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First look: Friday, Dec. 17 travel
We're keeping an eye on potential disruptions for Pacific Northwest, Texas and Mid Atlantic airports
Welcome to any new readers — we're grateful that you're here! We're building deep learning algorithms to democratize flight delay predictions; until we launch, we're eager to synthesize things manually in our outlooks. These feature several recurring themes that we recognize may be unfamiliar or intimidating, so we’ve written explainers that tackle airport arrival rates, queuing delays in the airspace and different tools to distribute those delays. If there’s a topic or mechanism you’d like to see unpacked, please let us know (same goes for special travel occasions).
We’re kicking off our year-end holiday coverage focused on Friday, December 17th. Forecasting passenger volumes would yield some pretty low confidence predictions given broad impact to travel behavior from COVID, more recent influences from Omicron and this year’s day of week pattern (last time Christmas/New Year’s Day fell on a Saturday was 2010). As a result, we’re going to use domestic capacity to guide our coverage and by this measure, Friday ranks 3rd for the holiday period with 2.60 million seats. Thursday, December 23 ranks first at 2.61 million domestic seats and Monday, January 3 nudges out this Friday by about 1,000 seats for the second spot. Reassuringly, the TSA (who presumably has access to booking data) shared on Monday that Dec. 23 and Jan. 3 are expected to be the busiest days at their checkpoints. Moreover, United shared on Tuesday that they expect travel for the year-end holidays to be busier than Thanksgiving by about 5%.
All that said, what’s on deck for travelers this Friday?
Large scale weather pattern
Strong low pressurewill be lifting north through eastern Canada and, impressively, its trailing frontal boundary looks to stretch from the Canadian Maritimes to Desert Southwest. Along this slow-moving front, showers are expected in the Ohio Valley and thunderstorms for the Southern Plains. Moisture is more limited to the north and east of the Ohio Valley. Meanwhile, the next Pacific system is on track to bring another round of moisture to the Pacific Northwest sometime Friday.
Airport capacity and demand
Given that such a broad swath of the country could see impacts on Friday, we’ll attempt to spend no more than a couple sentences on each airport today then hopefully return with a narrowed focus tomorrow. Before we dive in, we’ll qualify that our efforts are aimed at diagnosing air traffic delays — though not the focus of our efforts (yet), delays owing to aircraft servicing, airline staffing, network effects, etc. are always lurking.
We’ll sort things out alphabetically (by airport code), which means we start with Atlanta (ATL). There’s a low chance (approximately 15%) for the arrival rate to fall to 80, which would create a minor overage (82 scheduled arrivals) in the 8 p.m. hour. Should the 80 rate be realized for the 8 p.m. hour, air traffic delays would likely be manageable with metering and therefore largely imperceptible.
We wouldn't bet against a Runway 19 operation at Washington Reagan (DCA) for at least part of the day — there’s some disagreement on wind forecasts, but a 1 in 3 chance seems about right. DCA can accept about 4 fewer arrivals per hour when landing Runway 19 (as opposed to Runway 1): given some marginal ceilings, that’s the difference between a 34 and 30 arrival rate. That difference would matter in the 4 p.m. and 9 p.m. hours, when 31 and 32 arrivals are scheduled, respectively. Thankfully, an overage of 1 or 2 aircraft is hardly catastrophic and any air traffic delays should be minor.
We’ll be revisiting Dallas-Fort Worth (DFW) tomorrow. We think there’s a 1 in 3 chance that the arrival rate falls to 84 or lower (and a 7% probability for an arrival rate of 72 or lower). Arrival demand peaks at 97 in the 9 a.m. hour; there’s also 91 scheduled arrivals in the 7 p.m. hour. If low-end arrival rates are realized, metering will not resolve the demand/capacity imbalance in either hour and a more-disruptive ground stop seems probable.
While dry conditions should prevail for the New York City area, Newark (EWR) nonetheless warrants mention. EWR’s optimal arrival rate is 48, however it’s only delivered approximately 9% of the time (God bless Runway 11/29). We’d lobby EWR’s “unconstrained” capacity is more realistically a 40 arrival rate (which is also a safe bet for Friday). Unfortunately, flight schedules are built assuming an arrival rate of 48 and demand equals 48 and 43 in the 7 p.m. and 3 p.m. hours, respectively. EWR will be another airport we revisit tomorrow, though we’ll note that the west winds forecast for Friday are at least conducive to using Runway 29 for overflow [and unlocking the 48 rate].
Washington Dulles (IAD) is another somewhat complicated case. We’d put the arrival rate floor between 64-68 (15% chance). Things get a bit murkier on the demand side: scheduled arrival demand peaks at 64 in the 9 a.m. hour, however not all demand is scheduled (and therefore visible). Private jets and cargo airlines are not included in scheduled demand, though they made up 17% of total demand at IAD in the last month. We won’t have an accurate demand picture until flight plans are filed for private and cargo flights (generally day-of), though unforeseen demand introduces some risk that potential delays are understated.
Morning ceilings at Houston (IAH) could very conceivably (i.e. 2 in 5 chance) reduce the arrival rate to 80 — this would be notable, though not overly problematic, during the 8 a.m. hour (81 scheduled arrivals). More worrisome would be a 52 arrival rate (around 1 in 5 chance), which would likely result in a ground stop.
Dry lower levels to start the day at Philadelphia (PHL) should allow the airport to comfortably accommodate their peak demand period (48 scheduled arrivals in the 8 a.m hour). Clouds will be on the increase through the day, however, and precipitation probabilities increase sharply headed into Friday night. We’re a bit more concerned about the 6 p.m. hour, when 45 arrivals are scheduled, and airport capacity is more likely to be constrained. We estimate there’s at least a 1 in 5 chance that the arrival rate ends up below 44. PHL is another one we’ll be keeping an eye on.
We’ll wrap things up in Seattle (SEA), where we think a 42 arrival rate is a reasonable worst case scenario (only 6% chance for lower rate to be delivered). Demand would exceed a 42 rate in the 10 a.m. (44 scheduled arrivals), 6 p.m. (46) and 8 p.m. (44) hours. We’d bet metering could handle these overages (i.e. delays would be minor and largely imperceptible), though the 6 p.m. hour would be borderline.
In all cases that we’re worried about possible disruption, there’s enough uncertainty to refrain from suggesting anybody rebook — let’s wait and see. We’ll be back tomorrow to take a closer look at DFW, EWR, IAH, PHL and SEA, to include some more quantitative predictions.
The National Weather Service has a great online weather school called Jetstream and we’ve linked to its synoptic meteorology topic. In a sentence, high pressure generally promotes fair weather while clouds and precipitation are associated with low pressure.
Unscheduled demand made up 9% of total demand for core 30 airports during the last month, with PHL (15%) and SLC (13%) among other airports that are above average by this measure.