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Posted at 1:00 PM ET, 02/11/2010

Wind chill: Its history & effect on people & things

By Don Lipman

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National Weather Service wind chill chart.

He said to the TV reporter: "...with the high winds and the wind chill factor, I'm servicing many more cars than usual due to dead batteries." "He" was a tow truck driver helping a driver get her car started during a recent cold spell. After watching that exchange, I was prompted to write this article.

Was he right? Do batteries really weaken or go dead more easily when there is a very strong wind chill factor? The larger question really is whether the wind chill factor affects inanimate objects at all.

A little history first. In 1945, Antarctic explorers Paul Siple and Charles Passel devised an index that attempted to compare how cold we feel at various temperatures and wind speeds with how cold we feel at the same temperatures in still air. This original wind chill index languished, more or less, until it gained great notoriety during the famous (or infamous) "Ice Bowl" Championship Game between the Dallas Cowboys and the Green Bay Packers in Green Bay in 1967. With a game-time temperature of -13F and a wind chill factor of -48F (according to the original index), it was one of the two coldest pro football outings ever staged. (The other was the 1981 AFC Championship Game between the San Diego Chargers and the Cincinnati Bengals, which was played in -9F weather with a wind chill of -59F (original index).

Since those games, the wind chill index has been revised at least once to reflect the fact that the National Weather Service believes we don't feel as cold under wicked winter winds as previously thought. (The earlier game is now considered to have been played in a -36F wind chill, and the 1981 game in a -37F wind chill -- still not exactly a walk in the park.)

Although the wind chill index has been relaxed, the media has not relaxed (in my humble opinion) its overemphasis of it -- almost to the exclusion of the actual air temperature. I suppose it sounds much more dramatic to say that it feels like 17F when it's really 35F. Furthermore, since there are several mitigating factors that lessen the impact of the wind chill factor -- e.g., warm clothing, sunshine, etc. -- the actual index should only be used as a rough guide anyway.

By the way, I believe the wind chill factor was zero on Super Bowl Sunday at Miami's Dolphin Stadium. That's zero as in no wind chill factor, as the high temperature was 66F and I saw no reports of frostbite. (The average high in Miami for the date is 77F.)

So what about the wind chill factor's effect on inanimate objects? It turns out there is none, unless you consider the following as an "effect": Wind will cause an exposed warm machine, such as a car engine, to cool more rapidly (down to the ambient air temperature) once shut off, and once turned back on, the engine will take longer to reach normal operating temperature. Although not a heating engineer, I'm told this is because in both instances, heat is removed more rapidly than otherwise would be the case.

As for your car's radiator, obviously follow the manufacturer's recommendations, but as long as the air temperature is above freezing, the radiator mixture won't freeze anyway, no matter how low the wind chill factor gets. And that car battery?... yes, it's more difficult for the battery to start the engine in cold weather because of a slower chemical reaction (thus the importance of cold cranking amps), but the wind chill is irrelevant.

However, if one were to park a car outside under severe wind chill conditions and return to the car, say, in two hours, I suppose the battery would have cooled down to the air temperature more quickly than otherwise, making it more difficult to start with a weak battery.

Above all, please don't risk frostbite by going unprotected, especially when temperatures and winds combine for frostbite times of 30 minutes or less,, as showin the wind chill chart at the top of this post. I know our colleague, Ann Posegate, who recently spent time in Antarctica, was well protected, as she says she was wearing 24 pounds of wool, polar fleece, polypropylene, leather and plastic -- and it's summer in Antarctica!

By Don Lipman  | February 11, 2010; 1:00 PM ET
Categories:  Lipman  
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Comments

"please don't risk frostbite by going unprotected"

Sounds like something the First sergeant said before we went into town on Friday nights...

Posted by: wiredog | February 11, 2010 1:14 PM | Report abuse

FIRST!

Posted by: HolyMoley | February 11, 2010 1:53 PM | Report abuse

HolyMoley...

I thought you were off to go enjoy the day??

Lol!

