October 2021 Weather Recap: 6th Mildest October Ends With Soaking Rains
After unprecedented rainfall in July, August, and September (each month had more than ten inches), it appeared a respite was in store during October, as the first half of the month was the driest since Oct. 2000, with just 0.15" of rain measured. However, these dry conditions came to an abrupt end in the last week of the month, as 4.71" was measured - the wettest last week of October on record (and eight of the last nine days had measurable rainfall). Much of the week's rain was produced by a nor'easter on the 25th-26th that dumped 3.69" of rain.
The month's other storyline was its mild nighttime temperatures. There was a record streak of lows in the 60s (13 days), which was also the month's total number of days with lows in the 60s, tying Oct. 1879 for the most on record (the average number of lows of 60+ in October is 4). Lows during the first 12 days of the streak were in the narrow 60°-62° range; Day 13's low was 63°. Of the eight longest streaks of lows in the 60s/70s in October, this year's record streak was the coolest.
Overall, the month was 4.1 degrees above average, and became the sixth mildest October on record (it ranked fourth for average low, and tied for 19th for average high). 17 days were five degrees or more above average; seven days had below average mean temperatures. The most above average day was 10/15, which was thirteen degrees warmer than average (high/low of 79°/63°); the most below average day was 10/1 , which was five degrees below average (67°/51°).
Temperatures during October ranged from 47° (on 10/19, 10/24, and 10/29) to 79° (on 10/15). Only three other Octobers have had a smaller temperature range: 1977 (30 degrees); 2004 (31 degrees); and 1894 (31). This mirrored September, which had a 31-degree variation, and was tied for third smallest variation.
In an oddity, there were six days with temperatures stuck in the 60s - the most on record for any month. They occurred in three pairs, and were concentrated in the nine-day period between Oct. 3-11. This narrow temperature range was largely due to persistent overcast skies.
The season's first low chillier than 50° was reported on 10/18, which was the second latest day for this occurrence (latest is 10/20). Additionally, the month's chilliest reading of 47° (reported on three days), was the mildest chilliest reading on record for October (on average, the coldest reading in October is in the upper thirties).
Here are previous recaps of October's weather:
Although October had half as much rain as July, August, and September, the sky index reported much cloudier conditions than the summer months. October’s cloud cover was at 5.4 (on a scale of 10); a normal month’s cloud cover averages a scale of 3.5-4.5. The summer months at least had sunny skies outside of the heavy rainstorms, but in early October a bank of low clouds, some below 2,000 feet, moved in from the ocean. The layer of clouds was responsible for the warm nighttime lows in the low 60s (cloudy autumn nights prevent warm air from being released into the atmosphere as opposed to clear nights allowing Arctic air in). Because of the clouds and varying humidity, this October did not feel too warm or sticky to me, and only three of the warmest days (3, 14, 15) felt summer like. October 2018’s warm stretch under partly sunny skies was much more oppressive with a couple of severe thunderstorms to boot. Finally, we have had two Octobers in a row that failed to reach 80 degrees, after October 2019 had a day with 93 degrees.
Posted by: Henry | 11/02/2021 at 12:46 PM
are you sure this was the sixth warmest October? I thought 2017 was the warmest, 1947 and 2007 were tied for the second warmest, 1949 was the third warmest, 1971 was the fourth warmest, 2021 was the fifth warmest and 1990 was the sixth warmest.
the Octobers of 2017 and 2021 were very similar. both years rank as one of the warmest Octobers. both Octobers were bone dry in the first three weeks and had a three inch rain storm somewhere in the fourth week.
Posted by: William | 11/02/2021 at 05:03 PM
this was the third October in a row with at least five inches of rain. when was the last time there was an October streak this long of this kind?
Posted by: William | 11/02/2021 at 05:10 PM
Since there were five years with a warmer average temperature than Oct. 2021, it ranked sixth. Going to two decimal places, you’ll find the tie between 1947 and 2007 is broken, as Oct. 1947’s average temperature was 63.63 degrees, while Oct. 2007’s was 63.61 degrees. However, even if these two years had the exact same temperature, the two years are counted as separate positions when ranking the years behind it. The way the ranking charts are shown on the NWS site is not how I was taught to do ranks.
Posted by: Rob | 11/02/2021 at 07:47 PM
This current 3-year streak is the longest one in October. This surprised me because five inches isn't a particularly high amount.
Posted by: Rob | 11/08/2021 at 02:06 PM
March had a warmer reading than October this year (82° vs 79°). this also happened last year when March’s warmest reading was 77° and October’s warmest reading was 74°. since 1900, this was only the second time this happened in consecutive years. the first time was in 1989 (82° in Mar vs 77° in Oct) and 1990 (85 in Mar vs 84° in Oct).
Posted by: William | 12/06/2021 at 09:54 AM
This was the 12th October in a row to be above average. However, 2022 will likely become the first October in 13 years to have a below average mean temeprature.
Posted by: Guttmana9 | 10/11/2022 at 08:10 PM