nice disk – similar to what is shown in the image on the right above, of course in the case of snow the disk will be white. I like the Adjust-A-Cup as a tool because it lets me pop out the snow core easily, and it’s relatively easy to analyze small amounts of snow since you can use the inner cylinder to support very thin cores. However, you can essentially use any straight tube/hollow cylinder for snow cores as long as you know the inner diameter – even a toilet paper roll would work for dry snow, it’s just not going to be extremely sturdy or last very long. If the snowfall you are measuring was very minimal and/or the snow was very dry and fluffy, you can stack several cores to ensure that you have enough liquid for measurement - just make sure you know how many cores you stacked for your subsequent calculations. After compressing the core(s) in the Adjust-A-Cup, I pop out the disc of snow into a round-bottom measuring cup – any similarly-sized container will do, but a round bottom vessel is nice for getting out all the liquid. Then, to melt the snow I zap it in the microwave for anywhere from 30 seconds to 2 minutes depending on the volume of snow – you want to heat the snow until it just melts, because you don’t want to lose any of the liquid to evaporation. You can also just let the snow sit in a warm room, or add a known volume of hot water to melt the snow. The resulting liquid is typically anywhere from 0.5 milliliters to as much as 50 milliliters or more, depending on the depth of the snow, density of the snow, and how many cores you stacked. I measure the volume of the liquid with a serological pipette since I have easy access to those, but anything capable of measuring volumes of liquid down to a tenth of a milliliter should work fine. So now that you have measured your liquid, how do you find out how many “inches” of water is in there. To do this, you just need to do a little geometry. Using the diameter of your tube, you can get the radius, and then calculate the area for the cross-section of your tube by using area = pi times radius squared. Multiply this by the height in which you are interested (an inch), and that will tell you the volume of an “inch” of liquid for that size tube. Whatever portion of that volume you found in your core (accounting for multiple cores if necessary) is how much of an “inch” of liquid you collected. I converted everything (area, height, etc.) to metric because I measure in milliliters and that’s what I typically work with, but it could be done with other units. For example, my Adjust-A-Cup has an inner diameter of 6.8 centimeters, which means the radius is 3.4 centimeters and area is 36.3 centimeters squared. An inch is 2.54 centimeters, so that is my “height”, and multiplying the area by the height reveals a volume of 92.2 centimeters cubed. It helps to know that a cubic centimeter is a the same thing as a milliliter, so that means that an inch of liquid in my tube has a volume of 92.2 milliliters. So, if my snow core melted down to produce 92.2 milliliters, that means that there was an “inch” of liquid in that stack of snow. Likewise, if my snow core melted down to produces half that amount (46.1 milliliters), that means that there was a half inch of liquid. Typically, liquid precipitation is reported down to the hundredth of an inch, and in the case of my setup, every 0.922 milliliters measured is a hundredth of an inch. This number will be different for every diameter tube, so you just need to calculate it once for your tube. I set up a Microsoft Excel spreadsheet that takes care of all the calculations for me, including the number of cores I stacked, so all I do is enter the volume I obtained and the number of cores, and it immediately calculates how many inches of liquid were in my snow core. Combining this number with the inches of snow collected on the board can actually get you your snow to liquid ratio, or the “percent water” in your snow, which is really fun to know (especially if you are a skier and like to ski fresh snow). If you picked up 10 inches of snow, and your core melted down to half an inch of liquid, that snow to liquid ratio is 20 to 1, and the snow density is 5% H2O. If doing out all the calculations seems daunting, remember that you can just use a CoCoRaHS rain gauge for cores as I described above, and you don’t have to worry about any calculations because it is all calibrated for you.
Amount of snowfall vs. number of storms: Since in addition to snowfall amounts, I record the number of accumulating snowfall events (weather systems that produce at least a tenth of an inch of snow) each season, I was interested in analyzing the correlation between these numbers. While our area can receive rain and mixed precipitation (rain/sleet/snow/freezing rain) during the winter, systems that produce purely rain are rather infrequent during the heart of winter. In some winter seasons, we may have several events producing some mixed precipitation, while in other seasons, such as 2009-2010, we may be north of the predominant storm track, meaning fewer overall storms, but the precipitation we do receive is mostly snow. Which pattern ultimately delivers more snow? Although the data collected are not perfect for this analysis, since they only include events that have at least a tenth of an inch of snow or sleet, and not events that feature purely liquid precipitation, the results are still informative. As of the 2010-2011 winter season, the five seasons worth of data in the plot below indicate that there is a strong linear correlation (r = 0.9625, r-squared = 0.9265) between the total number of snow or mixed precipitation events and the total amount of snowfall. The linear fit to the data is significant, with a p value of < 0.0001. From the equation for the line fit to the data, one can also get the average amount of snowfall that we receive per storm (the slope of the line indicates that we get approximately 3.9 inches per storm). The bottom line is that regardless of the type of pattern we are in, one that is mostly snow, or one that features some mixed precipitation events, more storms means more snowfall.
Snow Depth: I also record the depth of snow on the ground at our location using a Snow Gauge measurement device (see the first picture below). I've placed this gauge in a representative location that is open to the sky, although partially sheltered on the sides by some trees. The spot seems to be very representative of the snowpack in the yard, and is neither the first place nor the last place to melt out in the spring. This gauge stops at 30 inches, so when our snowpack gets deeper than that, I use a 4-foot metal ruler (pictured in the second image below). I also use this ruler to check the depth of the snow throughout our yard, as it is sharp and stiff enough to cut all the way down to the ground through layers of dense snow.
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This page was last updated on October 22nd, 2011