Giant Cloud Leaves Commuters Baffled

April 18, 2008 9:34 AM

You are not my meteorologist but . . . There are clouds and there are clouds, I'd never seen one like this before, what kind was it?

Last night as my SO and I were going to dinner, we saw a vast wall of cloud to the east. It looked (almost disturbingly so) like a giant white wave or a concave cliff face of extreme height. It stretched from North to South and took up the entire horizontal horizon and was (I'm guessing) a few thousand feet high.

Place: Western MetroBoston between RT 2 and I-90 along I-95.
Time: 7:00 pm-ish.
Weather: Otherwise clear and mild (50s? Farenheit)
Wind: None of any significance.

(Sorry, still don't have a camera phone so no pics.)

posted by MasonDixon to science & nature (12 comments total)

my unexpert opinion - the backside of a thunderstorm. atleast when you see something like that in oklahoma that is what you are looking at.
posted by domino at 9:49 AM on April 18, 2008

Just guessing the only strange cloud I know of -- mammatus?
wikipedia article and flickr photos
posted by spectracide at 9:57 AM on April 18, 2008 [1 favorite has favorites]

A type of arcus cloud? Those are associated with thunderstorms, though.
posted by zsazsa at 10:05 AM on April 18, 2008

I saw the arcus on wikipedia, but it does seem to be more closely associated with thunderstorms and it has been mild here the past few days.
posted by MasonDixon at 10:13 AM on April 18, 2008

Probably not a cloud, per se, but a fog bank.
posted by Cool Papa Bell at 11:45 AM on April 18, 2008 [1 favorite has favorites]

A wall of cloud, you say? Could it have been a wall cloud? ((images.) Or perhaps a shelf cloud ((images.)? (I think these are types of arcus clouds.)
posted by PercussivePaul at 12:06 PM on April 18, 2008

Yeah, going by your description, I'd say probably a Shelf, Roll or other type of Arcus.

There is a good picture of a Shelf Cloud at the bottom of this page
posted by ArgentCorvid at 12:40 PM on April 18, 2008

Roll cloud (wikipedia), or shelf cloud as PercussivePaul suggests). Did you mean Rte. 495? I used to see those with some regularity on my commute between Boston and 495 (that is, of weird clouds those were the ones I saw most often). I'm not sure what the geographic feature is around there that might contribute to that being a common phenomena. Perhaps it's just that 495 runs N-S there like much of the weather and so it's easier to see it over the highway.
posted by cocoagirl at 12:47 PM on April 18, 2008

The shelf clouds are common with changing weather aren't they? The description sounds like a gravity wave. here is an example of gravity waves in the atmosphere rolling by. It's just like an ocean wave but a heckuvalot bigger and you can see them because as the air crests, it crests into a colder layer making the vapor condense into the cloud until the air goes back into its native or lower layers of air.
posted by Phantomx at 8:06 PM on April 18, 2008 [1 favorite has favorites]

Hey, MasonDixon, would this be the cloud you were talking about? (I searched Flickr for photos tagged "Boston" and "clouds," uploaded in the last week.)

If so, maybe it'll help for ID purposes. If not, it's still remarkably pretty!
posted by kwaller at 5:50 AM on April 19, 2008

That's the very cloud of which I am speak!

I've been out of town so sorry for not getting back to this thread sooner.
posted by MasonDixon at 3:01 AM on May 4, 2008

make that "which I speak" no coffee yet this morning
posted by MasonDixon at 3:02 AM on May 4, 2008