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| Notes on snowpack data:
This report is condensed, I have not included all data sites. Therefore the Basin Wide % of Average figures may not calculate as you would expect them to due to the inclusion of data sites which I have not listed here. However, the figures are correct.
The reference period for average conditions is 1961-1990.
This report is based on Natural Resources Conservation Service data.
Interpreting the data:
While total precipitation is the standard by which we typically gauge snowpack levels and how they will effect stream flows, Snow-Water Equivalent is arguably a better measure. Keep in mind that lots of strange things can still happen. Though percentages are high for this time of year, spring weather patterns will largely determine when the rivers will clear enough for fishing.
As of February 2, we are on the verge or perhaps have already surpassed the average winter snowfall. Precautionary measures are being taken in Jackson Hole due to the possibility of a major runoff.
How will this effect the fishing? With the increase in dam releases which have already begun we are getting better than normal winter flows in the rivers and the trout are the beneficiaries. With the exception of the dams and levees, the single most limiting factor in the health of our trout population are low winter flows. It wasn't a problem last year and it appears it won't be a problem this year either.
The February 16 report indicates two weeks of relatively dry weather and a significant drop of roughly 15% for snow-water precipitation across the board. Personally, I wouldn't mind seeing this trend continue.
As of March 2 we see the drying trend continue as we experience another approximately 10% drop in snow-water equivalent since February 16. In the past four weeks there has been a 25% reduction in the snow-water equivalent of the snowpack.
Between March 2 and March 16 we received minor periodic snowfalls, yet the snow-water equivalent still managed to drop slightly at almost all data sites. Brisk, sometimes warm, winds throughout this time period undoubtably helped offset the precipitation we received.
From March 16 through the 30th we actually saw some increases in the average precipitation. The snow-water equivalents however, continued to creep lower. Nonetheless, the Snake River still has about 20% higher snow-water equivalents than this time last year.
As of April 13, cool weather and additional snowfall has allowed the snowpack to maintain it's status quo as little has changed for the past six weeks. This is bad news for those who have built homes in the Snake River's flood plain.
A recent storm which passed through the area has once again bumped up the snow-water equivalent as of April 27, particularly in some of the drainages which feed directly into Jackson Hole.
On May 9 and 10, the Snake River began to turn significantly off color. While it's not yet the color of chocolate milk, it is a very dirty green. Cool nights are preventing heavy runoff at this time, but runoff has begun nonetheless.
The figures for June 1 show a dramatic reduction in the snow-water equivalent of the snowpack. This was a result of two weeks of unseasonably warm May weather. The past week however, has seen a significant amount of rainfall which, if it continues, could lead to storage problems in Jackson Lake.
Guy Turck
gturck@compuserve.com
Last updated: June 1, 1997
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