<p>You were most likely seeing lightning (to be sure, a date/time and your location would be necessary).  Lightning can be visible from quite a distance and storms can be incredibly active with lightning within the clouds and from cloud-to-cloud.  Given a large distance and being inside a (relatively) loud airplane cabin it is no surprise that you couldn't hear the thunder associated with the lightning flashes.  </p>

CC BY-SA 3.0
2015-03-02T16:24:42.580Z
2015-03-02T16:24:42.580Z
casey
<p>While I wouldn't rule out that you were witnessing distant lightning lighting up the clouds below, or at some distance anyhow, there is also the possibility of the flashes being <a href="http://Upper-atmospheric_lightning">upper-atmospheric lightning</a> such as <a href="https://en.wikipedia.org/wiki/Sprite_(lightning)">Sprites</a>. The half hour duration of the phenomena seems quite a long duration if we assume a plane in flight would cover somewhere about 300 miles in this time. So another possibility could be <a href="https://en.wikipedia.org/wiki/St._Elmo%27s_fire">St. Elmo's fire</a> and another possibility would be wing condensation flashes over the wings, reflecting the light from inside the plane. <a href="https://www.youtube.com/watch?v=N68rZZdhGvU">A youtube video of the effect at take off in daylight</a>. Or else possibly a cloud situation that reflected back the plane's own flashing exterior lights for this portion of the journey.</p>

CC BY-SA 3.0
2016-12-05T13:23:57.007Z
It can't have been upper-atmospheric lightning, which (as the name suggests) occurs in the upper atmosphere ([above 20 km or so](https://en.wikipedia.org/wiki/File:Upperatmoslight1.jpg)). OP estimated the altitude of the flashes at around or below 10 km (35,000 feet), making "normal" lightning a far more likely candidate.
Pont
CC BY-SA 3.0
2015-03-03T04:15:32.127Z
While airliners do cover a lot of distance in a half hour, some lines of thunderstorms are very long. Also, you can see things a very, very long way away (well over 100 miles) from the altitudes that airliners fly, even more so when what you're looking at is also tens of thousands of feet up.
reirab
CC BY-SA 3.0
2015-03-03T14:32:24.690Z
Doubtful it was St Elmos fire.  I've seen up that up front (windscreen and nose) and its different than lightning flashes.  Strobe lights in the clouds will produce very regular flashes (but a good crew will turn them off in this case).  I'd be jealous if he was seeing sprites, I never managed to catch a glimpse in 2500 hours at 37,000 ft.
casey
CC BY-SA 3.0
2015-03-02T20:43:07.083Z
2015-03-02T20:43:07.083Z
Siv
<p>On a recent, late-evening flight from New York City to San Fransisco, I was seated on the right side of the plane. We were flying over lake Michigan - about 2 hours into the flight. When we were over the mid-west I looked out of the window and could see these continuous flashes in the sky. At first I thought it was lightning, however this continued for almost 30 minutes or so and seemed to be silent too. What is this phenomenon?</p>

CC BY-SA 3.0
2016-12-05T19:18:53.283Z
The strobe of another plane or the one of your plane reflected off ice or clouds if at all regular.
dlb
CC BY-SA 3.0
2015-03-02T21:59:49.707Z
Was the flashing very regular, or sporadic (random)?
Floris
CC BY-SA 3.0
2015-03-03T05:17:15.793Z
I wonder about what @Floris asked because when I saw this question it sounded like the description of an airplane strobe light.
Selali Adobor
CC BY-SA 3.0
2015-03-03T05:21:20.067Z
It was definitely not a strobe light or even St. Elmo's fire. It was at a substantial distance from the plane. Assuming a cruising altitude of about 35k feet, I was not looking up - but probably same level or a little down.
TV Mohini
<atmosphere><lightning>
Weak flashes of light in the sky
TV Mohini
# Weak flashes of light in the sky

(Asked by: username_0 on 2015-03-02)

On a recent, late-evening flight from New York City to San Fransisco, I was seated on the right side of the plane. We were flying over lake Michigan - about 2 hours into the flight. When we were over the mid-west I looked out of the window and could see these continuous flashes in the sky. At first I thought it was lightning, however this continued for almost 30 minutes or so and seemed to be silent too. What is this phenomenon?

**Tags:** atmosphere, lightning

> **Comments:**
> **username_2**: Was the flashing very regular, or sporadic (random)?  
> **username_3**: I wonder about what @username_2 asked because when I saw this question it sounded like the description of an airplane strobe light.  
> **username_0**: It was definitely not a strobe light or even St. Elmo's fire. It was at a substantial distance from the plane. Assuming a cruising altitude of about 35k feet, I was not looking up - but probably same level or a little down.  
> **username_1**: The strobe of another plane or the one of your plane reflected off ice or clouds if at all regular.  

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## 2 answers

### Answer by username_4 on 2015-03-02. Score: 15

You were most likely seeing lightning (to be sure, a date/time and your location would be necessary). Lightning can be visible from quite a distance and storms can be incredibly active with lightning within the clouds and from cloud-to-cloud. Given a large distance and being inside a (relatively) loud airplane cabin it is no surprise that you couldn't hear the thunder associated with the lightning flashes.


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### Answer by username_5 on 2015-03-02. Score: 6

While I wouldn't rule out that you were witnessing distant lightning lighting up the clouds below, or at some distance anyhow, there is also the possibility of the flashes being [upper-atmospheric lightning](http://Upper-atmospheric_lightning) such as [Sprites](https://en.wikipedia.org/wiki/Sprite_(lightning)). The half hour duration of the phenomena seems quite a long duration if we assume a plane in flight would cover somewhere about 300 miles in this time. So another possibility could be [St. Elmo's fire](https://en.wikipedia.org/wiki/St._Elmo%27s_fire) and another possibility would be wing condensation flashes over the wings, reflecting the light from inside the plane. [A youtube video of the effect at take off in daylight](https://www.youtube.com/watch?v=N68rZZdhGvU). Or else possibly a cloud situation that reflected back the plane's own flashing exterior lights for this portion of the journey.

> **Comments:**
> **username_7**: While airliners do cover a lot of distance in a half hour, some lines of thunderstorms are very long. Also, you can see things a very, very long way away (well over 100 miles) from the altitudes that airliners fly, even more so when what you're looking at is also tens of thousands of feet up.  
> **username_4**: Doubtful it was St Elmos fire.  I've seen up that up front (windscreen and nose) and its different than lightning flashes.  Strobe lights in the clouds will produce very regular flashes (but a good crew will turn them off in this case).  I'd be jealous if he was seeing sprites, I never managed to catch a glimpse in 2500 hours at 37,000 ft.  
> **username_6**: It can't have been upper-atmospheric lightning, which (as the name suggests) occurs in the upper atmosphere ([above 20 km or so](https://en.wikipedia.org/wiki/File:Upperatmoslight1.jpg)). OP estimated the altitude of the flashes at around or below 10 km (35,000 feet), making "normal" lightning a far more likely candidate.  

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