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[pct-l] Sierra snow plot



I've got a sneaky new plot that "predicts" Sierra snow levels.

    http://theory.lcs.mit.edu/~e_lehman/utyplot.png

This is not your typical snow graph, so let me explain...

* The Y-axis indicates the snow level measured by a sensor at Upper
Tyndall Creek, which is at 11400' and pretty close to Forester Pass.

* The X-axis measures days relative to "Ray Day", June 15.  So the plot
runs from about four months before to one month after Ray Day.

* On the left side of the graph, there is a single red line.  This is the
actual snow level at Upper Tyndall Creek this year-- 2005.  Of course, the
red line ends today (April 2).

The remainder of the graph is a big mass of multicolored lines.  I know
some are difficult to distinguish, but this is the sneaky part.

Today, the snow water equivalent at Upper Tyndall Creek is 38.7 inches.
Suppose that in each previous year on this date-- April 2--- someone had
hiked up to the snow sensor with a shovel and either piled on more snow or
shoveled off some snow so that there was exactly 38.7 inches-- just like
today.  The graph shows how the meltoff would have proceeded from that
"corrected" snow level.

Looked at another way, the graph show what will happen THIS YEAR if our
meltoff pattern matches a previous year.  So that mass of colored lines
represents the "envelope of uncertainty".  The snow level for the
remainder of the year is almost surely going to run somewhere through that
big tangle.

For example, one dark blue line on the graph plunges to zero before Ray
Day.  So if the melt pattern this year follows the melt pattern that year,
Upper Tyndall Creek will be bare of snow well before June 15.  (This area
actually was snow-free by Ray Day in about 2/3 of the years from
1970-2004-- so that's something to hope for!)

Below the dark blue line, there is a pink line which drops very fast, but
never makes it down to zero.  In that year (1981), the meltoff was
super-fast.  However, on April 2, 1981 there were only 16.0 inches of snow
at Upper Tyndall Creek.  So the pink line ends after only 16.0 inches of
meltoff.

On the other hand, there have been several years where Upper Tyndall Creek
didn't drop 38.7 inches below the April 2 level until a *month* after Ray
Day.  The corresponding lines run into the lower right corner of the
graph.

I'll update this graph from time to time, if I remember.  (If you're
curious, send me a reminder and I'll do it.)  With each passing day, the
"envelope of uncertainly" will grow smaller...

/Eric

P.S.  Actual snow levels for 1970-2005 are plotted here:

  http://theory.lcs.mit.edu/~e_lehman/utyplot_abs.png

The flat lines followed by jumps that appear in some years are due to
sensor outages.