Low-Elevation Sunshine

Colder than normal conditions have settled over the interior, and so far the RAWS thermometers at Norutak Lake and at Prospect Creek/Jim River have measured the coldest conditions: -45°F this morning.  A report of -49°F from the Bettles SNOTEL site seems suspect as that site always runs cold.

Norutak Lake is located just north of the Arctic Circle and just to the east of the upper Kobuk River where it drains south out of the Brooks Range.

It is interesting to note that yesterday's hourly temperature observations from Norutak Lake showed a rise of 8°F in association with some very weak solar radiation during the day (see below).

 

The sun only rose to an elevation of 2° above the horizon yesterday at Norutak Lake, so I wouldn't have expected to see such a large diurnal temperature change.  However, a closer look at the topographic map reveals that the RAWS site is located on a south-facing slope at the north side of the lake.  The RAWS elevation is given as 800', but Norutak Lake itself is at 712', so the thermometer is almost 100' above lake level.  It seems that the south-facing exposure allowed for a bit more solar heating than would occur at lake level, and the daytime warming may even reflect the warm bias that RAWS thermometers are known to encounter on calm, sunny days.

With a surface-based temperature inversion undoubtedly in place over Norutak Lake, it's likely that temperatures near the lake surface were at least a couple of degrees lower than at the RAWS site, and perhaps substantially lower.  At Fairbanks airport it is normal to see an inversion of 4-5°F per 100 feet at the surface during winter, and 10°F per 100 feet is not uncommon.