The warmer weather the last few days marked the end of an unusual stretch of below average temperatures that dated back to the last week of November. In a span covering nearly ten weeks, only two days surpassed the forty degree mark.
To better understand how this cold winter stacks up to those of by-gone years, it might be interesting to look back at the long term winter trends in this part of Pennsylvania. After the snowy winter we experienced last year, we took a similar look back at snow events and found that, while last year was snowier than average, it was certainly not the worst of our winters. Similarly, while this past one was cold, we’ll see that there have been many that were much worse.
We will define our unusually cold winters by tallying below zero temperatures. There are other ways to measure the severity of a winter, most notably the overall average temperature. The number of below-zero nights, however, is a good way to measure those extremely cold snaps that can cause heating costs to sky-rocket and even sometimes endanger lives.
This time in February is typically the last gasp for that extremely cold weather. Only five winters since 1925 have had a below zero day after February 21. Two of those three years, 1934 and 1963, were arguably our two coldest winters on record and the chill persisted well past the typical end of the frigid weather.
The winters of 1933-34 and 1962-63 were the only two in the last 85 years to have more than a dozen below zero nights. Our two coldest winters were also our two longest, the last below zero days ending four day cold snaps on March 1, 1934 and February 27, 1963.
The coldest frigid spell, however, was just seventeen years ago last month, January 15-23, 1994 when the mercury plummeted to double digits below zero seven nights over an eight day period. Several local weather stations reported a record-breaking 27 below zero on the coldest of the cold nights. Many will recall that rolling blackouts became necessary as the cold weather overextended the electrical generation capacity in the Northeast.
Like this year, there was a similarly long spell of cold days as well in ‘94, only two days struggling past 40 degrees from mid-December to mid February. One of the two coldest 24 hour periods ever was during that same spell, when the daytime high recovered to only three below on January 20, 1994. Nine years before in January 21, 1985, we recorded a high of four below after a bone-chilling minus 18 the night before.
Ironically, the mid-eighties marked the beginning of one of the two warm stretches of winters in the century. A string of mild winters that extended through the nineties was interrupted only by the bizarre and record-breaking week in 1994. The other warm spell was a thirteen year span from 1944 to 1956.
Since we are comparing below zero temperatures rather than winter averages, our analysis is not perfect, but the trends shown by these temperature extremes certainly are good indicators of the roughest spells of cold we have had.