This winter the Interior had quite some snow. Actually, it was the most I have ever seen since I moved here in 2001. We not only had some strong snow storms this cold season, but some of them also came with quite some wind. Some of you may remember the photos of the snow pile blown in front of our garage door.
No wonder that this winter, the Steese Highway was closed at Eagle Summit for some time. This closure cut off the road access to Fairbanks to the people living north of this point. During that time, they depended on subsidence lifestyle, what they had in storage and supply flown in by small aircraft landing on skids.
In town (Fairbanks), the department of transportation worked 24/7 to remove snow. Along the roads and streets the snow was man-high in some places. They drove snow in trucks to places outside of the city limits. Out in college, where we live, the snow was about the height of the mailboxes. The big pile of snow that the snow plow piled up in our front yard is so high that one can barely see the driveway lights (see photo above). We even had to shovel a way to the tank as the pipe was totally hidden under the snow-pack.
The normal annual snowfall for the Fairbanks North Star Borough amounts 61.6 inches (156.464 cm). However, from a wildfire and hydrological point of view, it makes more sense to look at the water-year-to-date snowfall in the area. The water year starts October 1 and ends September 30 the following year. The dates are chosen with the idea that the soil is at its maximum moisture at that time a year. This water is assumed to be stored and available for the next vegetation season.
On March 19, the long-year normal water-year-to-date snowfall in the Fairbanks North Star Borough is 51.8 inches (131.572 cm). On that day, the area had already a water-year-to-date snowfall of 77.8 inches (197.612 cm) this year! This means 1.5 times the normal water-year-to-date snowfall!
Currently, the average undisturbed snow-depth is 29 inches (73.66 cm) in the area. The maximum snow depth so far was reached on February 26 with 34.1 inches (86.614 cm).
No there was no snow-melt between February 26 and March 19. This March was particularly cold. It seemed like someone had glued the needle at -25.6F (-32oC) even late in the morning. Of course, it got warmer during the day, but still, one had to bundle up and wear some extra layers. This March took a good try at confirming the old 1959 Johnny Horton song “When it’s Springtime in Alaska, it’s Forty Below.” 😉
The thickness of the snow-pack decreased by snow metamorphism. Some of it is related to settling due to gravity. Another part is due to water vapor transfer within the snow-pack. The saturation water vapor pressure over a concave surface is less than over a plain surface, which itself has a lower water vapor pressure at saturation than a convex surface. Thus, the sharp edges of snowflakes sublimate already at water vapor pressures that still allow water vapor to deposit on concave surfaces. Consequently, dendrite-like crystals morph into hexagonal plates and eventually, at the end of the snow season, into ice spheres of about two mm (~0.08 inches) in diameter. During this process the density of the snow increases for which its volume and hence depth decrease. Remember, density is mass per volume.
On days when the water vapor pressure is below the water vapor pressure of a concave surface, the thickness of the snow-pack decreases by sublimation of snow at the surface. This process, of course, increases the water vapor gradient within the snow-pack leading to water vapor fluxes, snow metamorphism in the snow-pack as well. Furthermore, water vapor is transferred to the atmosphere thereby increasing relative humidity. In cold calm nights, this process may lead to fog close to the snow surface. Looking at the above diagram, one sees that March’s relative humidity was low, which means sublimation of snow occurred.
Note that on climatological average, March is the driest month of the year in the Interior with respect to precipitation (see diagram above) and cloudiness. Thus, March provides the best chances to watch the aurora.
How was your winter so far? What was the snow situation this winter where you live? How deep was the snow? Do you still have snow? Has spring arrived already?
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Dingman, S.L. (2021) Physical Hydrology. 3rd edition. Prentice Hall.
Fröhlich,K., Mölders, N. (2002) Investigations on the impact of explicitly predicted snow metamorphism on the microclimate simulated by a meso-β/γ-scale non-hydrostatic model. Atmospheric Research, 62, 71-109, doi:10.1016/S0169-8095(2)900005-4.
Photos of me: G. Kramm
Photos of snow and diagrams: N. Mölders
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