This might be a good time for those still shopping for next year's flights to take a look.
For about two weeks I've been watching fares on this itinerary:
April 8 Washington DC to Madrid (one stop; apparently no non-stops in April)
August 22 London to Washington DC (non-stop)
There weren't a lot of attractive options for me since I avoid small airlines, tight connections, and connections in the US. My favorite possibility was KLM+KLM outbound (change in Amsterdam) and Virgin Atlantic on the return. The price of the routing was about $900. I checked daily, hoping to buy on a dip, but the price didn't vary by more than a few dollars. I thought perhaps something interesting would happen over the Columbus Day weekend, but no. I hated the thought of paying so much from the east coast; $900 felt a bit pricey for such an early purchase. Still, holding off on that peak-period August return felt pretty risky.
When I checked late last night (Tuesday), I saw a bunch of sub-$700 fares. When I dug into them, they were Basic Economy and wouldn't end up that much cheaper than my preferred routing, plus they had less attractive schedules. I suspect the airline(s) had just added the Basic Economy option, so those pre-existing routings had jumped to the top of the list on Google Flights. So no real help for me there.
But it occurred to me that the mere presence of those apparently-lower fares might have an impact on other offerings for my route, so I decided to see what happened in the next 24 hours or so.
When I checked today, my preferred flights were priced at $594 (bought through Delta). That includes one checked bag but not seat selection. Choosing the transatlantic seat cost me $23. I'll let the other two seats ride until check-in time, I think. I believe Virgin Atlantic's seat-selection fee is a lot higher.
Fares are very specific to origin, destination and date, and I may have been unusually lucky, but if you're in the market, price out your itinerary today.