Posted by: Alexandria2009 | February 11, 2010 1:57 PM | Report abuse

Thanks for this informative piece. Whether or not wind chill affects inanimate objects like car batteries, I will always remember the chance I had once in Minnesota to help a friend recharge a 'dead' battery in temperature that was apparently 34 below in terms of wind chill. At that moment, I wasn't thinking of wind chill's effect on the battery -- just on me! :)

Posted by: krosseel | February 11, 2010 2:17 PM | Report abuse

To be honest, Don, I felt colder walking around in D.C. over the past few days than during my time in Antarctica last month! Even if one doesn't have top-of-the-line clothing/gear for this weather, wearing lots of layers is still the best defense against windchill.

Posted by: Ann-CapitalWeatherGang | February 11, 2010 2:18 PM | Report abuse

Only in Washington: 100 Iranian "Democracy Now" protestors marching up Wisconsin Ave. a short time ago. Gotta' admire their grit!!

Snow Fair Entreaties: Please Snow Fairy, bring 4.1" more snow to DCA this season so we can hit 60". They scoot 'til next December.

Posted by: JerryFloyd1 | February 11, 2010 2:19 PM | Report abuse

@Ann

I'd be interested in hearing about Antarctica and your experiences with wind chill, etc. there.

Posted by: krosseel | February 11, 2010 2:19 PM | Report abuse

...The reason being that I had to give all of my gear back after the trip.

Posted by: Ann-CapitalWeatherGang | February 11, 2010 2:20 PM | Report abuse

@JerryFloyd1

Is it OK if the Snow Fairy brings the snow in two or three increments?

Posted by: krosseel | February 11, 2010 2:23 PM | Report abuse

Glad to see this article! People have always told me that 'wind chill' means nothing to 'hardware', and, as an engineer with knowledge of fluid and thermodynamics, I've always said 'not so'!

It's exactly as stated in this article: wind blowing cold air across your car, engine, whatever, will cool it down more quickly than if it was sitting where there was no wind. Not exactly the same as the 'wind chill' effect on people or animals, and it won't ever end up colder than ambient, but don't tell me 'no effect'! :)

Posted by: leesweet | February 11, 2010 2:25 PM | Report abuse

Question then: It's 33 degrees with a strong wind blowing. Can you get frostbite?

Presuming that the wind will cool your skin more rapidly than 33 w/ no wind, but that the air is not cold enough to freeze.

However, could evaporative effects actually give you frostbite in 33 degree air?

Posted by: AndrewRockville | February 11, 2010 2:34 PM | Report abuse

Just wanted to share this with you all: Snowmen Protesters in DC

Posted by: joelhousman | February 11, 2010 2:34 PM | Report abuse

@krosseel; don't care how the Snow Fairy sprinkles her snowdust, long as it ends up being 60". Accuweather is calling for 3.2" inches on Monday.

Accuweather's list of region totals for yesterday's storm at
http://www.accuweather.com/news-story.asp?partner=accuweather&traveler=1&zipChg=1&article=1

East Nantmeal, Pa., north of Wilmington and NW of Philly had the highest total reported in Accuweather summary.

Posted by: JerryFloyd1 | February 11, 2010 2:52 PM | Report abuse

Great article, and very informative chart. No wonder I felt so cold while I was shoveling during the blizzard Wednesday morning.

Posted by: InVA1 | February 11, 2010 3:06 PM | Report abuse

AndrewRockville, according to NWS:
"The air temperature has to be BELOW freezing in order for frostbite to develop on exposed skin. Wind chill can bring the temperature to below freezing for humans and animals."

In addition to the dangers of wind chill, those conditions could also cause hypothermia (a lowering of the core body temperature) if you're out in them for too long.

Posted by: Ann-CapitalWeatherGang | February 11, 2010 3:23 PM | Report abuse

krosseel - Cold weather injuries and illnesses are obviously a huge concern in Antarctica. I was there during the Southern Hemisphere summer, and the coldest temperature I experienced was -25C at the South Pole. When combined with wind, this felt much colder. I traveled with the U.S. Antarctic Program, which does a great job training participants in outdoor preparedness and providing necessary clothing. Also, with the exception of being on the coast, the wind there feels much different because the air is so dry. In D.C. yesterday, the air was also damp, which makes the effect of wind chill feel worse.

