JFK, LaGuardia, and Newark are under ground stops this morning as the Northeast storm wall goes live, with delay programs running through tonight

The 9 AM update: the PROBABLE forecast this morning's issue reported has gone live, with JFK, LaGuardia, Newark, and Teterboro under thunderstorm ground stops and LaGuardia and JFK ground delay programs averaging around an hour running through 6:59 PM Eastern, the FAA's advisory lists a ZNY TMU staffing trigger through 1 PM compounding the thunderstorms, Philadelphia and the DC airports remain at PROBABLE through 10 PM, FlightAware counts 1,211 US cancellations today, and American, Delta, United, and JetBlue all have waivers open.

The disruption this morning's issue flagged as PROBABLE has verified. The FAA's current operations plan, ATCSCC ADVZY 065 (event time 28/1200Z and later), opens with a Northeast Regional Swap Plan: "The NY met airports currently have ground stops for ZAU/ZOB/ZID due to lack of routes," and "the LGA and JFK GDPs were implemented and additional GDPs for the Northeast are impending." The live flightcheck.live feed (FAA NASSTATUS data, checked 8:54 AM Eastern) shows the shape of it.

What's active right now

Ground stops (thunderstorms) are in effect at LaGuardia, JFK, Newark, and Teterboro, expected to lift by mid-morning (flightcheck lists LGA, JFK, and TEB to 9:45 AM Eastern and EWR to 9:30 AM). Behind the stops, ground delay programs are metering arrivals all day:

LaGuardia GDP averaging 1 hour 8 minutes, plus 16-to-30-minute departure delays
JFK GDP averaging 59 minutes, plus 31-to-45-minute departure delays
Newark GDP averaging 1 hour 18 minutes, plus 16-to-30-minute departure delays
Philadelphia GDP averaging 1 hour 27 minutes
Boston GDP averaging 48 minutes
Reagan National GDP averaging 22 minutes

The FAA advisory carries the LaGuardia and JFK GDPs through 2259Z, which is 6:59 PM Eastern. San Francisco also has a separate 46-minute fog ground delay program.

Why: thunderstorms plus the ZNY staffing trigger, again

This is the same two-cause pattern as yesterday, not weather alone. The FAA advisory lists a staffing trigger: "UNTIL 1700, ZNY TMU." That is New York Center's traffic management unit, constrained through 1 PM Eastern. The advisory's narrative ties it directly to throughput: "with the ZNY TMU staffing trigger, reroutes will be slow from ZNY adding to throughput concerns for the airports." New York hotline and diversion recovery are active, and escape routes were published.

The weather side is an unusually strong summer storm. NWS New York's key-messages packet (issued for the event) puts a Flood Watch through 8 AM Wednesday over the tri-state, with 2 to 5 inches of rain on average and isolated totals over 6 inches, rates of 2 to 3 inches per hour, a 5 percent damaging-wind probability (gusts 60 to 70 mph), and a 2 percent isolated tornado probability concentrated over northeast New Jersey into the New York metro. ABC7 New York (updated 8:09 AM Eastern) reports the heaviest morning rain has moved through but additional rounds are expected through the day. Governor Hochul urged caution for the prolonged event. CNN notes the system's strength is closer to an October or November storm than a late-July one, and it is forecast to linger over the region through Thursday.

The numbers so far

FlightAware (as of 9:04 AM Eastern) counts 1,211 cancellations within, into, or out of the United States today and 1,544 US delays, on top of Monday's 1,737 cancellations and 9,034 delays. Travel Market Report (published 7:02 AM Eastern, citing FlightAware) counted over 100 cancellations each at JFK and LaGuardia and another 60 at Newark as of 7 AM. TheTravel (published 6 AM Eastern) reports JetBlue alone had 223 cancellations early Tuesday, most into and out of New York. Because aircraft and crews are held at origin points, the cancellations are cascading into downstream hubs like Atlanta, Charlotte, and Chicago even where the local weather is clear.

What's still ahead today

The FAA advisory keeps the PROBABLE tier (highest confidence) in place through 0200Z, which is 10 PM Eastern, for two clusters:

Philadelphia, Newark, and MMU (Somerville) ground stop or delay program PROBABLE through 10 PM
Reagan National, Dulles, and Baltimore ground stop or delay program PROBABLE through 10 PM

Beyond that, the plan anticipates Charlotte terminal and en route impacts from thunderstorms later this morning, central and south Florida thunderstorm impacts this afternoon, Denver terminal and en route impacts after 4 PM Eastern, and a possible Boston ground delay program after 2 PM (Boston anticipates a single-runway configuration all day with en route and throughput constraints). Northeast AFPs (airspace flow programs) are possible after 2 PM. The next FAA planning webinar is at 1315Z (9:15 AM Eastern).

Chicago's O'Hare and Midway, which absorbed yesterday's near-thousand-cancellation severe-storm day (865 at O'Hare plus 91 at Midway, per NBC Chicago citing the Chicago Department of Aviation), are not in today's terminal active or planned lists and show on time on flightcheck, though they are feeling the downstream ripple from the New York cancellations.

Rebooking basics

All four carriers with major New York and East Coast operations have waivers open. If you are booked through the affected airports, you can rebook without change fees (and in most cases without fare difference, same cabin) within each airline's window:

American Airlines (current as of July 27): BWI, CLT, JFK, LGA, EWR, PHL, IAD, DCA, HPN. Travel July 28, ticket by July 26, rebook July 27 through 30, changes by July 28.
Delta Air Lines: EWR, HPN, JFK, LGA. Travel July 27 through 28, rebook through July 31.
United Airlines: BWI, DCA, EWR, IAD, JFK, LGA, PHL. Travel July 27 through 28, rebook through July 30.
JetBlue: ISP, JFK, LGA, EWR, HPN. Travel July 27 through 29, rebook through August 1.

Check your flight status before leaving for the airport, and rebook through the airline's app or website rather than waiting at the counter, since same-day alternatives disappear fast when a hub goes into a ground stop.