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Update: Friday, Dec. 17 travel
Late afternoon and evening disruption at EWR likely; also monitoring mid-morning at DFW
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).
By the end of yesterday’s first look, we had narrowed our focus from 8 airports to 5. Nearly 23% of tomorrow’s scheduled seats touch one of the airports we’re still considering — outcomes at these airports will disproportionately influence how travelers fare on Friday. The large scale weather backdrop is intact, with the frontal boundary mentioned in yesterday’s discussion already draped across a broad swath of the country. The cold front is expected to become nearly stationary tonight and spend tomorrow stalled over the Southern Plains and Ohio Valley. The latest weather forecasts afford a bit more granularity, so let’s into dive into Dallas-Fort Worth, Houston Intercontinental, Newark, Philadelphia and Seattle.
The cold front currently sits over Dallas-Fort Worth (DFW) and as it settles tonight, will actually retreat slightly northward. This modest retreat will allow moisture to stream back into North Texas and low-level clouds will blanket the region for much of tomorrow. Ceilings could conceivably lower to under 1,000 feet, which would pressure airport capacity. We think there’s about a 1 in 4 chance that an arrival rate in the range of 78-84 is realized, which is considerably off of DFW’s optimal 114 rate. The 9 a.m. hour is likely of most consequence, when 97 flights are scheduled to arrive. Given a 78 arrival rate, delays would average about 13 minutes for arrivalsin the 9 a.m. hour. However, we’d bet the FAA would manage this overage with a ground stop, which would allocate delay largely to those flights originating within approximately 600 miles of DFW (i.e. “first tier”). The total delay minutes is the same in both scenarios (slightly more than 1,200 minutes), but when spread across just 37 first tier arrivals (rather than all 97), average delay for those captured flights is 33 minutes.
High pressure building over the Great Plains will eventually dislodge the stalled cold front, sending in back through North Texas late Friday evening. Showers and thunderstorms are expected to accompany the frontal passage, though coverage of thunderstorms still looks to be sparse by 10 p.m., when DFW’s last sizable bank will be underway. Minor delays for northbound departures to negotiate departure fix constrains seems the most probable form of disruption during the evening.
The cold front’s slight drift northward will similarly promote a moist onshore flow to start the day at Houston Intercontinental (IAH). Not only are ceilings forecast to lower (perhaps to underneath 500’), but some guidance (National Blended Model) suggests visibilities could also fall to around 2 miles after sunrise (notably, the TAF keeps visibilities at or above 6 miles). The biggest question will be the 8 a.m. hour, when 81 flights are scheduled to arrive. We think an 80 arrival rate is most likely during this time, which would largely accommodate demand, however we should mention the possibility of a 52 rate (we estimate less than 1 in 5 chance). Should the 52 rate be realized, delays for all flights in the 8 a.m. hour would average about 19 minutes. Like DFW however, we’d bet delays would be administered with a first tier ground stop, and average delays for that smaller subset of arrivals would equal 42 minutes.
The cold front should makes its way through the Tri-State area early Friday morning, with west winds becoming gusty behind it. As we highlighted yesterday, Newark (EWR) is something of a unique airport in that its optimal arrival rate (48) is only delivered about 9% of the time. The optimal arrival rate requires a westerly wind that enables Runway 29 to be used in an overflow capacity, but not so strong as to require that Runway 29 be used as the primary arrival runway. We almost find that sweet spot tomorrow, but still can’t talk ourselves into a better than 1 in 10 chance for a 48 rate. We think EWR’s more “normal” 40 arrival rate will be delivered tomorrow, which unfortunately fails to meet demand in the 3 p.m. hour (43 scheduled arrivals) and 7 p.m. hour (48 scheduled arrivals). The overage in the 3 p.m. hour actually knocks onto the 4 p.m. hour, when first tier average delays would peak near 45 minutes; similarly, the 7 p.m. imbalance manifests itself more so in the 8 p.m. hour, when first tier delays would exceed 30 minutes.