I posted a few articles during my trip. There will be more coming after this wintry weather dies down a bit. Thanks for your interest.

Posted by: Ann-CapitalWeatherGang | February 11, 2010 3:34 PM | Report abuse

AndrewRockville: According to the NWS's "Office of Climate, Water, and Weather Services," the "air temperature has to be BELOW freezing in order for frostbite to develop on exposed skin. Wind chill can bring the temperature to below freezing for humans and animals."

However, I admit that this answer is ambiguous since the first sentence seems to contradict the second. Therefore, I spoke with a NWS representative who, on condition of anonymity, said that that answer was wrong--that the air temp does NOT need to be below freezing for frostbite to set in, since frostbite, in a literal sense, does NOT necessarily mean a freezing of the cells but rather a multi-stage process which starts with constriction of cells and progresses onward with further damage. Whether this ultimately results in as much bodily harm as if the ambient air temp is below freezing is an open question.

Don Lipman-Capital Weather Gang

Posted by: Weatherguy | February 11, 2010 3:50 PM | Report abuse

AndrewRockville: We realize that you've now received somewhat different responses from Ann Posegate and me on the same question. Now you can realize that this issue is not quite as simple as it seems.

You, Ann, and I all quoted the NWS response, which would have been the last word had it not been for the second sentence of their explanation, "Wind chill can bring the temperature to below freezing for humans and animals."

As I said, the ambiguity of that statement caused me to ask the NWS media rep about it, who admitted that the explanation was contradictory and unsatisfactory--that the frostbite process can start with the ambient air temp above freezing. How rapidly it will progress and severe it can become, of course, depends on actual air temp, wind speed, and exposure. If there are any M.D's reading these comments, we would appreciate your take on this.

Don Lipman-Capital Weather Gang

Posted by: Weatherguy | February 11, 2010 4:45 PM | Report abuse


Generally speaking, heat loss is proportional to the difference in temperature. Your body is roughly a constant temperature, so heat loss would normally just be a function of outside temperature.

Wind enhances heat loss - its why we seek it out on hot days, and the enhanced heat loss is what the "wind chill" is supposed to represent.

Inanimate objects, at ambient temperature, aren't gong to have any heat loss, wind or wind.

Posted by: jace2 | February 11, 2010 7:58 PM | Report abuse

wind or NO wind, that should have said.

Frostbite involves freezing of body tissue, so the temperature of your fingertip, say, has to drop below 32. That normally won't be possible if the air temperature is above 32, regardless of wind - but I think that if you add in some evaporational cooling, maybe from a wet glove, you might be able to tip the scales.

Posted by: jace2 | February 11, 2010 8:02 PM | Report abuse

Why are wind chill factors only used in the winter? Seems like a breeze on a 95 degree day would also have a cooling effect, but that's never reported anywhere...

Posted by: spgass1 | February 11, 2010 10:24 PM | Report abuse

First, I want to thank CWG for all their hard work during the mess that Jon Stewart called "unusually large snowstorm." You were very informative and entertaining. I felt like I was in contact with people instead of being stuck HOME all week!!!

I have a mildly amusing story about wind chill. It was 1993, and hubby & I had just moved to Savannah. In March 1993, there was a 'storm of the century' which dumped a ton of snow & ice on my parents north of Baltimore. In south Georgia, there were snow flurries, or so I've been told, and everything (including the mall) shut down. I know this because we lost power and wanted to go somewhere warm and lighted. And we had to eat. We had an electric stove & the grill was still in storage.

Well, the radio DJs were telling people to stay off the overpasses and bridges -- and there are a lot of bridges in that region -- because THE WIND CHILL FACTOR would make the overpasses freeze faster! Yes, they said wind chill, and they said it repeatedly! Now I know that bridges & overpasses DO freeze faster, because there is no soil beneath to insulate them and help them retain heat. True phenomenon, wrong terminology, but it still made me NUTS!

And that was when I learned that people, no matter how far south or north they are, really do not care how they do things where "y'all" are from.

Posted by: ed_mom | February 12, 2010 5:13 PM | Report abuse

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