Panorama by Robert Woolsey, KCAW
More snow over the weekend brought Sitka’s total snowfall for November to over 32 inches – a modern record for the month.
The previous snowiest November was in 1990, when 30.7 inches fell. Municipal building official William Stortz remembers it well.
“It was twenty years ago. It came with the house we bought, one of those little metal Sears & Roebuck kit sheds. You’d screw them together. It pretty well was flattened.”
The National Weather Service on Monday (11-28-11) issued a special weather statement advising area residents – particularly in the northern panhandle – to be alert for increased avalanche danger and heavy structural snow loads as temperatures warm up this week. Heavy rainfall forecast for Wednesday and Thursday is expected to soak the already deep snow.
Stortz says there are too many variables, such as insulation, roof pitch, and roofing material, to predict which buildings are vulnerable during heavy snowloads. He’s noticed considerable differences in how much snow local buildings are carrying, just since temperatures began to warm up Sunday evening. Older, less well-insulated structures, he says, are already losing much of their snow loads to melting. Newer buildings are holding more snow, but he says they are generally built to a higher standard.
“Newer construction is designed – hopefully, if there was a truss manufacturer or a structural designer involved – to hold a specific snow load, and it’s all calculated for the area in which we live. So I would think that if a place was built to code and built to current design standards it should be safe enough for this concern about this excess rain falling on existing snow on a roof.”
Stortz thinks some greenhouses or other outbuildings – like his former metal shed – may be most at risk since they’re unheated and typically not designed to carry roof loads.
Consistent snowfall records in Sitka only go back as far as 1948. And while 32 inches sounds like a lot, it is by no means Sitka’s snowiest month. That happened in December, 1961, when 40 inches fell.
Additionally, these are sea level records. Alpine conditions in Sitka are much different. The snowpack on the Gavan Ridge measured at 53 inches on Sunday afternoon. That’s more than the 44 inches reported at the base of the Eaglecrest ski area in Juneau.
All this snow could be useful next summer toward replenishing Sitka’s hydroelectric reservoirs, which failed to reach spill level this fall. In 2007, when the spring snowpack measured a staggering 12-feet deep above town, a Forest Service hydrologist calculated that the snow contained about 30-percent water.
If that water percentage holds true for this November’s snow, the rainfall equivalent the alpine snowpack at present is 15 inches – exactly the amount of Sitka’s rainfall shortage for 2011.