The widespread cold of the last week in Alaska has been really exceptional for this late in the winter. Only a quick glance at UAF's statewide temperature index is needed to confirm this - see the chart below. The index has been nearly pegged at the bottom of the scale since last Wednesday.
Recall that the index scale is designed to indicate the departure from normal in terms of frequency, so an index value near -10 corresponds to near-record cold for the time of year (compared to the 1991-2020 climate).
The calculation behind the UAF index is actually the average standardized temperature anomaly across 25 observing sites, taking into account the reduced climatological variance at more maritime locations and the greater variance in the interior. Last Friday (Feb 27), the average anomaly was 3.1 standard deviations below normal, which is the lowest daily value since the remarkable cold snap of April 2021. Prior to that, the only dates in the past 20 years with such anomalous statewide cold were in April and May 2013 - the year of the record late breakup at Nenana.
If we only look at December through February, it's interesting to note that only ONE other event since 1991 produced a daily statewide anomaly below -3 SD, and that was early February 1999. The cold back in December and early January this winter didn't reach anywhere near the same intensity, peaking at only 2.3 SD below normal on January 3 (the persistence of the cold was a more unusual aspect on a statewide basis).
Therefore in the context of normal Alaska climate at the end of February, the last week has been very extreme, a rare cold outlier.
Fairbanks exemplifies this: the low temperature of -49°F on Sunday was the coldest in March since 1911, and it tied the monthly record for the 1930-present era. It's also the first time since 1932 that 5 consecutive nights have dropped below -45°F after mid-February. In fact, until this winter such a string of cold nights hadn't happened at all since the New Year's cold snap of 1999-2000.
More on this winter's achievements in Fairbanks in a subsequent post.
