Snow long, farewell ...

October 26, 2011 3:26 PM

Why do snowstorms last so long? We live in the Denver area and it snowed for 18 hours, from 9 PM last night to 3 PM this afternoon. My wife asked me why it never rains for that length of time. I muttered something about convection in the summer, then stopped when I realized I didn't know what I was talking about.
posted by lukemeister to science & nature (11 answers total)

I don't have a scientific answer for you either way but, anecdotally, I can tell you that I always wonder why snowstorms don't last longer. Here in Boston it often rains for days at a time but it rarely snows (really snows) for more than 12 hours at a stretch, in my experience.
posted by lydhre at 3:29 PM on October 26, 2011 [4 favorites]

I think your premise is flawed. I live in Chicago, and I've never noticed a length-of-storm difference between one kind of precipitation to another. In my experience, I think there are just as many short, scattered snow falls as there are short, scattered rainfalls, and same with long, drawn-out storms.

I also grew up in a perpetually hurricane-affected area of the country, and holy balls I can tell you that rainstorms can last a long time. 18 hours is nothing.
posted by phunniemee at 3:36 PM on October 26, 2011

I think this is less about snowstorms lasting a long time and more about the abnormally short rain patterns in Denver. Perhaps surprisingly, Colorado actually has a monsoon season, lasting from June through August/September. That monsoon weather brings the predictable pattern of clear blue skies all morning, fast build-up of clouds around 2pm, an hour or two of furious rain, then clear skies again by 5pm.

In most of the rest of the country, it doesn't rain like this in short little bursts. "Normal" rains (that is, ones caused by low pressure systems slowly moving into and then out of the area) last about as long as the snowstorm did last night: about 18 hours.
posted by iminurmefi at 3:43 PM on October 26, 2011 [10 favorites]

Check out coloradopowderforecast. He does a great job of explaining it. Basically with this storm there were winds coming from the east and they met up w/ a very wet storm coming from the pacific and it slowed the storm down greatly. This is why the foothills saw more snow than loveland and abasin. Once the storm came over the continental divide it ran into those winds slowing it down greatly.
posted by no bueno at 3:46 PM on October 26, 2011

seconding iminurmefi- this is something about Denver's seasonal precipitation patterns, not actual rain/snow differences. If you lived in northern Michigan, you could wonder why snow can fall for only a few minutes at a time, but spring rains can last a week.
posted by rockindata at 5:26 PM on October 26, 2011

Confirmation bias, I presume. Take the 2009 Atlanta Floods, when it rained here continuously for over a week. Rain storms last just as long as snow storms. It's just a different kind of precipitation.
posted by litnerd at 5:46 PM on October 26, 2011

Yeah I think the folks up thread talking about your premise being flawed are right. I was born and raised in Chicago and have either lived or spent significant amounts of time in Detroit, Boston, Albuquerque, Los Angeles and now here in Denver.

When I moved to Boston is rained for what seemed like weeks. When I lived in Albuquerque I would miss entire rain storms when stopping into the grocery store in the afternoon.

Any high desert place with a monsoon season AND a winter probably has short rain storms as compared to places with more "normal" weather.

Also - I seem to recall a rain storm in the last 6-8 weeks that did last for an entire day+, but I'd be hard pressed to give you a date on that.
posted by FlamingBore at 6:03 PM on October 26, 2011

I am not entirely sure, but I grew up in Buffalo, with its snowy reputation and all and lived through the Blizzard of '77 and everything, so I kind of know from snowy. There, the deal is the lake effect, which I am amazed by every time I drive home during a snowstorm to find Toronto bone-dry. But I think, as I recall from being really surprised from learning waaaaay back in elementary school that Denver can be even snowier, that Denver's snowy botheration is due to upsloping.
posted by peagood at 6:15 PM on October 26, 2011

I don't think it's about snowstorms per se. Like lake effect snow in upstate NY, where storms just stall out and keep going over lakes. In my experience, Boston is much like lydhre says: it rains for days much more frequently than it snows for days. So, it's a Denver thing.
posted by J. Wilson at 6:16 PM on October 26, 2011

Thank you all for correcting my misconceptions. Any suggestions for further reading on rainstorms and snowstorms? (Technical literature is OK.)
posted by lukemeister at 8:40 PM on October 26, 2011

The Front Range of the Rockies are a bit of a special case because the drivers for snow and rain are different. Almost all precipitation of any type happens when moist air rises, expands, and cools down so that it becomes saturated. As others have mentioned for summer rain the driving force that gets the air rising is solar heating of the ground. Once the sun starts setting solar heating diminishes and convection quickly ends.

Snow in Denver is more often powered by orographic lifting. An east wind across the Plains has nowhere to go up up once it hits the mountains. That type of situation can happen for a much longer time scale than afternoon heating by the sun. Depending on the temperature, though, the precipitation could just as easily be rain instead of snow.

Other locations will have different predominant means for getting air to rise and cool and the types of forcings will also vary by season.
posted by plastic_animals at 5:18 AM on October 27, 2011 [2 favorites]