January 14, 2011

Chinook Winds + January Thaw - Hits the PNW

This evening, our driveway was void of snow for the first time since November.  The temps in Spokane for the past two days and for the next couple will be near 40 degrees.  Last week it didn't get above 17.

We have two phenomenons to thank:

1) The January Thaw:
  • January thaw, is a climatic phenomenon of unseasonably warm weather that tends to occur at about the same time every year, usually within about 10 days after the middle of January. Generally, the January thaw is gradual and temporary, lasting anywhere from a few hours to a week
  • The causes of the January thaw are known. General atmospheric circulation becomes more westerly, or even southwesterly, and mild Pacific air spreads eastward across Canada. The stronger-than-normal westerlies in mid latitudes tend to confine Arctic air northward and favour the intrusion of warm, humid air from the subtropics into the eastern US and Canada. Although the westerly flow may last several days, it inevitably shifts to northwesterly, again allowing cold outbreaks of Arctic air to stream southward and eastward.
  • Still a mystery, though, is why this phenomenon occurs when it does. Some researchers offer statistical evidence for a relationship between January thaws and sunspot activity.
2) Chinook Winds
  • The reference to a wind or weather system, simply "a Chinook", originally meaning a warming wind from the ocean into the interior regions of the Pacific Northwest.  A strong Chinook can make snow one foot deep almost vanish in one day. The snow partly melts and partly evaporates in the dry wind. Chinook winds have been observed to raise winter temperature, often from below −20°C to as high as 10°C to 20°C.  

There are too many red flags out there right now!  What does this mean for us?  A study/relax weekend :(


Red Flags:
  • 75 mph winds reported in the southern Selkirk's of northern Idaho today = massive wind slabs being formed on a layer a couple of feet thick of upside down snow deposited on surface hoar and facets formed earlier this week, not to mention persistent weak layers deeper in the snow pack.
  • heavy wet snow falling on top of a dry cold snow pack = a non-supportive very reactive interface between the two layers
  • my pit results from 6000' on 1/9/2011 revealed and confirmed two different faceted weak layers,  these weak layers were not very reactive but present.  With the load from the heavy snow on top, these weak layers will surly play a roll and possible encourage a slide to step down into the Dec 13 rain crust that still persists.   
Location:Palmer creek
Date: Jan 12th, 2011
Photographer:Kevin Wright
Description: 01/07/2010 avalanche event. Skier triggered, full burial. No
injuries. Investigation showed the initial weak layer as buried
surface hoar with weak facets, stepping down to facets above and
below the November 22 rain crust. Deeper parts of the crown face
were on top of the rain crust


The GOOD news...The powder will come back.  This cycle should be good for stability in the long term....if not back to CANADA:)