Nationwide, 2021's top weather events included Arctic cold in Texas in mid-February that shut down much of the state's power grid; searing heat at the end of June never before experienced in the Pacific Northwest; and a deadly tornado outbreak that Kentucky bore the brunt of on Dec. 10-11. Meanwhile, New York's biggest story was the consecutive months of unprecedented rainfall in July-August-September, which culminated in flooding downpours from the remnants of hurricane Ida on the night of Sept. 1, a deluge that was responsible for the deaths of nearly 50 residents of NYC and outlying suburbs (comparable to superstorm Sandy's death toll in Oct. 2012).
The year was the eighth mildest and tenth wettest on record. Eight of 2021's months were warmer than average, led by December (+4.7°, third mildest) and October (+4.1°, sixth mildest). These months book-ended the most below average month of the year, November (-1.8°).
Although the year's nearly 60 inches of precipitation was 10 inches above average, seven of the months had below average rainfall. More than half of the year's precipitation (52%) was in July, August, and September. And nearly half of the rain in those three months came from tropical systems Henri (8.19") and Ida (7.13"). Here are other highlights of 2021:
- A snowstorm that began Jan. 31 and continued into Feb. 2 dumped 17.4”. Most of the accumulation, 16.8", fell in less than 24 hours (Sunday night, Jan. 31 thru late afternoon on Monday, Feb. 1). After this snow event, an additional 10" of snow fell during the rest of the month, bring February's total to 26.0", making it the 8th snowiest February on record.
- March had its first temperature in the 80s since 1998, occurring on 3/26 (82°).
- In addition to the excessively wet months of July-Aug-Sept, there were also periods of very low humidity during the year. For example, nearly half of the days in March had low humidity (below 25%); extremely low humidity was reported on April 6 (7%); and December had it lowest humidity on record on 12/17 (14%).
- The coolest Memorial Day weekend on record (average high/low of 57°/48°) was followed by the ninth warmest June. A high of 98° on 6/30 was NYC’s hottest reading in nine years years, and the hottest reading in June since another reading of 98° in June 1994. But just three days later, July had its first reading in the 50s since 2009, and its coolest high temperature (66°) since 2005.
- July, August, and September each had more than 10 inches of rain (July's amount was above 11") – not only the first time in nine years any month had that much rain, but the first time ever that three consecutive months had this much. This was also the first year to have two rainstorms that produced seven inches+. They were associated with downgraded hurricanes Henri and Ida , and they were less than two weeks apart (Aug. 21-23 and Sept. 1).
- On the night of 9/1, Ida's rain poured down in just five hours time (and 3.13" in one hour). More rain fell between 9-10 PM than fell in all of November and December.
As an aside, this one-hour amount was trumpeted by the National Weather Service as being Central Park's greatest one-hour amount on record - but this claim was in error, as NWS's own records show a greater 60-minute amount on Sept. 5, 1913, when 3.31" of rain was measured between midnight and 1 AM - 0.18" more than Ida's 60-minute gully washer. (11 days earlier, a one-hour amount of 1.94" during Henri also had the NWS claiming it was an all-time record, which was even more in error, as there have been at least a dozen instances of greater amounts in an hour, most recently in July 2018.)
- October had a record streak of lows in the 60s - thirteen days in a row. It also set a record (for any month) of days with high/lows stuck in the 60s. There were six such days, concentrated in the nine-day period between Oct. 3-11. Finally, October's coolest reading of 47° was the mildest reading to have this distinction.
- The final week of October was the rainiest on record (4.71" fell). That week accounted for more than half of the precipitation measured from October thru December. This rainy week was followed by the driest November-December on record. These two dry months prevented the year from reaching the sixty-inch mark in precipitation, coming in at 59.73". After 31.44" fell in July-September (32.09", if rain on 6/30 is included), 12 of the 13 weeks in October-December had less than 1/10 of that amount (3.06").
Here are recaps of previous years: