Weather Blog

Do some Sea-Tac Airport observations need an asterisk?

Do some Sea-Tac Airport observations need an asterisk?
This image from AIR 4 shows Sea-Tac Airport on Wednesday morning, October 30, 2008.

The past few summers have had their heat stretches, but could Sea-Tac Airport's new third runway be making us think we're a little warmer than we actually are?

As many of you know, the official temperature observations for Seattle are taken at the airport. But UW Research Meteorologist Mark Albright has noticed over the past couple of summers that on warm days when the wind typically blows out of the north at the airport, that the official temperature reading there seems to be a few degrees warmer than surrounding reports.

For example, at 1 p.m. on Sunday, the airport reported a temperature of 95 degrees, while some community and private neighborhood weather stations in southwestern King County were reporting temperatures ranging from 88-91. Now granted, those are not official observation stations, but there were a handful that seemed to validate each other.

Another example, taken at 4 p.m. Saturday again shows Sea-Tac the temperature champion of the immediate region as far as local temperature goes. (Temperatures are in red. "KSEA" (lower center) is the airport).:

The anomaly only seems to pop up when the wind is out of the north at the airport, and it seems to be a recent development. So what could be the cause? Perhaps a recent development.

This map shows where the weather observation station is at the airport.

View KSEA Metar Location in a larger map

Note the brand new runway off to the west and northwest? Albright says over the past few years, Port of Seattle officials razed a bunch of trees along the western boundary of the airport, and inserted a massive amount of land fill to build the airport's third runway.

Concrete is a much better heat absorber than vegetation, so it's possible now that north winds are blowing in hotter air than used to be there.

Now, is that really skewing weather data? Hard to say. If you look at surrounding official readings during the last few heat waves, it's not like Seattle is running way ahead. In fact, on the day it hit 103 last July, Sea-Tac was one of the lower readings in Seattle (Boeing Field and Sand Point both reached 105.)

But on the other hand, on Saturday Seattle and Olympia both matched up at a 95 degree high, and on Sunday, Olympia just edged Seattle 97-96. In years' past, Olympia typically has been 2-4 degrees hotter than Seattle on typical hot days.