The 500mb analysis from yesterday afternoon helps reveal the reason for the unusual conditions: see below (click to enlarge). The cold trough aloft is deeply entrenched over the western half of Alaska, and Fairbanks is under a zone of strong temperature gradient aloft with southerly flow; notice the tightly-packed dashed lines over the southern and eastern interior, denoting a tight gradient between very cold air over western Alaska and much warmer air to the east. (The dashed lines indicate 1000-500mb thickness, a good measure of overall temperatures in the lower troposphere.) Cold air is reaching Fairbanks from the base of the trough, but the frontal zone is proving a lifting mechanism to generate clouds and snow.
If and when the frontal zone shifts east and clouds clear out, temperatures will drop sharply in Fairbanks; most of the western interior is cold this morning.
On a related note, there were a few comments the other day about the variability of surface temperatures during cold spells like the current one. It's an interesting question as to whether surface temperatures are more or less variable when upper-air temperatures are low, so I looked at this by calculating the standardized anomaly of daily minimum temperatures for days in November through March since 1981; the chart below shows the relationship to 850mb temperature. (The standardized anomaly is the departure from normal, divided by the climatological standard deviation; both the normal temperature and the standard deviation vary greatly by date.)
The chart shows a hint that surface minimum temperatures tend to be less variable when the upper-air temperatures are low; for example, with very low 850mb temperatures below -30°C, the surface minimum temperatures mostly fall in the range of 0.5-2.5 standard deviations below normal. However, with very warm 850mb temperatures above freezing, daily minimum temperatures can be below normal or as high as 3 SD above normal.
The decreased variability during cold spells is seen in the chart below, which shows the standard deviation of the daily surface temperature anomalies in categories of 850mb temperature. The relationship is more noticeable for daily low temperatures than for high temperatures, which is why I used low temperatures in the scatter plot above. The results certainly confirm reader Gary's comment that "with 850 mb temps forecast to be -30 or below there's not a lot of room for variance in cold at the surface"; and I think this is because troughs of very cold air aloft are not generally conducive to very large temperature inversions near the surface.
