Frequently Asked Questions - Definitions/Terminology
Additional FAQs
- What is a drainage basin?
- What are quartiles and how are they related to flows, water storage and snow water equivalent?
- What is snow water content (snow water equivalent)? How is this different from snow depth?
- What is a snow pillow?
- What is a snow course?
- What is the difference between snow pillow and snow course data?
- What is meant by water year?
- What is meant by water mastering?
Q. | What are quartiles and how are they related to flows, water storage and snow water equivalent? |
A. |
Quartiles are three values which divide sorted data sets into four (approximately) equal parts. The lower quartile (1st quartile) is the value that separates the bottom ¼ of a dataset from the remaining top ¾ of the dataset. The second quartile (median) is that value that divides the dataset into two equal parts such that 50% of the values are lower and 50% of the values are higher than the median (2nd quartile). The upper quartile (3rd quartile) is that value that separates the upper ¼ of a dataset from the bottom ¾ of a dataset. Quartiles are used to show the "normal range" of data (band between the lower and upper quartiles) for flows, water storage and snow water equivalent (pillow data). See also Water Supply Outlook and how normal is applied in the Water Supply Outlook. Note that the median for our flow and pillow datasets is termed the average. The median and average for most of our datasets are very close given the large numbers of data points within our datasets. |
Q. | What is a snow pillow? |
A. |
A
snow pillow is an a automated set of apparatus that measures, records and transmits snow water equivalent.
from a remote site to an office or laboratory equipped to receive such information. Precipitation and temperature gauges are usually part of the total installation. |
Q. | What is the difference between snow pillow and snow course data? |
A. | Snow water equivalent values on the snow pillow may or may not match the snow course value at a particular location. While snow pillow data is very valuable information, the quantity of snow on the pillow is only representative of the accumulation at that specific spot. A snow course survey is measured at numerous spots and provides a more representative value of snow in the area. In some locations, there can be considerable difference between the snow pillow and snow course values. Factors such as wind and exposure of the site can cause the snow pillow values to be significantly different from the snow course survey. The snow pillow graphs on our Web/site show the daily average snow water equivalent. The monthly snow survey is the average of all measurements conducted within five days of the end of the month. Also, where snow pillow and snow course measurements are available for the same site, snow pillow records tend to be much shorter (10-15 years) in length compared to the snow course sites. As a result, the difference in the average value between the snow pillow and the snow course can be attributed to snow water equivalent being derived two different ways (physically measured compared to an instrument reading), site location and length of data record. In some cases, the values can deviate by 10-20%. Therefore, while snow pillows are excellent for analyzing trends and for monitoring accumulation between snow surveys, snow course values should always be used when considering the quantity of snow at a particular location as they best represent that area. |