Was this November Unusually Windy?

 By Meteorologist Intern Richard Castro and Hydrometeorological Technician Amy Seeley

One of the most common questions we were asked by residents of the region over the past week or so is ‘has it been an unusually windy November this year?’ So we took a look at historical wind data going back to November 1981 at Chicago-O’Hare and Rockford Airport, the official climate sites for Chicago and Rockford, respectively. An important qualifier must be noted before we dig into the data we found. November, as stands to reason given the fast movement of weather systems across the country during the cool season, is one of the windiest months on average for the region. Roughly speaking, the windiest months for northern Illinois and northwest Indiana are January, March, April and November. Taking the average wind speeds for all the Novembers from 1981 through 2011 at Chicago-O’Hare and Rockford Airport, we found that the average wind speed for the entire month came in at 10.7 mph for O’Hare and 10.2 mph for Rockford. So, as a starting point, we know that November is already a windy month.

The average wind speed for November 2011 was 11.8 mph at O’Hare and 10.6 mph at Rockford, so these values come in slightly above the 1981-2011 average, more so at O’Hare. But how do these values stack up as compared to the other Novembers since 1981? The table below will rank the Novembers at both locations from 1981-2011 in descending order through the #10 most windy November.

Table 1: November Average Wind Speed Rankings 1981-2011, #1 Through #10
Chicago-O’Hare
 
Rockford Airport
 
Average Wind Speed (mph)
Year
Average Wind Speed (mph)
Year
14.0
1994
12.7
1988
12.9
1989
11.9
1983
12.7
1990
11.8
1987
12.5
1983
11.7
1991&2005
12.0
1992&1993
11.2
1985&1990
11.8
2011
11.0
1984
11.6
2005
10.9
1998
11.5
1987
10.8
1995
11.4
1988
10.6
1982,1989,2011
11.2
1998
10.5
1986
11.0
1984
10.3
1992 & 2003
 
In this context, we can see that this November was fairly windy, and slightly above our 1981-2011 average, but not to the extreme. However, there might be a bit of recent perception involved in how windy it seemed in November. In the Chicago area, November 2005 was almost as windy on average as this past November, but prior to 2005, the last November with an average wind speed of at least 11 mph was November 1998, with 11.2 mph on average. Then, we have to go another 4 Novembers back to find a month with average wind speeds at least 11 mph and this was November 1994, which averaged a whopping 14 mph. So one would be accurate in saying that November 2011 was the windiest November in Chicago since November 1994. This may help explain why to Chicagoland residents, it seemed like such a windy November. At Rockford, this November was the windiest since 2005, so that may provide some helpful context as well.
Are there any other ways we can frame the wind data that may also explain why this November seemed so windy? Taking a look back at the daily wind data for Novembers from 1981-2011, the number of days with average wind speeds at or greater than 10 mph and 15 mph also provided some interesting results, particularly for Chicago-O’Hare. In this case, the tables below will rank the top 5 Novembers from 1981-2011 for number of days with winds averaging at or above 10 mph and 15 mph, respectively.
 
Table 2: Top 5 Novembers 1981-2011- Days with Wind Averaging >=10 mph
Chicago-O’Hare
 
Rockford Airport
 
# Days with avg. wind speed
>= 10 mph
Year
# of Days with avg. wind speed
>= 10 mph
Year
26
1994
21
1985
22
1990
20
1988 & 1989
21
2011*
19
1987 & 1990
19
1995
18
1986
18
1983 &1988
17
2011*
* also achieved in 4 previous years at both O’Hare and Rockford
Table 3: Top 5 Novembers 1981-2011- Days with Wind Averaging >=15 mph
Chicago-O’Hare
 
Rockford Airport
 
# Days with avg. wind speed
>= 15 mph
Year
# of Days with avg. wind speed
>= 15 mph
Year
11
1983
10
1983
9
1989 & 1990
8
1984 & 1988
8
1994
7
1990,1991,2005
7
1991,1993, 2011
6
1998
6
1998 & 2005
5
1985,1987,2011
 
            From the above data, the winds in November 2011 appear a bit more impressive, with the third greatest number of days with winds at or greater than 10 mph at Chicago-O’Hare and tied for the fifth greatest number of days at Rockford. The story is similar for days with winds averaging 15 mph or higher, as November 2011 is tied for the fourth greatest number of days at Chicago and the fifth greatest number of days at Rockford.
            Is there any additional data we can look at? Well, another good measure for strong wind speeds is sustained winds at or greater than 25 mph and 30 mph, respectively. Winds are considered sustained when the same wind speed occurs for at least 2 minutes. As a final means of comparison for Novembers from 1981-2011, the tables below will include the top 3 rankings for number of days when the sustained wind was at least 25 mph at any time during the day and at least 30 mph at any time during the day.        
Table 4: Top 3 Novembers 1981-2011- Days with Sustained Wind >=25 mph at any time

Chicago-O’Hare
 
Rockford Airport
 
# Days with sustained wind
>= 25 mph at any time
Year
# Days with sustained wind
>= 25 mph at any time
Year
10
1994,2005,2011
9
1998,2005,2011
9
1983
8
2003
8
1989
7
1991,1995,2007,2010

 
Table 5: Top 3 Novembers 1981-2011- Days with Sustained Wind >=30 mph at any time

Chicago-O’Hare
 
Rockford Airport
 
# Days with sustained wind
>= 30 mph at any time
Year
# Days with sustained wind
>= 30 mph at any time
Year
7
2005,2011
7
2005
4
1983,1991,1994
6
1995
3
2003
4
2011

 
            In this way, it appears that there was a bit more than recent perception going on with regard to how windy it felt in November. It seems that we had a greater than usual number of significant wind events. For reference, a Wind Advisory is issued when sustained winds between 30 and 39 mph or frequent gusts of between 45 and 57 mph are expected. Therefore, November 2011 saw a pretty substantial number of days where wind advisory criteria would technically be hit in terms of sustained winds alone, especially at Chicago-O’Hare.
            So, to conclude, November is typically a windy month across northern Illinois and northwest Indiana, roughly one of the four windiest months of the year. The average wind speed for November 2011 was slightly above the 1981-2011 average at Chicago-O’Hare and Rockford. So the wind speeds were not extremely high looking at averages alone, but we can say it was the windiest November since 1994 in Chicago and since 2005 in Rockford. What was more interesting in November 2011 was the number of windy days, which fell in the top 5 at both locations in the 10 mph or greater and 15 mph or greater rankings. Finally, the most significant aspect of the wind data for the two sites in November 2011 was the number of days with higher end wind events, marked by sustained winds of at least 25 mph at some point during the day.
 
THANKS FOR READING!


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