Friday, April 15, 2011

A Tale of Two Springs

Chances are you've read the press coverage with regards to the potential flooding this spring.  The snowpack is our biggest reservoir, and yes, there is quite a bit up there waiting to let gravity take over.

How things play this spring out depends on a number of factors, some of which are related to the snow (e.g., is it dirty from dust storms), some of which are related to the soil (e.g., how saturated they are), and some of which are related to the spring weather.  We'll talk about the latter here.

There have been a number of comparisons to 1982-83 when in late May and early June City Creek famously flooded down State Street.  The best way to commute to downtown that year was by kayak.

Source: Wikipedia Commons/US Government
Although it is not in the City Creek drainage, I'm going to use the Ben Lomond snotel here to take a look at where things currently stand and show two scenarios that perhaps represent the extremes of what could happen from here.  At the moment, the Ben Lomond snotel is measuring about 58 inches of snow water equivalent (SWE, green line).  This is 136% of average (other snotels are much higher than that) and remarkably similar to the snow water equivalent observed on this day in 1983 (red), but also 1998 (light blue).

Source: NOAA/NWS and NRCS
I have picked 1983 and 1998 because those two years follow dramatically different trajectories with regards to the spring snowpack evolution.  In 1983, it continued to snow and the snowpack did not peak until just after mid May.  Then, mother nature flicked the switch, it warmed dramatically, and the entire snowpack melted rapidly in a span of about 4 weeks.  Impressive.

In 1998, the snowpack peaked in mid-April and then began to decline.  So, the peak was lower, as was the rate of snowpack decline, which spanned a period of about 2 months.  This is the tale of two springs and what makes streamflow predictions difficult.  We have a lot of snow, but how things play out and just how serious the flooding is will depend on the whims of Mother Nature over the next few weeks.

Of course, the snowpack may be a boon for spring skiing.  The Lookout Peak snotel near the head of City Creek Canyon is just over 200% of average.  I'm thinking this could be a good year to plan a spring corn skiing trip there.

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