Saturday, April 13, 2013

The Cold April week

Updated with Saturday, April 13th stats

Fairbanks has chilled through the coldest April week since the 1920s. The average temperature Saturday, April 6th through Friday, April 12th was +2.6ºF. This is the coldest week wholly within April (no end-of-March days) since April 2-8, 1927, when the average temperature was also 2.6ºF. The coldest April week was in 1924, when the average temperature April 1-7 was -1.5ºF. If we include the last couple of days of March, then this is the coldest "mostly April" week since March 30-April 5, 1985, when the average temperature was 1.7ºF. This was not quite the coldest week so late in the season: April 7-13, 1911 had an average temperature of 1.0ºF.

Update: Saturday came in with a high of 25ºF and a low of -13ºF. So, the week of April 7-13th is now the coldest (and this should be the bottom), with an average temperature of +2.2ºF.  This the coldest April week since April 3-9, 1924, when the average temperature was +1.9ºF.  

The lowest temperature this week was 21 below on the 10th, the lowest April temperature since 1992. The only daily record temperature set was the low of 15 below on the 11th, which broke the previous record of 12 below set in 1936.

From my favored standardized anomaly viewpoint, the average daily temperature on Thursday, April 10 was 3.0 standard deviations below normal. This is the largest daily negative anomaly since June 4, 2006 (-3.4). However, this was only the absolute largest anomaly since May 28, 2011 (+3.1). A quick analysis of the weekly anomaly, using the full Weather Bureau/NWS era, 1930-2013 as a base comes to -2.9. This is no where close to the greatest negative weekly anomaly in April: April 20-26 1924 and 1948 both came in at -4.0.

Update: The average temperature of +2.2ºF for April 7-13 is 3.0 standard deviations below the 1930-2013 mean. 

How did this happen: cold low aloft. Here's the mean 500mb heights for April 6-12:
Courtesy NCEP/NCAR reanalysis
There have been no upper air records set or even approached. Rather, it's the duration of the cold pattern that has produced the cold April week.


  1. Here's my take on this cold...for some reason (and that should be identified) the upper air jet stream flow has recently forsaken Alaska. Until we get S-SW'll be colder than normal.

    Please explain the cause for the current flow, and there's the answer.

    It's more than a upper low...something created that low to begin with.


  2. Always appreciate your comments, Rick. Thanks for blogging.