Wind chills won't freeze water

If the ambient temperature is 35° F with a wind chill factor of 25° F, will water freeze? I say no, my friend says yes. How can we test this during this time of the year?  Mike and Keith, Benton, Tennessee

Rochester, Minnesota blizzard in March 1966.  Photo courtesy of the NOAA.

You’re right. A wind-chill factor of 25° F (- 4° C) will not freeze water if the air temperature is 35° F (2° C).  Water changes state according to the temperature of the body of the water.  In this case, the water and air temperature are about the same — too high to freeze water.

How to test this during the summer? Tough. Your best bet is to rig up a refrigerator with a 15 mph fan. It takes a 15 mph (24 kph) wind to produce a wind chill factor of 25° F if the air temperature is 35° F. (Related: detailed instructions for carrying out the experiment.)

Further Surfing:

NOAA: National Weather Service wind chill chart

Safety Central: $20-battery operated fan

(Answered June 27, 2003; updated Oct. 3, 2007)

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Readers' Comments

• I was wondering - lets say the temp is 28 F and there is a 30MPH breeze blowing across the entire surface of water. Would the breeze prevent the water from freezing because of the constant movement on the surface of the water?  Tornado Fan, Mobile, Alabama
   

Reply:  Interesting thought, but the breeze would actually make the water freeze faster. Ice forms in ponds and lakes from the edge or shore (where it's most shallow) outwards towards the center.

As long as some the center remains liquid, some water will evaporate from the lake into the air. We've all seen 'steam' rise from a lake into cold air. The water vapor is warmer than the water and warmer still than the cold air above the lake. So, the water vapor, mixed with air, forms an insulating layer that slows freezing of a lake.

The lake will eventually freeze even in calm conditions, because convective currents form in the lake and above the water. But a nice stiff breeze will blow that insulating layer away from the water's surface and hasten the freezing process. The water will freeze faster. 
 

• I did an experiment a few years ago on just what you asked...pan of water 33-35f temp and a fan...the water didn't freeze at all...even after the temp dropped below 32 it didn't seem to freeze any faster than the control pan of water we had set up...so this myth is busted...lol  Auburn, Opelika, Alabama
   
• A surprisingly complicated topic - and nobody has mentioned two more factors: 
  1.  Lakes won't freeze until all the water is 4 degrees Celsius, where water has maximum density.  Until then the 4-degree water sinks and is replaced by warmer, lighter water from below.  It's why ice forms at the surface instead of the bottom of the lake.
  2.  An open thermos of water outside on a 33-degree (F.) cloudless night will probably freeze from a net loss of heat, even though the ambient air is above freezing. Jim, Titusville, New Jersey
   
• Wind chill is a basic factor. Its not really how one "feels". But how much the body can produce heat to keep itself warm before the wind blows our internal heat off of ourselves. I'm not if that makes any sense. So ones body will freeze faster when the wind chill is 10 instead of 40. That's why I hate the expression, "how it feels". So ya I see no reason why it wouldn't freeze in that case.  Yet on the other hand water freezes because of less molecular movement. Would the wind cause less?  Spetrm, Jacksonville, Florida
   
• I wouldn't be ready to bet the farm either way on this one yet. Where I work we are situated on the top of a hill with an almost constant wind. Even in the blazing sun the water temperature is significantly lower than the ambient temperature in the above ground pool we have for the kids. Fellow with a lot more physics background explained that breeze over the top was increasing rate of evaporation which drops temperature and airflow over the sides decreasing amount of positive heat transfer from air to container. I know matter gets "squirly" at transition points and water more-so than most: Only compound which expands when it solidifies if I remember correctly so that may have some factors I'm missing. I have to give credit to A's experiment and I'm way out f my field but none of my profs would have let me get away with a 1.n set, For now I'm with Spetrm. Why would water sitting in a solid container behave any differently than water in a bladder propped up internally with a bunch of sticks (thats you and me) given the same exposed surface area? I'm gonna have to get back to you on this.  ShenValleyFlyFish, Greenwood, Virginia
   