We also estimate there’s a 1 in 10 chance that west winds are too strong tomorrow, Runway 29 is used in a primary capacity and a 38 arrival rate is realized. We’re somewhat less confident as to how delays would be distributed in this case because the overage would be more persistent. Earlier this month, the FAA relied on a GDP with a 1200 mile scope in a similar situation: this would be a middle ground between a GDP capturing all arrivals and ground stops aimed at first tier arrivals. Delays would again peak in the 4 p.m. and 7 p.m hours, though would be kept underneath an average of 30 minutes.
Newark (EWR) is something of a unique airport in that its optimal arrival rate (48) is only delivered about 9% of the time.
Thankfully things are looking better down the road at Philadelphia (PHL). Their next frontal passage will come across during the day on Saturday and ahead of that, rain moves into the area late Friday night. PHL really only needs to get through the 6 p.m. hour (45 scheduled arrivals), which it looks to comfortable do - ceilings should not being to lower until after 8 p.m. We expect no air traffic delays at PHL tomorrow.
A weather system moves through on Saturday, with precipitation sliding onshore ahead of it Friday night. As rain spreads inland, ceilings will lower to around 3,000'. Somewhat similar to PHL, Seattle (SEA) really needs to get through the 6 p.m. hour, when 46 flights are scheduled to arrive. Unfortunately we’re not as optimistic that SEA will succeed in doing so and we think there’s a 15% chance that they deliver an arrival rate between 38-42 (though we’re inclined to the upper end of that range). There’s also 44 arrivals scheduled in the 8 p.m. hour as well as some bunching between 9:55 p.m. and 10:15 p.m. (23 scheduled arrivals). We’d bet later overages are managed with metering or perhaps some limited airborne delay (though difficult to track, we’d expect delays to remain underneath 15 minutes). We’re less confident about how the 6 p.m. hour would be handled. We’ve modeled a first tier ground stop with average delays of 20 minutes. We also wouldn’t be surprised to see some same-center metering that sticks the closest-in flights (e.g. originating from Portland, Pasco, Redmond, Spokane) with relatively long delays of 45 minutes or so.
There’s also some low probabilities (i.e. less than 10%) that a wet snow flake mixes in by the time redeyes are departing. Resulting deicing delays would be minor, but worth mentioning. If you’re curious about winter operations, we recently wrote an explainer on the topic, though Friday night operations at SEA will not resemble the knife’s edge depicted in the linked post.
We think it’d be prudent for any readers with a late afternoon or evening layover in EWR underneath 60 minutes to check for alternative routings, particularly if originating in the Mid Atlantic or Northeast. Similarly, if you’re starting your day in the Southern Plains and connecting through DFW in the 9 a.m. hour, we’d suggest at least exploring rebooking options. The good news is airlines have materially improved rebooking flexibility by eliminating changes fees for most tickets (though a fare difference may still apply). We’ve linked to the same-day change policies for United (who operates a EWR hub) and American (DFW).
We’ll be on Twitter tomorrow to provide some color commentary on our predictions. Otherwise, we’ll be back on Tuesday with a first look at travel on the 23rd!
While our modeling is aimed at tackling arrival delays, there's a strong correlation to departure delays (albeit with some lag and/or possible alleviation). Consider a scheduled "turn" at an airport: the inbound flight is scheduled to arrive at 2:19 p.m. and departs at 3:30 p.m. (71 minutes of turnaround time). Let's say the inbound is delayed by 40 minutes and instead arrives at 2:59 p.m. We'll further assume that the airline doesn't need the full 71 scheduled minutes to turn the aircraft and can accomplish the turn in 45 minutes if they hustle - the departure will push back from the gate at 3:44 p.m. (delayed by 14 minutes). In this example, a 40 minute arrival delay in the 2 p.m. hour is partially passed through to a departure in the 3 p.m. hour. Had the turnaround been scheduled at 45 minutes instead (i.e. no turnaround buffer), the lag between arrival and departure delay would still exist, however the delay would be fully passed through.
And of course, delays resulting from aircraft servicing, airline staffing, network effects, etc. are also always lurking (and not included in our modeling).
Cargo airlines as well as private jets are not included in scheduled demand and only become apparent when the file a flight plan (generally day-of). This unforeseen demand introduces the risk that delay are under-forecast. Unscheduled demand added 7.4% to scheduled demand at EWR in the last month. Unscheduled demand added 5% at DFW and IAH and 5.4% at SEA over the same period.