Discover more from Aerology
Outlook: MLK weekend return travel
American suspends CLT operations on Sunday through 3 p.m. (at least); moderate freezing rain in Washington may disallow takeoff
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).
TSA screened 1.73 million passengers yesterday, as travelers headed out for the long weekend (and in line with our predictions, we might add). While outbound travel was relatively smooth, unfortunately return travel looks to be tougher sledding. A storm developing over the Lower Mississippi Valley will move eastward to the Southeast by Sunday morning, where it will produce significant areas of freezing rain for the Mid Atlantic as well as Central and Southern Appalachians. The system will then head northeastward by Monday, spreading heavy snow into the lower Great Lakes and delivering a wintry mix for areas east of I-95. Weather Service Offices have blanketed the East Coast in winter weather alerts accordingly.
Before we dive into airport-specific forecasts, we also want to reiterate our warning from the outbound outlooks: though some States appear to have crested their Omicron case peak, sick calls have recently approached 1/3 of planned staffing levels in some cases1. How does this manifest itself? Perhaps a missing gate agent prevents you from boarding on-time; or maybe the absence of wing walkers will stop you just short of your arrival gate. Unfortunately, winter operations will only exacerbate this perceptible sluggishness, as it requires additional processes be staffed (namely plowing and deicing).
While our outlooks have typically focused on a single day, we’ll attempt to cover this two-day storm in one post. Disruption looks to be more prevalent on Sunday, however Monday is setting up to be the more heavily-traveled day—if patterns hold from previous years, airlines should carry 8-15% more passengers on Monday. We’d lean towards the upper end of that range, as travelers rebook from Sunday to Monday (and if we can influence a couple readers to take advantage of weather waivers, we’d be quite pleased). We’ll tackle the airports in roughly the order they’ll see impacts, starting with ATL.
Recent guidance is trending a degree or so warmer than previous forecasts, which should materially lessen impacts. Rain is forecast to begin tonight, with sleet (i.e. ice pellets) mixing in by early-morning; precipitation may occasionally fall as freezing rain through the morning. Precipitation should become more scattered by afternoon as it lifts north, though some light wraparound precipitation is possible during the evening. Finally, freezing and/or refreezing of any liquid or melted precipitation will need to be monitored into Monday morning, as temperatures are forecast to fall into the upper 20s.
The question for ATL will be how much ice accumulates (probabilities for snow accumulations to reach 1” are less than 5%). If runway closures are not required to treat ice, we think ATL will maintain at least a 98 arrival rate—even with ceilings forecast to lower to 200’ and visibilities reduced to 1 mile. A 98 rate should be sufficient to accommodate demand, which peaks at 74 scheduled arrivals, without air traffic delay. If, however, runway closure are necessary, arrival rates in the range of 26-38 would be possible; in a worse case scenario, a pair of poor braking action reports for the only available runway would effectively close the airport, likely resulting in diversion as well as reactive cancellations.
To that end, it appears airlines are currently thinning their ATL schedules in a more proactive manner (17% as of 3:40 p.m. ET, and climbing it appears). We’d wager this is not in anticipation of air traffic delays but to hedge deicing risk. The TAF2 includes both moderate ice pellets and light freezing rain, which seriously depresses holdover times. If reduced holdover times occur during departure demand peaks (9 a.m. and 11 a.m., most notably), a vicious circle can result wherein taxiing back to the deicing location aggravates congestion and re-joining the deicing queue increases queueing delays.
Airlines were quicker (and deeper) with their CLT reductions, having cancelled 89% of departures tomorrow. Sleet is forecast to start sometime after midnight with freezing rain prevailing by mid-morning. Precipitation should taper off during the evening, however the damage will have been done, with at least 1/4” ice accumulation expected.
Schedule reductions render our typical discussion about capacity and demand somewhat moot; the more worthwhile speculation would likely be directed at the status of the airport. Even if the airport remains open, the depth of cancellations suggests airlines believe conditions will be inoperable for much of the day—it doesn’t appear American plans to operate anything before 4 p.m. We bet American attempts to operate some departures to other hubs later tomorrow (these flights move disrupted passengers out of CLT to be re-accommmodated via another hub) as well as international wide-body departures (rebooking these flights often prove most difficult). Otherwise, we’re not optimistic that American completes much of anything from their domestic spoke or short-haul international schedules.
Continued at 7:30 p.m. ET. After hitting publish mid-post to ensure our outlook for ATL and CLT was timely, we’ll keep moving north along the East Coast.
Low pressure over the Deep South will turn the corner Sunday morning and begin its jog northward. Forecast discussion indicate snow will begin overspreading the region by late morning, however TAFs hold it off until mid-afternoon. Most areas will see a brief period of moderate to heavy snow before a changeover to sleet and freezing rain. Though there’s still some wobble in the low’s track, latest guidance has shifted heaviest snow and best icing westward. Precipitation will wind down late Sunday night.
Moderate freezing rain has been added to the TAF for Dulles (IAD) and Baltimore (BWI), matching Reagan (DCA). Moderate freezing rain looks to set in first at DCA (7 p.m.), followed by IAD (8 p.m.) then BWI (9 p.m. and lasting for only one hour in this last case). Importantly, no holdover time exists for this condition, which generally disallows flights from taking off. We’re guessing it’s for this reason that airlines have begun to take down their schedules at DCA (22% of Sunday departures cancelled), Dulles (21%) and Baltimore (14%).
