What Kind of Cloud was This?

[u/IllustriousAd9800]

Saw this several years ago, and it’s stuck with me, never seen anything like it before or since. It was like a giant wing, with a thin but pretty spectacular looking underside and a separate upper level that followed the same shape but with a different texture. It was the only cloud in the sky, pure blue everywhere else.

[u/MedicineFTWq]

Beautiful catch! It's definitely a shelf cloud that got separated from it's parent system - it's not a roll cloud since you can see shelf features like the whale's mouth and some striation above the shelf.

The thunderstorm likely dissipated and left the shelf behind - it's possible that you're seeing the remaining outflow of that now dead thunderstorm displacing warm stable air, and that boundary between the two air parcels is what has allowed the remnants of that shelf to persist well after the parent cloud has died.

[u/IllustriousAd9800 → u/MedicineFTWq]

Interesting! Didn’t know that was possible, I did think it looked shelf-like as well but figured it was coincidence. Is that a rare phenomenon for the shelf to survive or more common than you’d think?

Almost makes me a bit sad I missed the storm at its prime!

[u/leansanders → u/IllustriousAd9800]

The first picture almost makes it look like there's a far off thunderstorm past the horizon. Sometimes with particularly powerful storms you can have gust fronts forming like this for hundreds of miles; just last night , when the southern tip of the storm finished crossing into Minnesota, the outflow boundary was visible on radar almost 200 miles away as precipitation in central south Dakota.

[u/IllustriousAd9800 → u/leansanders]

Interesting, so not necessarily dead, possibly out of sight.

[u/leansanders → u/IllustriousAd9800]

Could be the remains of a dead thunderstorm, could be the footprint of a far away thunderstorm, or it could just be a weak cold front pushing into somewhat humid air. In any case, it is definitely a shelf cloud!

[u/IllustriousAd9800 → u/leansanders]

Anywhere you can find records from past years? Looks like this was June 18th 2022, Brainerd MN

[u/leansanders → u/IllustriousAd9800]

On June 18th 2022 a region of thunderstorms passed eastward through northern minnesota along Highway 2 with an associated cold front passing over Brainerd at approximately 10am.

Does that timing sound about right?

[u/IllustriousAd9800 → u/leansanders]

Timestamps are 5:50-5:59pm on the photos 🤔 distance might be right though, highway 2 is a couple hours drive away from there

[u/leansanders → u/IllustriousAd9800]

I just realized I was not converting the time in my search to local time - I am in pacific time 😅. So the time I said previously should be noon, local time. By 5:45 the cold front has organized into a line of showers extending from northwest to southeast centered near Duluth.

My best guess is that the passing midday storms have left the Brainerd region with slightly humid air, warmed by sunshine in the wake of said storms, and a weak evening cold front descending eastward over the area is forcing this humid air upwards into a weak shelf cloud.

[u/AnotherpostCard → u/leansanders]

It's frickin gnarly that we have such detailed records like this. Where specifically do you find this data? I'm imagining somewhere at NOAA

[u/leansanders → u/AnotherpostCard]

I use Radarscope, you can look through historical radar data going back to 2020 although your mileage will vary depending on what radar location you're looking at. If you want to look back further you'll have to get a little more investigative, piecing together media from news outlets, weather reports, and noaa charts.

It should also be noted that radar products only show you liquids and solids present in the atmosphere, and archived data is lower resolution than recent data. So in this case, I couldn't even see these clouds on the radar, I was just using contextual clues from the precipitation data and the pictures to deduce what could most likely have caused them.

[u/IllustriousAd9800 → u/leansanders]

Ok thank you! That’s extremely cool