Guide
Seattle and Portland airports: why the evening flight holds up
Flights leaving Portland ran 82.5% on time and Seattle-Tacoma 79.5%, with some of the flattest morning-to-evening curves in the US. Rain is not the problem; summer is.
Swap a 6am departure from Portland for a 6pm one and your odds of arriving on time fall by 10.6 points. Make the same swap across the country as a whole and they fall by 21.3: nationally, departures in the 5am–8am window arrive on time 89.3% of the time and those in the 5pm–8pm window only 68.0%. At Seattle-Tacoma the slide is 13.4 points.
Few big airports in the country hold their schedule through the day this well.
Over September 2025 to August 2026, flights departing Portland International arrived on time 82.5% of the time, and flights departing Seattle-Tacoma International 79.5%. An airport's figure here covers its departures, scored at the destination gate by the DOT's 15-minute rule.
US average 77.3%
65.0%90.0%
Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Two fields, two scales
Seattle-Tacoma is the bigger operation by a wide margin: 164,759 scheduled departures a year against Portland's 63,784. It is Alaska Airlines' main hub and Delta's West Coast gateway to Asia, and it runs a connecting schedule. Portland is mostly origin and destination traffic, a large share of it flown by Alaska and its regional partner SkyWest.
Both do well on the measures that matter when something goes wrong. Only 4.5% of Portland departures landed an hour or more late, and 5.3% of Seattle's, against 8.3% nationally. Cancellations ran 0.74% and 0.93%, about half the national 1.89% or less. Portland ranks 4 of 60 airports for on-time departures. Seattle ranks 21.
Why the day stays flat
Seattle (SEA)79.5% overall
Portland (PDX)82.5% overall
All panels share one scale, 65% to 95% on time. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Evening delays elsewhere are mostly inherited. An aircraft that falls fifteen minutes behind on its first leg rarely wins the time back, and by its fourth or fifth leg the losses add up. The DOT records this as "late-arriving aircraft", which accounts for 40% of delay minutes nationally. At Seattle-Tacoma it is 29%, and at Portland 36%.
Two things are consistent with that. The Pacific Northwest rarely gets the afternoon thunderstorms that wreck evening schedules in Texas, Florida and Colorado, so there is no daily convective hit landing on the late windows. And the dominant carrier is unusually level through the day: Alaska Airlines ran a gap of just 12.1 points between its early-morning and early-evening departures across its whole network, one of the smallest of the 14 reporting airlines, against 20.1 for the median carrier.
The morning is still the best window at both airports: 88.8% at Seattle and 88.1% at Portland. The point is that the penalty for flying later is small, which makes the Northwest one of the few places where the evening flight is a reasonable choice rather than a gamble.
Rain is not the problem; summer is
Seattle's reputation would predict a bad winter.
The data does not show one. Seattle's best month was April at 85.6%, and its worst July at 71.8%. Portland ran best in February (86.3%) and worst in July (78.0%).
Seattle (SEA)79.5% overall
Portland (PDX)82.5% overall
All panels share one scale, 65% to 90% on time. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Steady Pacific rain lowers visibility but rarely stops an airport the way a line of thunderstorms or a snowstorm does, and both fields handle it every week from October to May. Summer is different, for two reasons that fit the numbers. It is the peak season for Northwest leisure travel, including the Alaska cruise departures that fill Seattle's schedule. Northwest flights in July fly into the country's worst month, when July runs 71.7% on time nationally, and the aircraft arriving from storm-hit hubs bring their delays with them.
December is the other soft spot: 74.0% at Seattle and 79.3% at Portland, when holiday volume meets the occasional snow or ice event. The region sees too few of those to handle them as routinely as Denver or Minneapolis, which likely makes each one costlier.
The airlines at Seattle-Tacoma
SEA average 79.5%
60.0%90.0%
Carriers with at least 1,000 scheduled flights at the airport. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Alaska flies the largest share of Seattle departures, so the airport's average leans on it. Across its network Alaska ran 79.7% on time with a cancellation rate of 1.20%. (From January 2026 that network figure includes Hawaiian Airlines' flights, inter-island hops too, which the DOT file reports under Alaska's code from that month.) At Seattle its mainline operation sat a little below the airport average in this data, while SkyWest, which flies regional jets for both Alaska and Delta, ran above it. Delta, the second-largest operator, ran 81.1% across its network. Southwest is a small presence at Seattle and sat near the bottom of the chart, as it did at many Western airports.
The practical upshot: on a Seattle departure, the regional jet is not the weak option it can be elsewhere. The carrier table on each route page shows the split for your specific city pair.
Routes around the Northwest
The short hops that knit the region together run well. Seattle to Portland ran 82.2% on time and Portland to Seattle 84.9%. Seattle to Spokane ran 83.1%.
The smaller regional fields have no page of their own, but their headline figures fit the pattern. Departures from Boise ran 83.4% on time, from Spokane 84.3%, and from Anchorage 85.1%, all above the national 77.3%.
US average 77.3%
50.0%90.0%
Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Anchorage shows how much direction matters, and why the pipeline keeps the two directions of a route as separate records. Anchorage to Seattle ran 86.9%, while Seattle to Anchorage ran 76.5%, and just 54.6% in December. Arrivals are what the DOT measures, and in December the arrival end of that route is a subarctic airport with long nights and snow and ice on the runways.
The weakest routes out of both airports go to San Francisco. Seattle to San Francisco ran 59.8% and Portland to San Francisco 66.8%, and 58% of Seattle-to-San Francisco delay minutes were charged to the National Aviation System, the DOT category for airport capacity, traffic volume and air traffic control programmes. The problem sits at the arrival end: San Francisco's closely spaced parallel runways lose capacity in low cloud, and the delays are handed out as ground holds at the departure airport. On both routes the damage was concentrated in the spring and early summer of 2026: Seattle to San Francisco ran 40.7% on time in May and 35.0% in July, against 76.2% in January. When those spring months first came through, I took them for a bug in my aggregation; checked against the raw month files, they are in the data. The data does not say why. The Bay Area guide covers the alternatives at Oakland and San Jose.
How I would use the Northwest's flat day
Take the flight that fits your day. At Portland and Seattle the evening penalty is a fraction of the national one. The morning is still best, but a 5pm departure here is not the gamble it is in Orlando or Dallas.
For July and August, add slack. Both airports ran their worst month in July in this data. Leave a longer connection downline in summer than you would in February.
Heading to the Bay Area, consider Oakland or San Jose. The Northwest end is rarely the problem on those routes. San Francisco's arrival rate is, and with Seattle to San Francisco at 40.7% in May 2026, I would not route a spring connection through SFO from here.
Flying to Anchorage in winter, go early and expect variance. The northbound run carries far more winter risk than the southbound one, and a morning departure leaves room to rebook if Anchorage is closed.
Connecting at Seattle to Hawaii, check the second leg as closely as the first. Seattle to Honolulu ran 66.2% on time, well below Seattle's average, and a missed connection to a five-hour overwater flight costs hours rather than minutes.
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