Snow depth and snow water equivalent measurements along a road course and historic snow course in the Andrews Experimental Forest, 1978 to present

CREATOR(S): Alfred B. Levno, Mark D Schulze, Greg Downing
PRINCIPAL INVESTIGATOR(S): Mark D Schulze, Sherri L. Johnson
ORIGINATOR(S): Alfred B. Levno
OTHER RESEARCHER(S): Greg Downing, Benjamin Nash, Suzanne M. Remillard, Christopher Daly, Stephanie A Schmidt, Adam M Kennedy
ABSTRACTOR: Donald L. Henshaw
METHOD CONTACT: Greg Downing, Benjamin Nash
FORMER INVESTIGATOR: Don Henshaw, Frederick A. Bierlmaier, John Moreau, Anne W. Nolin, Adam B. Mazurkiewicz
12 Nov 2004
30 Jun 2023
hydrology, climatology, microclimate, precipitation, snow water equivalence, snow depth, reference stands, forest management, modeling, canopy gaps
Provide a baseline for characterizing distribution and variation in snow depth, moisture, and duration in the H.J. Andrews Experimental Forest for climatological and hydrological analyses and modelling and to examine differences in snow accumulation in clearcut and adjacent closed forest stands.
Experimental Design - MS007:
Description: Snow stakes were established starting at the Primary Met Station (430 meters elevation) and at approximately 150 meter elevation increments along Andrews Forest roads. Sites are established in open canopy/closed forest pairs, with stakes at each paired location as close together as possible. One stake is placed in a forest opening (no canopy interference with snow accumulation) and one stake is placed in an older forest (preferably an old growth stand). Before snow year 2015 that starts in fall 2014, observations of snow depth were made in person and not on any schedule. Since fall 2014, daily depths of snow in the vicinity of the snow stake are recorded from camera images. Snow water equivalent measurements (snow moisture content) are collected once or twice per year with 3 snow cores taken in the vicinity of the snow stake and averaged. The historic Reference Stand snow course included paired open and closed canopy locations within the Andrews Reference Stands and Wildcat RNA thermograph sites.
Field Methods - MS007: Road snow course :

A snow stake is established at each site with a metal fence post driven into the ground to support a 2" PVC pipe that slides over the post. Survey rod decals are placed on most of the PVC pipes except at lower elevation sites where shorter stakes are adequate and stream level metal guys are used as the calibration system. Slope and aspect are recorded for all sites, as well as the initial stake tare reading relative to the ground (not all stakes have zero at the ground level).

Before 2014, depth measurements at the stake were recorded, and high and low depth values were visually estimated only. These data were routinely recorded at the stakes while driving to other field activities. Typically, the Upper Lookout stakes on Rd. 1506 and Rd. 350 stakes were read once every 3 weeks. The 1507 stakes were sampled only once or twice a year. A check sheet was established to keep the collected field data organized.

In 2014, timelapse cameras (mounted on trees with a small overhanging shelter) were tested to capture daily images of the snow stakes. In 2015, they were deployed at all snow stake locations as the primary means of data collection, but not replacing in-person site visits and data collection with check sheets. The cameras are set up to capture 3 images a day at 09:00, 12:00, and 15:00 PST. One of the three images, usually 12:00 by default, is interpreted later during data entry for snow depth and snow cover.

A special trip is also made at least once per year to collect snow water equivalent (SWE) measurements as a way of ground truthing the snow in the vicinity of the stake for snow moisture. The nearby snow stake is measured at the same time. SWE Measurements at each stake are conducted by taking three snow core measurements with the Mt. Rose or “federal” snow tube sampling equipment to establish a relationship between snowpack water equivalence and depth. The snow tube core sampler is pushed down to the soil surface interface, depth is recorded, and snow is extracted. The snow core is measured, any soil plug removed, and the core weighed on a spring balance, with the tare weight of the corer subtracted, and the actual snow weight is converted to millimeters of equivalent water.

The snow tube sampling procedure generally follows the NRCS snow sampling procedure except only three cores are taken. If there is a complete snowpack around the snow stake, 3 points are taken in the immediate vicinity of the snow stake (3 points approximately 1 meter equidistant from stake) and averaged. If the snow coverage is patchy, core sample placement becomes more subjective with limited spots where a useful core can be sampled. In the NRCS snow course a particular point not having any snow would be recorded as zero, but here all of our ground truthing cores have some amount of snow because points are selected for representation of the density of the snow (and not for representative depth). The % snow cover is estimated from camera images to document snow patchiness.


Mt. Rose or “federal” snow core sampler. Note that a new snow core sampler was put into use on approximately March 1, 1999. The new scale can measure greater weights. Generally, comparable snow cores weigh less on the new scale in comparison to the older one.