By design, schedule reductions alleviate demand on the airport, though it’s difficult for us to hypothesize about potential traffic management initiatives until the demand picture settles out. While ice accumulations introduce considerable uncertainty, even high-end snow amounts should not require extensive snow removal efforts. For now, we’ll say this about scheduled arrival demand and airports capacities once precipitation arrives:
28 seems to be the most likely arrival rate for DCA (1 in 3 chance); demand peaks in the 2 and 4 p.m. hour, though is relatively uniform.
64 is a good bet for IAD’s arrival rate (7 in 10); there’s one pronounced demand peak around 4 p.m.
A 28 arrival rate is narrowly more likely than not in BWI; demand peaks in the 6 p.m. hour.
Travelers can monitor how demand takes shape—net of cancellations—via the FAA’s airport arrival demand chart.
Continued at 10:45 p.m. We again took a moment to ensure our Baltimore/Washington information was shared in a timely manner, but we’re picking it up at New York City.
New York City
As the low heads north, winds will shift to the east in the NYC metro area, ushering in noticeably warmer air by afternoon. Precipitation will overspread the area towards Sunday evening, lasting until a dry slot develops over the region on Monday. By the time precipitation begins Sunday evening, temperatures are expected to be in the mid 30s; precipitation may briefly start as snow, however a quick transition to rain is forecast with no more than 2” of snow accumulation. Gusty easterly winds will also be a concern with this system, though strongest winds look to occur overnight. For the purposes of this outlook, we’ve included Philadelphia (PHL) with the NYC metro area: the absence of freezing rain in PHL’s TAF more closely aligns it with NYC than WAS. In terms of differences to NYC airports, snow is forecast to start a couple hours earlier at PHL (around 5 p.m.) and ice pellets are briefly expected to mix with snow (pellets—which complicate deicing—are mercifully excluded from NYC TAFs).
There’s no paywall. Subscribe for free to receive new posts in your inbox.
Cancellations have also been input for NYC airports, though these mostly appear to owe to worse weather on the other end (e.g. CHO, GSO, GSP, PIT, RDU, RIC, ROA). Nonetheless, for Newark (EWR) and Laguardia (LGA), it’s enough to equal a 9-10% schedule reduction (for JFK and PHL, it’s more like 4-6%). With demand unsettled, we’ll again refrain from speculating about traffic management initiatives or delays, but can offer some insights on scheduled arrival demand and airport capacities during Sunday evening:
We’ll set PHL’s arrival rate floor at 32, though it’s hardly unlikely (almost 2 in 5 chance). Demand peaks at 39 in the 6 p.m. hour, though spends the rest of the day at or below 20. We’ll also mention the Philadelphia Eagles playoff game, which may result in a few more sick calls on the margin.
We think 36 is an appropriate floor for EWR (1 in 5 chance to occur; less than 1 in 20 for lower rates), though we’re a bit anxious about a sub-optimal Runway 11 configuration. For the moment, enough of a northerly component is forecast that EWR should hang onto Runway 4L|4R through Sunday (and hopefully open up on Runway 22L|22R on Monday after a predawn wind shift). Demand peaks at 42 in the 7 p.m. and steadily declines thereafter.
We think there’s a 1 in 8 chance for a 26 arrival rate at LGA, but would otherwise bet on 38. Demand peaks at 34 in the 9 p.m. hour then quickly drops off.
For New York-Kennedy (JFK), a 48 arrival rate seems most likely, though a 42 rate is conceivable (at least 1 in 5 chance). Demand just so happens to peak at 42 in the 9 p.m. hour.
Sunday looks to stay dry for BOS, however low pressure will have continued to intensify as it tracks through eastern New York State. Precipitation will reach the area around midnight; here too, precipitation may briefly start as snow or a wintry mix, however all rain is expected by sunrise on Monday. Perhaps most notable is the threat for heavy rain, with available moisture more than 300% of normal for this time of year. The same low-level winds that feed Atlantic moisture into the region will also provide for gusty winds at the surface.
Fortunately, there’s something of a mismatch between the worst conditions (forecast during the morning) and demand (which leans towards the evening). Nevertheless, scheduled arrival demand equals 25 in the 11 a.m. hour and we estimate there’s approximately a 1 in 8 chance that airport capacity is insufficient. Like NYC, we wouldn’t be surprised if there’s a small handful of BOS cancellations Monday morning residual to disruption elsewhere that resolves this potential demand overage.
That’ll do it for updates to this post—we’ll be transitioning our coverage of return travel to Twitter (there figures be plenty of fodder). At this point, only Alaska Airlines and Frontier have elected against issuing a travel advisory for this event. Otherwise, travelers transiting an East Coast airport Sunday or Monday should be able to rebook with no fare difference3. While 2,300 flights have already been cancelled for Sunday, we’d expect this number will continue to climb.
In a note to employees on Jan. 10, United CEO Scott Kirby wrote, “Just as an example, in one day alone at Newark, nearly one-third of our workforce called out sick.”
Terminal aerodrome forecast (TAF) is a format for reporting weather forecast information, particularly as it relates to aviation. TAFs are issued at least four times a day, every six hours, for major civil airfields: 0000, 0600, 1200 and 1800 UTC, and generally apply to a 24- or 30-hour period, and an area within approximately five statute miles from the center of an airport runway complex.
TAFs complement and use similar encoding to METAR reports. They are produced by a human forecaster based on the ground. TAFs can be more accurate than Numerical Weather Forecasts, since they take into account local, small-scale, geographic effects. Source: Wikipedia
Rebooked travel must occur on or before Jan 20 in most cases.