Biggest Snowfalls In Above-Freezing Temperatures
In high school science class we learned that snow falls in temperatures of 32° or colder; however, that's not always the case as accumulating snow has been known to fall in air temperatures above the freezing mark - as was experienced three times during the winter of 2018 when 4.4" fell on 2/17, 3.2" on 3/7 and 5.5" on 4/2 (and 5" on 3/3-4 in 2019). This phenomenon happens when snowflakes fall through a shallow layer of air close to the surface that's a few degrees above freezing. If the air is relatively dry, some of the flakes will evaporate, cooling the air enough to keep the flakes from changing to rain. (This is a simplified explanation; a more in-depth discussion on the topic can be found here.)
During the past 100 years four days have had snowfalls of four inches+ on days with temperatures above freezing, six have had three inches or more and 17 days have had accumulations of two inches or more. The 5.5" snowfall on April 2, 2018 has the distinction of being the greatest amount to fall with temperatures above 32°, breaking the previous record set 60 years earlier (4.7" on March 22, 1958). Perhaps the reason so much accumulated was due to the fact that it fell heavily in a short period of time (five hours), thus hindering the rate of melting. And as mentioned in the opening paragraph, the winter of 2019 saw a five-inch snowfall on March 3-4 in which the temperature got no lower than 33°.
Please note that this analysis is limited to days that had temperatures above freezing for the entire day. Days in which snow fell when temperatures were above freezing but also had temperatures of 32° or colder for part of the day aren't included since hour-by-hour precipitation is provided for the liquid amount that fell rather than snow. (However, an exception to this limitation is the snowfall on 2/17 of 2018, when the high/low was 40°/28°, since I actively monitored the hourly temperatures and, therefore, was able to verify that no snow fell during the hours in the morning when temperatures were below freezing. Instead, 4.4" accumulated in the evening/night when temperatures were above freezing.)
The coldest temperature for the dates on the above chart were either 33° or 34°. However, there were a few dates with smaller accumulations in which the coldest temperature was 35°: 3/17/1965, when 1.1" was measured; 3/9/1955/0.1"; 2/15/1950/0.4"; 1/9/1932/0.2" and 4/2/1927/0.1".
Excellent! Thank you for studying this. I thought it was unusual that we had those >32 degree snows, but I didn't realize how unusual. Three of the seven greater than 3 inch snowfalls with the temperature above freezing in the last 100 years occurred within a two month period this year. Amazing.
Posted by: Ken K. in NJ | 04/09/2018 at 12:59 PM
There are at least two more days that had less than two inches of snow in which the coldest temperature was warmer than 34°. an inch of snow fell on November 15, 1906. the high/low was 41/35, and 0.5" of snow fell on November 14, 1908. the high/low was 49/36.
Posted by: William | 12/15/2018 at 11:28 AM