“Washington State DOT reopened Rt 20, the North Cascades Highway for the summer. Apparently it’s one of the latest openings (May 25th)…”
And Chinook Pass Update from Washington State Dept. of Transport:
“Updated June 2, 2011
– WSDOT crews hopes to reopen Chinook Pass by the end of June.”
“What are the usual opening and closing dates?
In an average year, Chinook Pass closes in November and reopens in May.”
Washington State DoT has tabulated Mountain Pass Closure and Opening Dates:
In plotting the graph of openings, I left off the first opening date for the Cascades Highway – 02 September
1935 1972 – as I imagine that to be exceptional, perhaps surmounting unexpected challenges for the first time on the road in a reasonably heavy snowpack that year (Chinook Pass did not open until 22 June). [Update – reader ‘Gary’ emailed to point out my date error, saying: “You are correct to leave it out as I believe that it also had to do with the finishing the construction of the highway that year. 1972 was also a cool spring year with 2+ inches total of snow for the month at the Olympia Airport (elev. <200 feet).”]
Well it certainly looks as if there was an abrupt change from 1978. This coincides rather neatly with the shift in the Pacific Decadal Oscillation (PDO) to its warm phase in 1977.
If the snowpack and opening dates are correlated with the PDO shift, why does the earlier flip from warm to cold in 1946 fail to show up? I can only speculate that there is not enough data (1935-1945) for the eye to pick up a trend, or that road clearing was lower priority and probably still in its infancy as a regular state-wide service. Anyone know anything about how the efficiency of ploughing/plowing technology has changed since the 1930s? The equipment had been around for quite some time:
Well, it will be a few years before we see if there is any ‘flip’ back to greater snowpack and later openings, but then, if the cold PDO does bring more snow ‘on average’, economics will likely play a part these days – the pressure to get the roads open for commerce and the pressure on state budgets of doing so.