Tuesday, April 28, 2015

Melt-Out Progress

The valley-level snowpack melted out to a trace 10 days ago in Fairbanks, but higher elevations near Fairbanks still have a significant depth of snow on the ground, as do many other interior locations.  The photos below were taken at about 6pm AKDT yesterday on Keystone Ridge; the snow depth measurement was 13 inches.

It's a little unusual to have this amount of snow left on the hill 10 days after valley-level melt-out, as the normal difference in melt-out dates is 11 days.  In the 18-year history of the station, only 3 years saw more snow surviving 10 days after valley melt-out.  This year's anomaly appears to be related to the warm - but not excessively warm - chinook pattern, which efficiently removed the valley-level snowpack but has not become warm enough to cause rapid melting at elevation.  Through yesterday, April 2015 is the 11th warmest April since 1930 in Fairbanks.

The list below shows the most recent snow depth measurements from various first-order and SNOTEL sites across interior and western Alaska.  If a date is included in parentheses, it indicates the 1981-2010 median melt-out date. 

Fort Yukon SNOTEL  0" as of today
Coldfoot SNOTEL  17" (May 15)
Atigun Pass SNOTEL  41"
Bettles SNOTEL  16" (May 16)
Bettles airport  10" (May 12)
Kotzebue  3"  (May 20)
Nome  4"  (May 12)
McGrath  0" (melt-out April 11, median May 4)
Eagle COOP  10" 0" (observer error reported 10" in recent days) (May 1)
Chicken COOP  4" (1997-2014 median May 1)
Granite Creek SNOTEL near Delta Junction  6" (April 27)

Other SNOTEL sites:
Little Chena Ridge 2000'  8"  (May 7)
Upper Nome Creek 2520'  23"
Upper Chena 2850'  34"
Munson Ridge 3100'  31"  (May 26)
Eagle Summit 3650'  18"


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  2. To correlate with the slower melting in other areas, the rivers aren't rising as fast as they normally would. Monday afternoon I noticed that the Chena near the airport started to pick up speed but didn't have a huge rise. And the amount of broken ice in the river is smaller than last year. I'm not complaining; this means less chance of flooding within town.

    Perhaps you could look at the various river gauge heights and compare them to where they normally would be and how fast they normally rise during breakup?

    And is there anyway to estimate how much snow we would have without Chinooks melting it away? Would the Nenana have gone out much later than it did?

    Thanks, Richard, for your posts on this blog.

    1. Eric, good observation - slower melt in the hills means slower river rises. It would be an interesting project to correlate river rises to temperatures and snowpack diminution, but I don't have the gauge data at my finger tips just now.

      The rapid valley melt-out may have pushed the ice out at Nenana a bit earlier than otherwise, but this is a difficult multivariate problem because there are so many other factors such as thickness and integrity of the winter's ice and local rates of melting from sun and warmth. It's difficult to isolate the influence of any one variable. But there's no doubt the breakup was early considering that temperatures were not that high.

    2. Downstream of the Tripod is the tributary Nenana River. If it flushed out then there's not much stopping the flow immediately upstream adjacent to the city of Nenana.


    3. Here is a good starting place for downtown Chena river depth and discharge data: http://waterdata.usgs.gov/nwis/inventory/?site_no=15514000&agency_cd=USGS. I haven't checked out the possible download file format.