Although 2017 featured two months, February and October, that were the warmest on record, the year may be best remembered for December's Arctic outbreak that moved in on Christmas Day and stayed locked in place through the first week of 2018. On Dec. 28 the high/low of 18/11 made it the coldest day of the year (based on mean temperature), followed on Dec. 31 by the coldest temperature of the year, when the mercury fell to 9° shortly before the ball-drop in Times Square. The last five days of the month had highs of 25° or colder, the first streak of this length since January 2004. Here are some other observations:
- The first six days of December were six degrees above average while the final six days were 15 degrees below average. Overall the month was 2.5 degrees colder than average and was the coldest December in seven years (and the third coldest in 20 years). Until the Arctic front moved through on Christmas Day the month had close to average temperatures.
- For the first time since 2002 December was the coldest month of the year, just the 15th time since 1900 that this has happened.
- The month had 2.21" of precipitation, joining three other months in 2017 with less than 2.50" of precipitation. This was the driest December since 2006 (when 2.15" was measured). The biggest rainfall, 0.75", was on Dec. 5, pouring down that night. This was also the mildest day of the month, with a high/low of 61/50.
- Measurable snow fell on four days, totaling 7.7". The first snowfall, on Dec. 9, was the biggest, with 4.6" measured.
- In addition to the Arctic outbreak at the end of the month, there was a cold snap mid-month that had three days in a row with highs of 32° or colder (Dec. 13-15). During this outbreak there were two 1.2" snowfalls on consecutive days (Dec. 14 and 15).
- The month's nine days with highs of 32° or colder was the most in December since 2000 (which, like this December, ended with an extended Arctic outbreak, the second longest on record, that lasted 13 days, from Dec. 22 to Jan. 3).
- The six-day streak with highs of 32° or colder is behind eight streaks in December of seven days or longer.
- Finally, the high of 18° on Dec. 28 was just the fifth time since 1960 that there was a high in the teens in December.
Here are other December recaps: