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  • Writer's pictureTim Donohue

[Thanksgiving 2021] Sunday Nov 28 first look

We hope readers enjoyed their Thanksgiving celebrations! If you flew somewhere on Wednesday, you participated in the busiest air travel day since the before times - more than 2.3 million passengers were screened by TSA. Sunday figures to be even busier and we're eager to see if it surpasses the 2.5 million mark. Weather was generally cooperative for go travel ahead of the Thanksgiving, though we're watching for potential impacts to return travel on Sunday: a clipper moving across the Great Lakes and the development of a strengthening secondary low off the Northeast coast could produce some snowflakes for a broad swath of the country. While impacts should be modest, this would be the first winter weather test for many of the airlines and 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. We'll frequently refer to airport arrival rates, queuing delays in the airspace and different tools to distribute those delays. If these concepts are unfamiliar (or intimidating), we'd encourage you to check out our explainers.

Before we dive into winter weather impacts, we want to mention another atmospheric river event that will deliver a round of moderate to heavy rainfall to Seattle (SEA). Metro Seattle should be spared the worst of this event, however an arrival rate reduction is nonetheless likely. We think there's at least a 1 in 5 chance that the arrival rate falls into the 30's. Something like a 38 rate would be most problematic in the 10 a.m. hour, when 48 flights are scheduled to arrive, though overages would also exist in the 2, 6 and 8 p.m. hours. We'll refrain from speculating on types of traffic initiatives (and shape of delays) until the weather forecast is refined, but arrival delays of at least 20 minutes are probable if a 38 arrival rate is delivered for much of the day. One qualification: our modeling is aimed at tackling arrival delays, though there's a strong correlation to departure delays (albeit with some lag and/or possible alleviation).

Let's move on to the possible winter weather impacts, starting with Detroit (DTW). From late Saturday through Sunday, storm totals at DTW look to be around 2-3", with heavier activity focused on late Saturday. Though we note unusually high uncertainty, Sunday accumulations are currently forecast around half inch, which should not require runway closures for snow removal. Barring such closures, 60 represents a reasonable floor for DTW's arrival rate on Sunday; arrival demand peaks at 37, so we're quite confident DTW air traffic delays will be virtually zero. While delays resulting from a capacity/demand imbalance are unlikely, de-icing delays should be expected if snow is actively falling. And of course, delays resulting from aircraft servicing, airline staffing, network effects, etc. are also always lurking (and not included in our modeling).

We'll keep moving east and stop in NYC, where we'll cover Newark (EWR), Kennedy (JFK) and LaGuardia (LGA). Model guidance has been hinting at less precipitation and a generally weaker system for the Tri-State area, though here too there is a fair amount of uncertainty. In terms of precipitation type, light snow is possible Sunday morning before a changeover to plain rain. As the aforementioned secondary low develops off the coast and pulls in colder air, a changeover back to snow is possible Sunday night. Snow accumulations are forecast to be minor (i.e. high end amounts are less than quarter inch), so, like DTW, we shouldn't have to worry about the impacts of snow removal from runways. Also like DTW, de-icing delays should be expected while snow is actively falling (snow is more likely at EWR and JFK than it is at LGA). Separate from snow, we're also keeping an eye on ceilings. At EWR, we think there's around a 1 in 10 chance that the arrival rate falls below 40 on account of cloud bases; airport arrival demand is at or above 40 in three hours (including a peak of 43). We put similar chances (1 in 10) around LGA delivering a 38 arrival rate, however demand exceeds that low-end rate in just one hour (40 scheduled arrivals in the 1 p.m. hour). At JFK, we think 44 is a reasonable arrival rate floor and demand peaks at 41.

If a 38 arrival rate is realized during EWR's peak demand periods, arrival delays would average around 10 minutes. On account of some scheduled bunching in the back half of the 1 p.m hour at LGA, a 38 rate could briefly create delays of around 20 minutes during the early afternoon; otherwise delays at LGA would be largely imperceptible even at a 38 rate. Given no predicted demand overages at JFK, air traffic delays should be virtually zero.

Up at Boston (BOS), much of Sunday should be tranquil as the secondary low treks north along the Mid Atlantic coast. By Sunday night, however, the low should be off the New England coast and chances for precipitation increase. Uncertainty is even higher for BOS, as some outlier models develop an entirely new feature that could increase snowfall amounts. At this point, uncertainty is too high to forecast anything other than a dusting: BOS will garner more than its fair share of tomorrow's update. In terms of capacity and demand, we'll note 32 is a serviceable arrival rate floor in the absence of snow removal efforts and that scheduled arrival demand peaks at 31. It seems likely evening departures from BOS will experience de-icing delays... and for the moment, that will be the extent of our BOS predictions.

Reasonable worst case outcomes are not particularly alarming at any of the airports we covered - coupled with unusually high uncertainty, we'd recommend against rebooking at this time. Before we wrap up this outlook, we'll also share a couple competing themes that will likely nudge delays on Sunday. Airlines and airports typically over-prepare for the first snow event of the season, which should provide a degree of insurance against high end snow amounts; unfortunately, we'd bet airlines will see an uptick in sick calls for baggage handlers on Sunday (watching football on a couch will prove too attractive relative to a cold, wet shift for some), which will exacerbate existing staffing shortages. Though the wheels shouldn't come off as a result, we think the influence of staffing outages narrowly wins out.

We'll be back tomorrow, when we'll be most focused on SEA, EWR and BOS!


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