• OK I'm convinced. I found more than one source. Will make it freeze faster after but ambient must be below freezing. The water in the bladder wouldn't freeze before that either. Wind chill is rate of heat transfer comparison not an actual temperature. Every thing freezes at 32F DUH its just how long it takes to overcome internal heat generation. Ok now I get it. Thanks for making me think and learn. I miss school.  ShenValleyFlyFish, Greenwood, Virginia
   
• Does wind chill have an effect on inanimate objects? For example will the wind chill have an effect on concrete setting up? Sam, Columbus, Ohio

Reply:  Wind chill doesn't affect inanimate objects, Sam, in the same way as animate.  Wind chill blows away the thin layer of air next to our skin that we've warmed with our body heat.  That makes us feel cold.  But, wind chill rarely has a similar effect on an inanimate object, which can't, in general, warm the thin layer close to its surface.  However, wind could effect the setting up of concrete, because wind fosters evaporation.  In fact, we generally put wet sacks over concrete so the concrete doesn't dry out as it sets up. 

• Let us not forget that concrete produces heat during the chemical reaction of curing. The concrete like brick mortar sets up faster in warmer weather. It also freezes when it gets cold enough. This is where wind chill comes into effect. Notice I said when it gets cold enough not when it gets below 32F. That's because it has it's own heat from the chemical reaction. The exact freeze temp would depend on temperature, wind chill and amount of mortar or concrete. The more concrete or mortar, the more heat.  Mike, Mchenry, Illinois
   
• Wind Chill has nothing to do with the temperature of an object in the open. It relates to the rate at which the objects temperature will drop until it reaches ambient temperature. If the Air temperature is Zero [0] DegF and the wind speed is 30 MPH, the cooling effect would be as if the object was in -26 DegF with no wind. Once the object reached 0 DegF it would get no colder.   Siva06, Cleveland, Ohio
   
• I'm still confused over wind-chill impacting inanimate objects (let's forget about concrete but what about my car?) I live in the far north, and opinions are split on whether wind-chill will impact your car (and it's block heater) or not, and if so, how does it impact it? Kim, Regina, Saskatchewan, Canada

  Reply: In the wind, your car (parked outside) will cool down faster, after you turn the engine off.  Wind blows away the warmer air (warmed by the warm car) next to the surface of the car.  This increases the temperature difference between air and car.  The car, therefore, cools faster.  
  
  But the car will arrive at the ambient outside temperature, not a lower value.  For example, if the temperature outside is -20 degrees F (-29 C) and the wind is blowing 30 mph (48 km/h), your car will cool to -20F faster than in calm conditions, but it will just cool to -20F — the same temperature as the air around it. 
  
  By the way, -20 F and 30 mph corresponds to a wind chill temperature of -53 F (-47 C).
  
  The block heater complicates the picture, but basically it's the same deal. The wind blows under the car, hits the engine and cools the engine block, too.  So, the engine block heater may not be able to keep the the engine, coolant and oil as warm as under calm conditions. In fact, if conditions are bad enough, you might have trouble starting the car.
   

• The car will cool to only the ambient temperature, but water will be cooled according to its wet bulb temperature, the wind speed, and the relative humidity or humidity ratio.  Look at a psychometric chart.  If for example, the relative humidity is 20%, and the ambient temperature is 7 degrees Celsius, then water can be cooled to slightly below 0 degrees Celsius by "wind chill".  Thus, if you insulate a container of water from the ground as best as possible, it will freeze if sufficient wind is blown over it at about 5 or 6 degrees Celsius ambient temperature.
  
  Wet bulb temperatures are (or were) determined by taking two thermometers and putting a wet sock over one and swinging them through the air, the one with the wet sock on it will be significantly cooler. Thus "wind chill" has a much greater effect on things which are wet or contain water that can evaporate.  This is due to the latent heat of evaporation of water.  Somebody, World

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