ROANOKE, Va. – The same system that brought wide spread rain to southwest Virginia Thursday night helped slingshot a passenger plane across the Atlantic Friday night. The jet stream is one of the driving forces behind our weather. It is a fast-moving ribbon of air that resides up where jet aircraft fly, hence the name jet stream. It is the dividing line between warm and cold air and the pathway in which storms travel.
The jet stream is fueled by temperature differences. The bigger the difference, the stronger the jet stream. This is why the jet stream is much stronger in winter than in the summer. Oftentimes in winter it can be in the 80s in Florida and well below zero in the Upper Midwest or Canada.
In winter, the winds within the jet stream can be well over 200 mph, as was the case Friday night. The temperature and pressure gradient (difference) was extreme in between the Bermuda High and Icelandic Low fueling the intense winds at about 35,000 feet.
KLM Flight 644 took off just before 9:30 p.m. Friday, Feb. 7 from New York’s JFK airport en route to Amsterdam. A little more than an hour into the flight, the ground speed reached more than 800 mph! At 11:10 p.m. as the plane was flying over Newfoundland, the ground speed reached 821 mph. The filed speed for the flight was 564 mph.
It is important to note that ground speed is different than air speed. While technically the plane was moving faster than the speed of sound from a ground perspective, it is air speed that matters for breaking the sound barrier. The air speed, or how fast the plane was going on its own power, was about 500 mph, more than 250 mph less than the speed of sound. Think of ground speed as walking on an airport people mover. If you maintain the same walking speed as you enter the people mover, you yourself aren’t moving any faster, but you are moving faster relative to the objects you pass by.
With a filed aircraft speed of 564 mph, KLM Flight 644 would have been pushed along by a tailwind of 257mph! The flight arrived in Amsterdam 1 hour and 17 minutes early!
Data from a weather balloon launch Friday even in Stephenville, Newfoundland, near where the plane flew over, showed wind speeds of 235 mph at jet stream level. Circled below are the recorded wind speeds from the instruments on the weather below.
The wind barbs, which show the wind direction and speed show winds out of the southwest and four triangles. Each triangle represents wind speeds of 50 knots. Since there are four triangles, you get 200 knots of wind. The raw data shows 205 knots of winds over Newfoundland equaling 235 mph.
While definitely not always this extreme, pilots flying from west to east, the typical motion of the jet stream, locate the jet stream on a daily basis to help give them a boost. That is why oftentimes you may arrive early to your destination if you were flying from say St. Louis to New York. If you were flying from Orlando to Seattle, the flight time is typically a little longer since you are fighting the jet stream as a headwind. I can imagine the flight back from Amsterdam encountering that head wind took just a little bit longer.