Figure 1. The five most difficult daily low temperature records to break in Fairbanks using 1981-2010 normals.
In looking at the hourly observations for Fairbanks for the time period of May 6th through May 11th, a sharp cold front clearly passes through Fairbanks around 6 p.m. on May 7th, 1964. The temperature dropped precipitously and the air pressure rose over 20 mb in 12 hours. Figure 2 shows the air and pressure readings during this time period. On 5 of the 6 days, the official low temperature deviated from the hourly observations by no more than 1°F. However, on May 9th, the lowest hourly temperature reading was 5°F at both the 5 a.m. and 6 a.m. observations. Readings of 6°F were measured at 2 a.m., 3 a.m., 4 a.m., and 7 a.m. To achieve a low temperature of -1°F, the temperature must have dropped and rebounded by at least 6°F between hourly observations. This situation occurs occasionally during the dark winter months but a mechanism to explain this phenomenon in the month of May in lacking. Not shown on the chart is a consistent wind from the north between 7 and 12 mph during the time period with temperatures between 5°F and 6°F.
Figure 2. Hourly air temperature and pressure measured at the Fairbanks International Airport between May 6th and May 11th, 1964.
Looking at the temperatures regionally, I pulled all the station data for Alaska during the May 8th to 10th, 1964, time period to find the lowest temperature. A three-day period is used to negate the effect of observation time effects shifting an observation to the following day. Figure 3 shows the lowest temperature during this time period.
Other that the Fairbanks International Airport reading of -1°F, no other station around town was colder than +2°F. The only other station with hourly observations was Eielson Field. Their low temperature on May 9, 1964 was 4°F and their lowest hourly observation was also 4°F. Given the correlation between the hourly readings and the official daily minimum on all days except May 9th at Fairbanks International Airport, it seems unlikely that any sort of sloshing of airmass occurred which could account for intra-hourly reading anomalies.
It is worth emphasizing how uncommonly cold this airmass was for May. The values shown in Figure 3 would be uncommon for early April, much less early May. The 850 mb temperature at Fairbanks was -25.6°C on 5/9/64 at 12Z. No other May has seen an 850 mb temp below -20°C.
So, is the -1°F a valid reading? In my opinion, it is a questionable reading that requires further investigation.
Brian, Interesting analysis. Another factor is that there was no snow cover left, which makes it less likely that a brief pause in the wind allowed for a sudden drop in temperature.
ReplyDeleteI can see a situation whereby cold air drained down the Chena River from the NE (where it was colder as noted ) and flowed through town. The river adjoins the airport along its north and west perimeter.
ReplyDeleteThe other nearby observation stations were either away from the river and somewhat higher, or to the SE away from the river's influence.
No way to prove that conjecture, but dwellers along the Chena and its tributaries upstream from Fairbanks can often report colder temps than in town.
Gary
Nice analysis Brian. I'll look into this. It is possible that the daily temperature extremes for this time period were being made at a different location than the hourly temps, as the first electronic type temperature sensor was installed at Fairbanks International in August 1963. So perhaps the daily extremes were still being taken from liquid-in-glass thermometers.
ReplyDeleteGood information regarding the equipment history. Let me know what you find out. If the daily min/max was obtained from the same thermometer that the hourly observations were taken from, there doesn't seem to be a way that the -1°F could be valid.
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