Anchorage

December 2011 destined for Anchorage weather folklore

Five remarkable windstorms walloped Alaska's largest city during December, including one that spanked Glen Alps entrance to Chugach State Park with a 118-mph gust -- "about as high as any since the wind sensor has been installed," says a new analysis posted by the National Weather Service in Anchorage.

December "will go down in local weather lore as one of the windiest months on record," wrote meteorologists John Papineau and Emily Niebuhr in the report.

"The rapid succession of these storms as well as the occurrence of significant amounts of snow and rain have made this December one to remember or forget depending on one's experiences over the past two and half weeks with fallen trees, extended power outages, damaged roofs, blown down signs and icy roads."

These five big wind "events" (which might be the official weather scientist term for "wild-ass storm") struck Anchorage during a 18-day period between Dec. 3 and Dec. 21. Four of the storms were "chinooks," where dry and warming air flushes down the Chugach Mountains front and slobbers all over the Anchorage Bowl with temperatures that temporarily rise into upper 40s and lower 50s.

The paper -- titled "Wet, Windy and Wild" -- contains a summary of each of the five storms, what was strange about them, and tries to explain how Anchorage's unique geography conspires with the Pacific storm track to produce such startling horizontal weather.

In general, these "downsloping events" occur when big low pressure systems roil into the Bristol Bay region while high pressure builds to the east, often in the Gulf of Alaska, they explained. Wind then rushes from the high toward the low, flowing over the top and down the face of the Chugach Mountains, and accelerating through the narrow gaps of Portage Pass and Turnagain Arm.

But there are mysteries -- "finer details that still elude forecasters," the two scientists wrote here:

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For other explainers and research about Anchorage weather, check out the Weather Classroom.

Contact Doug O'Harra at doug(at)alaskadispatch.com

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