There are two climate sites at the Fairbanks International Airport. The main station is called Fairbanks International Airport. That is the official climate site. The secondary site is called Fairbanks Airport #2 and is closer the the terminal. When looking at the May data a few days ago, I noticed that the secondary site was actually below normal for the month wile every other station in the region was above normal (See Figure 1). As it turns out, the average daily temperature at the #2 site was 3°F less than at the primary station. Figure 2 shows the locations of the two stations as shown in the NCDC records and the May 2014 monthly temperature and departure from normal.
Figure 1. May 2014 daily average temperature at Fairbanks International Airport and Fairbanks Airport #2.
Figure 2. Station location for Fairbanks International Airport and Fairbanks Airport #2 along with the monthly average temperature and departure from the 1981-2010 normal. Note: the Airport #2 site uses an 11-year period of record for their normal calculation.
This begs the question of whether one station is reporting inaccurate temperatures. Since the primary site's temperature departure is consistent with the other regional stations, I am inclined to place much more weight on the primary station than the #2 station. Figure 3 shows the statewide departure from normal for the month of May 2014. With the exception of the area around Bettles and Nome, all of Alaska was above normal for May.
Figure 3. Statewide temperature departure from 1981-2010 normal.
Looking back of the Fairbanks Airport #2 period of record and comparing it to the Fairbanks International Airport station during the same time period should provide a good assessment of whether there is a consistent temperature bias. Figure 4 indicates that the Airport #2 site is consistently cooler than the main climate site. The average annual difference is 1.4°F.
Figure 4. Fairbanks International Airport and Fairbanks Airport #2 annual temperatures from 2000 through 2013.
Figure 5. Average monthly temperature difference between Fairbanks International Airport and Fairbanks Airport #2 from 2000 through 2013. Positive numbers indicate that the Fairbanks International Airport site was warmer.
Perhaps more interesting is the strong and consistent seasonal variation. As we can see in Figure 5, there is temperature parity during the months of February, March, and April. However, that transitions into a strong temperature differential for the remainder of the year – peaking in the high sun months.
So why is there a difference and does it matter? The answer to the first question is difficult to answer without inspecting the station equipment and its siting.Figure 6 shows the locations of the Fairbanks International Airport station since 1929. Interestingly, the location from 1952 to 1997 is very close to the current Fairbanks Airport #2 site. It is possible that they might actually be the same location.
In my opinion, the Fairbanks Airport #2 temperature readings are too low. As for the why does it matter question, the short answer is that better data always yields better results.
Figure 6. Station history for Fairbanks International Airport site from 1929 to present. Source: http://www.ncdc.noaa.gov/homr/
For comparison, I added three of the four main stations in Anchorage: Anchorage Forecast Office (PAFC), Anchorage International Airport (PAFC), and Anchorage Merrill Field (PAMR). I excluded Lake Hood (PALH) since it is located right next to a large body of water. The Forecast Office and the International Airport are pretty close to each other and are both quite close to the moderating influence of Knik Arm. Merrill Field is several miles inland and has a slightly more inland climate. That is particularly apparent in the warmer temperatures during the summer months. All-in-all, there is very little annual and monthly variability in the readings between the stations. The Forecast Office and the Airport have highly similar temperatures as one would expect – and as I would expect in Fairbanks. The Merrill Field temperatures are a little bit warmer on an annual basis. I attribute this to it being located in a more urbanized setting.
Figure 7. Anchorage, Alaska, annual temperatures from 2000 to 2013 for the Anchorage Forecast Office (PAFC), Anchorage International Airport (PAFC), and Anchorage Merrill Field (PAMR).
Figure 8. Anchorage, Alaska, monthly temperatures from 2000 to 2013 for the Anchorage Forecast Office (PAFC), Anchorage International Airport (PAFC), and Anchorage Merrill Field (PAMR).