Trego's Mountain Ear

As a young man, I never thought that working snow surveys would prepare me for a career in demography – but populations are populations, whether of snowflakes or humans (and some humans are definitely snowflakes). When you’re dealing with populations, you don’t make predictions, you make projections – you project the line of the curve, adjusting for variables. This chart, taken this morning from the station at Stahl Peak, illustrates why projecting snow pack from the January 1 measurements is asking to be found in error. It’s not a lot different from projecting populations in counties that are at the edges of the bell curve – whether losing or gaining.

Looking at the jagged black line on the left, we see that by mid-December, the snowfall was significantly above the average and the mean, but by the first week of January had pretty much reached its peak. By February 1, it was slightly above average. My guess – and it is more guess than scientific – is that by March 1, we will be seeing the line drop below the 30 year median – and only some surprising late season snows will maintain a ‘normal’ set of winter measurements.

If you look at the curve, you will notice that it is not the classic bell curve – it is a skewed curve. Many curves are skewed – if we look at longevity, a couple centuries back, there was a huge death rate between 0 and 5 – infants and children died like flies. Along with improved medicine and drugs like penicillin, the skew on the left disappeared – but projections became no easier. The graph below, showing age of death at different times in our history shows a chart dramatically skewed to the left:

The next chart – this time in bar graphs – shows the changes in death rates, by age, as improved medicine and health care became the new normal. Note how the NICU units and improved maternal health care of 2009 have changed things since 1900.

So it would take a braver man than I to project February’s snowpack winding up as normal – my feel is that, if we get by to March without a significant event, we’re looking at a dry year. But I’m not arriving at that guess by projecting the line.