Construction at Salt Lake Airport may be producing erroneously high temperatures at weather station

Like many places in the Western United States during summer of 2022, Salt Lake City has been tying old records and setting new ones. Earlier this summer, Salt Lake City International Airport recorded a high of 107°F tying the old all-time record. All six of the first six days of September recorded highs at or above 100°, including a high of 105° on the 6th. This series of heat waves have certainly been historic for the Wasatch Front, but unfortunately it appears that recent construction at the airport has led to changes where the weather station is located, causing it to possibly read temperatures that are a little warmer than what might be observed in that part of Salt Lake City with better siting.

Before 2013, the weather station itself, which I will refer to here as KSLC for simplicity, was sited in an open field surrounded by native grasses and maybe some sagebrush. Since then, however, new construction has occurred so that the weather station itself now sits on a big area of gravel with new buildings and more gravel nearby.

These changes are clearly visible on the image above. The top map is satellite imagery from 2010 while the bottom one was taken in 2020. Airports in many places are ideal settings for weather stations used for long-term climate data on top of the increased aviation safety the stations provide. The reason for this is because airports have large expanses of idle land with native ground coverage – the ideal setting for a weather station.

The World Meteorological Organization, which is the UN’s meteorology body, publishes their Guide to Instruments and Methods of Observation – a manual for government agencies and others to use to ensure weather observations are standardized globally. In the manual, the following guidance is given for artificial surfaces:

Neighbouring artificial surfaces may heat the air and should be avoided. The extent of their influence depends on the wind conditions, as wind affects the extent of air exchange. Unnatural or artificial surfaces to take into account are heat sources, (reflective surfaces for example buildings, concrete surfaces, car parks) and water or moisture sources (for example, ponds, lakes, irrigated areas).

– WMO Guide to Instruments and Methods of Observation, page 44

More specific details are then later given, such as that “A source of heat (or expanse of water) is considered to have an impact if it occupies more than 10% of the surface within a circular radius of 100 m surrounding the [station]…” The present location of the weather station certainly does not meet this standard and based on satellite imagery and the WMO material the weather station may be as much as 9°F away from what a nearby well-sited station may observe.

It does not appear that KSLC is recording temperatures as far above nearby areas as the WMO indicates is possible, but there is evidence to suggest that the station could be a few degrees off. The map above shows high temperatures on September 6 (note KSLC shows a high of 106° instead of 105° noted above due to a rounding error) with KSLC three to five degrees above nearby stations. Of particular interest is the high of 102° recorded by a UDOT site where I-80 meets I-215.

Meteorologists from the National Weather Service office in Salt Lake City visited KSLC on September 7 to do some on-site observations and comparisons, culminating in an excellent thread on the subject on Twitter. During their visit they compared a location with natural vegetation a quarter mile away to KSLC at one minute intervals for a twenty minute period and found no significant difference between the two locations.

Construction at the airport certainly isn’t the only change that has influenced temperatures there. The Great Salt Lake has been shrinking for several years and set a new record low surface elevation again this year. Lowered lake levels allow the water to get warmer during the summer and have moved the shoreline several miles further away from the airport causing the lake to have less of a moderating influence on the weather there. Furthermore, long-term warming of the climate is being observed throughout the region. The National Weather Service addressed these issues in a tweet from September 1:

We’ve had a lot of questions about our Salt Lake City Airport climate site.

Here are some common questions and the related answers. #utwx pic.twitter.com/duTJlOvz18

— NWS Salt Lake City (@NWSSaltLakeCity) September 1, 2022

Thus a brief overview of the situation suggests that if KSLC is recording warmer temperatures because of development in recent years at the airport, it is only by a few degrees Fahrenheit. Still, this difference averaged out over time can be problematic. In a time of changing climate, including large changes in the Salt Lake area (such as the shrinking Great Salt Lake) these data are used by policymakers to determine how to respond and adapt.

I have no information regarding how the decision was made to turn the field KSLC sat on from natural grass to gravel, but it is clear that ensuring the quality of data being observed there was not something that mattered in the end. I don’t know whether that decision was made by the airport itself, the Federal Aviation Administration, National Weather Service, some other entity, or some combination of them.

In any case, because the observing equipment for KSLC is located on gravel, it will frequently be called into question by people without preexisting knowledge of the situation. This certainly includes scrutiny from the general public, but also state and federal agencies, people such as members of Congress and governors, and others. It also decreases public trust in the agencies that oversee our weather observation equipment while the climate is a major consideration for the public and lawmakers by calling into question how other stations are handled.

While the station and surrounding ground remains in this state the local National Weather Service office will have to repeatedly answer questions about the situation. Of course, remedying the situation is not as easy as sending a few meteorologists out there to move equipment around or plant a bunch of native grass. It costs money to maintain (and move) weather station equipment as well as approvals from numerous entities. Steps should be taken to bring KSLC, and other stations, into compliance with WMO guidelines in order to produce the most accurate surface weather data possible.