February 21, 2024
February 16, 2024
February 8, 2024
Originally published February 2021; updated January 2024.
When the weather outside is frightful … and you’re worried your trip won’t be so delightful, here is everything you need to know about Seattle-Tacoma International Airport’s (SEA) winter weather operations. We don’t want to go so far as to say “Let It Snow.” But if it does, we will be ready.
SEA is one of the top 12 busiest airports in the country and averages 1,200-1,300 flights per day. So, as you know, even a little bit of bad weather can have a big impact on flight operations. The Airport team works all year and around the clock to prepare for, respond to, and communicate with you about inclement weather, whether it’s rain, snow, sleet, smoke, or fog.
In a normal season, SEA Airport budgets about 4,000 hours for snow removal. In the last 10 seasons, the airport has seen an average of six inches of snow. The biggest season in that period was 2018-19 with 21 inches, followed by 2020-21 with 12.9 inches and 2016-17 with 11.2 inches.
Bad weather is rarely a surprise to the airport team. Before you even know it’s coming, the SEA team has been getting ready and planning for the worst. Here’s how.
SEA Airport has access to weather information through NOAA and the National Weather Service 24 hours a day, 7 days a week, 365 days a year. There is a National Weather Service weather sensor right at the airport for accurate readings and the airport contracts with an additional weather provider for custom weather forecast reports.
Before winter weather begins, the airport opens the Snow Control Center, a central management operation for all airport snow and ice control activities. It facilitates communications and speedy decision making in a larger snow and ice event.
The snow team is made up of 99 people — 74 members of the Port and SEA teams who are trained in snow removal, and 25 mechanics standing by to make sure the equipment works. By the time bad weather hits, the snow team has already been preparing. Months before, they begin checking the equipment, stocking up supplies like sand and de-icer fluid in the snow shed, practicing with the equipment, and getting ready for the inevitable.
SEA Airport has more than 50 pieces of equipment on hand for snow and ice maintenance including:
Every November all members of the snow team go through recurrent training. The ops staff review the snow and ice control plan, and re-familiarize themselves with the snow alert levels. The maintenance staff reviews the plans, but they also go out in the snowplows and do mock snow removal exercises on the airfield.
The airport stocks up the snow shed with runway de-icer and sand. The following supplies are on hand and ready for deployment:
When Mother Nature gets cranky, winter weather operations kick into high gear. During a weather event here’s what’s happening behind the scenes.
The fluids used for de-icing airfield pavement are different than the substances used to de-ice airplanes. Chemicals are sprayed on the wings and fuselage of a plane to prevent icing. Each of the airlines are responsible for providing de-icing fluids and applying it to their planes.
On the airfield, SEA Airport handles all common use areas and manages de-icing of the runways, taxiways, ramp areas in and around the gates and cargo area, and adjacent airport roadways. Airlines are responsible for clearing ice and snow from their specific gates.
Snow removal on the runways takes place with several snow plows stretched out at an angle with snow blowers following.
Snow removal happens in the following order:
Priority 1: Runways, taxi lanes, and taxiways
Priority 2: Hardstands (when an airplane is parked and passengers are transported by bus to the airports. SEA uses this operation to get passengers on and off planes more quickly rather than waiting for a gate during busy times).
Priority 3: Bagwell ramps, vehicle service roadways, sloped roads
De-icing occurs before snowfall when temperatures reach 33-34 degrees. De-icing fluid works to stop ice from bonding to the concrete. The runways have embedded temperature monitors that allow staff to apply de-icing fluid only when necessary in order to conserve the supply. The airport uses biodegradable potassium acetate as a liquid runway de-icer. A solid runway deicer, sodium acetate, also is used at lower temperatures. On-site tanks store 62,000 gallons of de-icing fluid and supplies are restocked during the winter to maintain an acceptable stockpile.
In case you’re wondering about the environmental impact, the de-icer solution used on the ground does not harm streams. The airplane de-icing solution is collected through an industrial wastewater system and is sent for secondary treatment at a King County treatment plant.
SEA Airport is responsible for maintaining the terminal and facilities, including:
The Port monitors the roadways and facilities around the airport for snow and ice. This includes airport ground transportation, public parking, and employee parking. And the buses between the terminal and the employee parking lots and rental car facilities.
In case you’re curious, here are a few stats about ground transport operations:
Flights can be delayed in the event of low visibility like snow, fog, and even smoke from forest fires.
Here are a few terms you may hear during weather operations.
A gate hold is when aircraft are required to stay at the gate until air traffic has a spot for them to depart and is managed by the Federal Aviation Administrator or the Port.
A ground stop is a traffic management procedure taken by Air Traffic Control (ATC) during low visibility periods for the safety of aircraft, passengers, and operators. Most often ground stops are used to hold aircraft on the ground at originating airports before they head to their destination.
With reduced visibilities, the arrival rate would be reduced. On a typical sunny day here at SEA, the airport could see 50 aircraft arrivals per hour. On a hazy, foggy, or snowy day, it could decrease to 25 or fewer arrivals per hour in worst cases. Simply put, as it gets harder to see, safety procedures require ATC to build in greater distance of separation between aircraft, thus fewer can land within that hour.
A ground stop allows ATC to ‘meter’ traffic to the destination airport. This process spreads out traffic volume along the flight path to match the arrival rate so when aircraft get to the destination they won’t be delayed further for landing clearance. Often this can be as little as 15-30 minutes to clear volume congestion within the route and the aircraft is released from its origination airport.
Every flight is different depending upon departure time, destination, and international or domestic origin. So don’t assume that all flights are delayed – check with your airline for the most up-to-date information.
There are several tools you can use to find out what is happening during a weather incident and year-round.
SEA Airport Home Page
If there is a weather event or other incident, check the SEA Airport home page for a colored alert bar or an incident advisory graphic.
Flight Aware’s Flight Cancellations Page
The Flight Aware site tracks airport delays and cancellations daily. To track SEA Airport flight status, enter "KSEA" into the "Filter all stats by airport" box.
SEA Flight Information Online
The Flight Status page provides the same information seen on the in-terminal flight information displays, which comes directly from the airlines. You can use this page to check the status of specific flights, or delays to or from another airport. For example, to check delays or cancellations for flights to Chicago, select the Chicago airport under Destination, then leave the Select Airline field blank.
Or contact your airline directly about your flight status.
Weather Conditions at SEA Airport
Get the latest conditions and forecast from NOAA/the National Weather Service.
SEA Airport App
Download the SEA Airport app for your iOS and Android devices to get updates on your flight and security checkpoint wait times.
SEA Airport Social Media
Real-time updates are posted to the SEA Airport Facebook page and X feed.
SEA Airport Text Alerts
Sign up to be notified of a weather incident or receive alerts during peak travel periods.
Sound Transit Alerts
View service alerts or sign up for email and text alerts from Sound Transit.
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