Wingscapes timelapse cameras, including Birdcam Pro WCB-00019 and TimelapseCam Pro WCT-00121, WCT-00122, and WCT-00126 with SD card and C or AA batteries, depending on the model.

Field Methods - MS007: Reference Stand snow course:
Description: At each site, snow is sampled at 10 points along a transect at 5 meter intervals. In 1988 the number of points was reduced to 5 per site. The snow tube core sampler is pushed to soil surface interface, depth is recorded, and snow is extracted. The length of the snow core is measured as an indicator of snow compaction. The snow is weighed on a spring balance, the tare weight of the corer is subtracted, and actual snow weight is converted to inches of equivalent water. In Reference Stands 4,12,13,14 paired transects in closed forest and open areas are taken. An open site was added at RS03 and RS26 for 1 year (WY90). At RS04, the open canopy site was moved to the road beginning WY91. Throughout the 1990's only RS04 and Wildcat RNA sites (RS13, RS14 open-closed canopy pairs) are measured, and only RS13 and RS14 after 2000. These measurement s were discontinued in 2003.
Instrumentation: Mt. Rose or “federal” snow core sampler.
Processing Procedures - MS007:
Description: The cameras are removed from the field at the end of the snow season (usually May). The files are downloaded to directories by snow year and stake (sitecode). An in-house C# program was written to allow a person to review and record data from each image. Data then undergo a suite of QA/QC procedures. The data are converted to metric units and flags are applied.
Quality Assurance - MS007:

The time-lapse cameras are removed every summer (usually May) and reinstalled in fall (usually November), and because of this, the exact orientation of the cameras differs slightly from year to year. Efforts are made annually to maintain the snow stake sites, such as clearing vegetation, trimming low branches, etc., but there is always some environmental variability. A few stakes have been moved, which is indicated by the position attribute in the data.

To ensure quality data, those assessing data in the field and processing snow stake images are trained by more experienced personnel and given guidance on visual interpretation and data entry. However, with assistance from a variety of personnel over the years, the human factor in interpretation, the difficulty in assessing percent cover from a vertical camera, the limits of equipment in winter conditions, and uncontrollable environmental variables, there is a degree of imprecision in the data that should be acknowledged.

After data entry, there is a stepwise review that occurs on both the data entered online and through spreadsheets and programs by data managers and field personnel. The data is flagged and corrected for issues such as mistakes and typos, illogical values, and inconsistencies. The entry notes are also used to help flag data appropriately. The snow depth is eventually converted to metric units and made available. The snow images and data sheets are also archived.

Data Entry - MS007:

The snow stake data from the field check sheets were originally entered into a spreadsheet. An in-house C# program was developed to make image interpretation and data entry easier for a quantity of images that can exceed 20,000 in each season. This program is used for sequencing images and entry from the field check sheets. Depth is entered in increments of 0.1 foot, and non-zero values less than 0.05 feet are interpreted as a ‘trace’ amount of snow. In some cases, high and low depths were estimated from the images as well, but this was discontinued following snow year 2017 due to its difficulty and low confidence in the numbers produced.

Snow cover is considered only for the relevant open or closed canopy areas with consideration for site specific factors such as vegetation, roads, tracks from vehicles, field of view, camera angle and height, and “stake” well or mound. For example, the snow stake can accelerate melting (e.g. albedo effect), which creates a depression around the stake (i.e. “stake” well), or through wind, can cause a small snowdrift or snow to mound up around the stake, issues which are accounted for by assessing the area around the stake to compensate for its effects. Data obtained from blurry or obscured images (with variability in megapixels between camera models) is sometimes inferred when reasonable and flagged as Q (questionable or estimated) and left blank when not able to read.

The historic Reference Stand snow course was conducted throughout the 1980's and 1990's. The first measurement listed for a year is generally the first measurable snow of that year. However, the data suffers from not knowing the difference between no snow on the ground and no measurement of snow which makes the determination of snow melt-off difficult or impossible. Reference Stands with some snow measurements include RS03, RS04, RS05, RS12, RS13, RS14, RS18, RS26, and TS38. After 1993 only data from RS04 and two reference stands from the Wildcat RNA (RS13, RS14) are collected.
Measurement sites include recent clearcuts and adjacent old-growth stands in the H. J. Andrews and vicinity from Reference Stands at 430 -1450 meter elevation, and include two open-forest paired sites in the Wildcat Research Natural Area.
The current snow course includes old-growth stands and adjacent open areas along the road network within the H. J. Andrews Experimental Forest of the western Oregon Cascades. The historic snow course survey includes some Andrews Reference Stands and Wildcat RNA sites.
Ground condition