The chart below shows the 1981-2010 daily normal temperatures for the Gulkana airport, which is just a few miles from Glennallen, and for the Fairbanks airport. Fairbanks sees a somewhat larger swing from summer to winter, but overall the large seasonal variations are similar. Peak summer temperatures occur a few weeks later in Gulkana, which reflects a slightly greater maritime influence in the more southerly location.
In high summer (June and July), the differences between the two locations are more significant compared to the range of temperatures observed at that time of year. As shown in the charts below, Gulkana is quite a bit cooler, especially for the daily minimum temperatures. Minimum temperatures are generally in the 40s in Gulkana, but are more often above 50 °F than below 50 °F in Fairbanks. In Gulkana, daily high temperatures most often fall in the range 60-75 °F, but Fairbanks is typically in the range 65-80 °F.
The cooler temperatures overall in Gulkana can be explained partly by the higher elevation (1560' vs 430' MSL). Cooler nights in particular are the result of lower humidity: Gulkana's average dewpoint in June and July is 41 °F, compared to 47 °F in Fairbanks. Accordingly, Gulkana is about 10 percent drier in terms of June-July precipitation. Longer nights may also play a role in nighttime coolness: the sun is below the horizon for at least 4 hours every night in summer in Gulkana.
Lastly, I'll touch on the correlation of temperature variations in the two locations. The list below shows the correlation coefficients between the two locations for daily temperature departures from normal, based on the 1981-2010 normals and calculated over the common period of record (1943-2014). Correlations are highest in winter and spring, and are relatively low in late summer when it appears that local variations in cloudiness have a large effect compared to the underlying temperature variance.
The few times I've been through the area it's been somewhat windy. Is it more windy there? And wouldn't that explain the more moderate temps in winter?ReplyDelete
Eric, yes - it is more windy than Fairbanks. Since 2000, the mean wind speed in Dec-Feb (from all hourly observations) is 3.4 mph in Gulkana and 2.1 mph in Fairbanks. Perhaps more usefully, sustained wind speeds of 10 mph or higher are observed 10.5% of the time in Dec-Feb in Gulkana, but only 3.5% of the time in Fairbanks. This would certainly make a difference for temperatures.Delete
Thank you Richard for fulfilling a promise I made to answer a co-worker's question in 1981. I had flown with him to Tolsona Lake Lodge (Chet and Bessie were owners), and we discussed the temps of that locale (and Gulkana) versus Fairbanks in winter.ReplyDelete
He had lived there in the early '60's and claimed it was (or could be) as cold as Fairbanks. I disagreed, but without reference.
Now I see it's possible and likely a cold spot similar to the McGrath and Northway areas both at lower latitudes than Fairbanks.
Location, elevation, drainage advection and winds, and cloud cover all play a role in determining temperature.