You might say that January 2023 had a January thaw that lasted for the entirety of the month, resulting in New York's mildest January on record (0.3 degrees warmer than Jan. 1932). Temperatures were 9.8 degrees above average, with every day being milder than average. It joined December 2015 as the only two months to have this distinction. Average high/low was 49°/38°. (The high was comparable to Nashville's average high in January, the average low was comparable to Atlanta's.)
On average, January is 5.4 degrees colder than December, but about once every five years it's warmer than December - 2023 was one of these years as January was five degrees milder than December. Only three other Januarys have been more than five degrees milder than the preceding December: Jan. 1990 was 15.5 degrees milder than Dec. 1989 (41.4° vs. 25.9°); Jan. 1911 was 6.3 degrees warmer (36.3° vs. 30.0°); and Jan. 2006 was 5.3 degrees milder (40.9° vs. 35.6°).
After December ended with three days in a row that were ten or more degrees above average, the streak continued for the first six days of January (the January portion of the streak was 17 degrees above average). It wasn't until 1/14 that a reading of 32° or colder occurred; only Jan. 2005 had a later date for this first cold reading (occurring one day later).
The month had 14 days with highs of 50° or warmer; and 15 days were ten or more degrees above average. The mildest reading was 66° (the only day in the 60s). And only three days had highs chillier than 40°, with the coldest high being 38°. Just four days had lows of 32° or colder (21 days is the January average). The coldest reading was 28°, which is the mildest reading to be the coldest for any January. (The previous record was 25° in 1937.)
The most above average day was 1/4, twenty-three degrees above average (high/low of 66°/49°), and since there were no days below average, the least above average day was on 1/14, with a high/low of 38°/31°, two degrees above average.
Jan. 31 was the 35th consecutive day with an above average mean temperature, breaking the previous record of 34 days during the winter of 2015-16 (Dec. 1-Jan. 3).
Besides the consistent above average readings, January had no measurable snow (average amount is about nine inches); but there were traces reported on three days. It tied 2008 and 1933 for being the second least snowy January (Jan. 1890 reported no snow, not even a trace).
With no measurable snow falling in either November or December, Central Park on 1/29 broke the 1973 record for the latest date in a winter without seeing any measurable snow (the first snow finally arrived in the pre-dawn hours of 2/1 when 0.4" accumulated).
Finally, the month's total precipitation of 4.38" was very similar to January 2022's 4.29", about three-quarters of an inch above average. (However, last January's precipitation included 15.3" of snow.) Much of the rain, 3.13", fell in the eight-day period from the 19th to the 26th; the biggest rainstorm produced 1.34" on 1/25-26.
One observation about the five mildest Januarys is that if Jan. 1932 didn't have a high/low of 33°/24° on the last day of the month it would likely still be the mildest January as the first 30 days of the month had an average temperature of 43.7°, 0.2 degrees milder than Jan. 2023. (January 2023 missed meeting the same fate as Jan. 1932 by one day as below average temperatures arrived on Feb. 1.)
Here are previous January recaps (no recap was published for Jan. 2016).