Seattle-Tacoma International Airport (SEA, KSEA) serves Seattle, USA and has 3 runways. Below you can see the latest wind and weather report, how that wind lines up with every runway end, and what the layout means for how the airport works.
All 3 runways point the same way (north-south), so a strong wind from the side is a crosswind on every one of them. Headings are true (not magnetic), so they differ from the runway number by the local magnetic variation.
| Runway | Length | Width | True headings |
|---|---|---|---|
| 16L / 34R | 3,627 m (11,900 ft) | 46 m | 180° / 000° |
| 16C / 34C | 2,873 m (9,426 ft) | 46 m | 180° / 000° |
| 16R / 34L | 2,591 m (8,501 ft) | 46 m | 180° / 000° |
Aircraft take off and land into the wind whenever they can. A headwind slows the ground speed at touchdown, shortens the runway needed and gives better control. A tailwind does the opposite, so airports normally limit it to a few knots. A crosswind (wind across the runway) is harder on the pilots, and large jets have a limit on how much they can accept.
Each runway has two ends, numbered by compass heading divided by ten, so 27 points west and 09 points east. The same strip of tarmac is used in either direction depending on the wind, and parallel runways add L, C and R (left, centre, right) to tell them apart.
All three of Sea-Tac's runways run north-south and are parallel, so there is no crosswind runway to switch to: a strong wind from the east or west is a crosswind on all of them. South flow, with landings heading north, is the most common arrangement, and northerly flow happens when the wind swings round.
AeroGaze can't see air traffic control's runway plan. It shows the latest wind from the KSEA METAR set against each of the 3 runways: aircraft take off and land into the wind where they can, so the runway ends with the strongest headwind are the likely candidates. Noise rules, traffic and the forecast also play a part, so treat it as a guide, not a fact.
Seattle-Tacoma International Airport has 3 runways: 16L/34R, 16C/34C, 16R/34L. All 3 runways point the same way (north-south), so a strong wind from the side is a crosswind on every one of them.
Runway 16L/34R, at 3,627 m (11,900 ft) long and 46 m wide.
There is no single limit. Each aircraft type has a demonstrated crosswind figure, commonly in the range of 30 to 40 knots for large jets, airlines set their own limits (often lower on wet or contaminated runways), and the pilots decide on the day. When a strong wind blows across the runways at Seattle-Tacoma Airport, you see more go-arounds and diversions.
From the METAR reports that NOAA's Aviation Weather Center publishes for KSEA, refreshed about every ten minutes. A METAR is usually issued once an hour, and sooner if conditions change, so the observation time on the page shows how fresh the report is.
They are flight categories based on cloud height and visibility. VFR: cloud base above 3,000 ft and visibility over 5 miles. MVFR (marginal): 1,000 to 3,000 ft or 3 to 5 miles. IFR: 500 to 1,000 ft or 1 to 3 miles. LIFR: below 500 ft or under 1 mile. The lower the category, the more spacing between aircraft and the more delays.
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Sources: wind and weather from the NOAA Aviation Weather Center (METAR). Runway coordinates from OurAirports (public domain); runway notes are editorial. AeroGaze is an independent site, not affiliated with any airport or air traffic service.