Wind Chill Climatology

We have devoted a lot of time discussing wind chills over the last few months, so what harm is there in another post, right? Yesterday a comment showed up on a post regarding the cold temperatures in the Lower 48 as compared to Alaska this winter. The comment noted that while temperatures are usually colder in Fairbanks, the windier conditions in the northern Great Plains might make them colder as measured by wind chill. Since there are not very many unsolicited analysis requests, I thought it would be interesting to see if the commenter was correct.

I first took a look at the winter (December, January, and February) wind chills in Fairbanks, Fargo, Bismarck, and International Falls, since 1984. The wind chills for each station were generated by calculating a daily wind chill (from the average daily temperature and the average daily wind speed) and then taking those 90 days (or 91 days in a Leap Year) and averaging them together. That seems like an awful lot of averaging. To corroborate, I looked at four years of hourly observations for each station and generated a seasonal average and compared those to the daily average. The numbers were nearly identical. Therefore, my confidence in the daily average value is high. Figure 1 shows the results of the average daily winter wind chill for the four stations listed above. Indeed, Fairbanks has a lower daily windchill than the other three stations nearly every winter. This past winter is the exception to the 30-year period. In no other winter was Fairbanks behind the other three stations.

Figure 1. Time series of wind chills in Fairbanks, Fargo, Bismarck, and International Falls.

Winter 2013-2014 Wind Chill:

When looking at the entire U.S., there is actually quite a large area whose winter-long average wind chill was colder than Fairbanks. Stations in six states had winter wind chills that were lower than Fairbanks. Figure 2 shows the this winter's average daily wind chill for Alaska and Figure 3 shows this winter's average daily wind chill for the Lower 48.

Figure 2. Average daily wind chill in Alaska during the winter months (DJF) in 2013-2014. This map was generated from only those stations that reported daily average wind and daily temperature for a minimum of 85 out of 90 days (41 stations).

Figure 3. Average daily wind chill in the U.S. during the winter months (DJF) in 2013-2014. This map was generated from only those stations that reported daily average wind and daily temperature for a minimum of 85 out of 90 days (889 stations).

Winter Wind Chill Climatology:

Making a 30-year wind chill climatology is a little more challenging. Due to the number of records in the database that would require processing over that time period (~18,000,000) and the limited power of my computer, a shortcut was needed. I was able to use the 30-year climatology of wind that I processed a week or two ago for all primary stations with complete records for 28, 29, or 30 years (which involved several computer crashes). That data set was then combined with the NCDC normals data set and a raster calculation of the two could commence using the 2001 wind chill formula. As a check of the results, I manualy processed several stations using an hourly method, a daily method, and a seasonal method.

For example, the Fargo, ND, 30-year normal DJF temperature is 12.6°F and their 30-year average DJF wind speed is 12.4 mph. That produces an average wind chill of -2°F for the entire three month period over 30 years as a single calculation. If you take each individual daily temperature and wind speed over a 30-year period, the average of those 10,950 daily wind chills for Fargo is -1°F. I also looked at hourly observations for several years and they were within a degree too. So, it is not an exact match but in my opinion it is certainly good enough.

Figures 4 and 5 show the 30-year climatology of winter wind chills for Alaska and the Lower 48 respectively. On average, Fairbanks' wind chill is far lower than anywhere in the Lower 48. Even Anchorage is lower than 90%+ of the Lower 48. So, while the Lower 48 may have bested much of Alaska for wind chill coldness this winter, on average, it is not even close.

Figure 4. Normal daily wind chill in Alaska during the winter months (DJF). This map was generated from those stations that have a 30-year climatology of daily wind speeds (41 stations) and a published NCDC normal daily temperature (189 stations).

Figure 5. Normal daily wind chill in the Lower 48 during the winter months (DJF). This map was generated from those stations that have a 30-year climatology of daily wind speeds (889 stations) and a published NCDC normal daily temperature (7,454 stations).