Why tornadoes and hailstorms are more common during the workweek

A new study suggests that in the summertime, tornadoes and hailstorms in the eastern US occur significantly more often during the middle of the week. Why? There's more pollution during the workweek due to commuting and other factors. From National Geographic:

…Moisture gathers around specks of pollutants, which leads to more cloud droplets. Computer models suggest these droplets get lofted up to higher, colder air, leading to more plentiful and larger hail.

Understanding how pollution can generate more tornadoes is a bit trickier. First, the large icy particles of hail that pollutants help seed possess less surface area than an equal mass of smaller "hydrometeors"—that is, particles of condensed water or ice.

As such, these large hydrometeors evaporate more slowly, and thus are not as likely to suck heat from the air. This makes it easier for warm air to help form a "supercell," the cloud type that usually produces tornadoes and large hail...

The pollution-storm pattern is not seen in the western U.S. because the air is too dry and the cloud masses too high and cold for air pollution to influence weather the same way, said study co-author Daniel Rosenfeld, of the Hebrew University of Jerusalem in Israel.

Overall, the research "provides yet another good reason for reducing air pollution," Rosenfeld said.

"Why Tornadoes Take the Weekends Off in Summer"

• [jody]

  Tough luck for the weekend warrior storm chaser.

• [dculberson]

  Are storms possibly 2.5x more common during the work week?

• [NoneofYourPenguins]

  Tornadoes:  Nature’s way of telling you driving to work is wrong.

• [info datatoo]

  there are 2 days in a weekend and 5 days in a work week. That alone makes it more likely

  • [Antinous / Moderator]

    “Work week” and  “weekend”?  How retro.

• [mkultra]

  I suppose it really is asking too much for people to read the damn article before commenting…

  They discovered that tornadoes and hailstorms occurred at a rate of about 20 percent above average during the middle of the week. In contrast, the phenomena occurred at a rate of roughly 20 percent below average on the weekend. The findings proved statistically significant—not just a random pattern—and matched up well with similar cycles seen in other kinds of storms, the study authors say.

  • [bcsizemo]

    Given that they are implying that man made pollution is the case of this increase, it occurring in the middle of the week doesn’t make sense then.  Seeing a spike on Thursday, Friday, Saturday makes more sense as you have Monday through Friday to elevate the pollution levels in the air. 

    What about things like commercial air flights?  Do those increase during the first of the week?  There are a lot of other factors here than people commuting to work Mon-Fri…

    • [Michael Smith]

      Given that they are implying that man made pollution is the case of this increase, it occurring in the middle of the week doesn’t make sense then.  Seeing a spike on Thursday, Friday, Saturday makes more sense as you have Monday through Friday to elevate the pollution levels in the air. 

      Depends on the half life of pollutants in the air.

    • [awjt]

      I know, right?  This conjecture doesn’t fit the Hill Criteria.  You’d think that a mega-dose of would be highest by Friday evening.  

      Unless there is a decay factor, and the decay products from the previous weeks’ pollution don’t reach maximum until the following Wednesday.  Seems less and less plausible. How long we been tracking these things?

• [bcsizemo]

  Statistics, ratios, MATH!  How does it work?!

• [Paul Renault]

  Why?  ‘Cuz workweek days are more common than weekend days?

  If only it were the other way around…

  /off to read the article.

  • [Paul Renault]

    Now that I’ve read the article, I understand why there’s a 20% bump in the graph of tornadoes/hailstorms vs. days-of-week:

    ‘Cuz it’s hump day!

• [Jardine]

  My Dad has plowed snow for 40 years and the pattern he noticed is Thursday nights was when large amounts tended to come down.

  • [Listener43]

    That’s to create long weekends for those who “can’t” make it in to work on Friday.

• [Listener43]

  This observed pattern is precisely reversed in Northern Hemisphere nations where driving is on the left side of the road.
  Clearly, it’s the effect of the spin passed on to the atmosphere by vehicles passing one another in the right-lane-driving mode.
   
  I don’t know why this is such a mystery.

• [Lysy404]

  I get that the incident rates are statistically lower on weekends..(would love to know the stat significance level and if the data were subject to peer review)…the connection to additional pollution is just a theory, even if the computer model seems to supports it…so nothing to see here, keep on moving… 

  • [MythicalMe]

    In the way you’re wording it’s a hypothesis.

• [Incipient Madness]

  Northeast Houston gets more rain and lightning strikes than the rest of the area  because the sea breeze and heat island effect create a huge pillar of polluted air. Some summers, 2006-2008 for example, there is even a predictable “rush hour rinse’ of local thundershowers. something changed in 2010 and we had a winter drought followed by the hottest and driest summer ever. Very few heat island rains, and almost no regular rain.

  But I can attest that the rush hour rinse is quite real many summers and is linked to pollution and the heat island effect. It seems plausible that similar events occur elsewhere, even to the point of creating tornadoes and possibly snowstorms as another commenter suggested.

• [Daemonworks]

  Obviously caused by all the hot air generated by people working in sales/marketting.

• [Guest]

  I currently, and have for thirty years, live in the Washington, DC metropolitan area.  

  Up until fifteen or so years ago, it seemed to me and to others I have spoken with, a majority of our weekends had more rainy days than the days Monday through Friday. Almost as if it rained most weekends.  I seem to remember this being attributed to the air quality that moved via the Jet Stream, from the “Rust Belt” to our area. 

  I say up until fifteen years ago, because air quality has improved, most likely attributed to tighter vehicle emissions standards and a reduction in industrial output from that area.

• [Sencho]

  Oh good Lord, not this junk science again. 

  Firstly, the conditions for tornadoes and hailstorms require a certain range of winds, moistures, and temperatures on a regional scale.  Any particulate emissions from the work week travel and industry are beyond trivial in terms of their weight of impact.

  Secondly. this hypothesis would mandate that areas downwind of large cities would be most prone to these storms.  Yet Tornado Alley is known for an absence of large cities – and industry. 

  All this ‘study’ shows is that some researchers are corrupt enough to rehash this oft-disproven hypothesis for the sake of quick funding.  Pathetic.