June 20, 2021

Humid Air Makes Ice Cream Cones Melt Fast!

Recently, I was walking along the south shore of Long Island with another meteorologist, Nick Weber, and we decided to purchase some ice cream cones.

Nothing fancy...  a sugar cone with two scoops.   The market was air-conditioned and the ice cream was fine as we paid for it.  

But nearly the second we went outside, the ice cream started to melt very, very rapidly.

I had never seen anything like it. And you can imagine our desperation to enjoy our treats before they disappeared.  

The temperature outside was not excessive....roughly 75F, with a light wind, roughly 5 mph by my estimate.


Within a minute or two, our hands were sticky with melted ice cream and we asked ourselves what was going on.  And we both thought of the answer at the same time:  the humidity, and particularly the high dew point.

Remember dew point is the temperature at which condensations (100% relative humidity) occurs when air is cooled.

If air has a lot of water vapor and the dew point is high, water vapor in the air can condense on cold surfaces,  like ice cream.  And when water vapor condenses, it releases a large amount of energy:  the latent heat of condensation, which is around 600 calories per gram of water condensed.  As most of you know, calories are a unit of energy.  

Such condensation is like putting a strong heater on the surface of the ice cream.

How much energy does it take to melt ice cream?  Well, since ice cream is mostly water, let's use the number for water, the heat of fusion, which is about 80 calories per gram of ice melted.

So this is interesting.   Every gram of water vapor in the air that condenses can melt 7-8 grams of ice or ice cream.     So condensation of water vapor might be very effective in melting ice cream!

But what about our situation?  Was the air humid enough to undermine our enjoyment of our cones?

We were on Fire Island at the time and the nearest observing site was Bay Shore, Long Island, where the dew point was 73F (see map, marker is where we were).   That is a high dew point;  if you cooled the air to that temperature, water would condense.  Seattle almost never gets dew points that high; our typically summer days have dew points in the lower to mid 50s.

Location of the ice cream melt down (red marker) and nearby observations

So the air had a lot of moisture in it and the ice cream was plenty cold  enough to cool the air to the dew point, so massive condensation and warming were going on.  Plus, the ice cream was packed by hand, and thus had a LOT of surface area, which helped the melting along.  And, of course, there was melting due to warmth of the surrounding air.

It was obvious the air was laden with water vapor, because the sky was very hazy...almost fog-like.

So I think we solved the mystery!  Huge heating of the ice cream as water condensed on its surface.

In the Northwest, such melting of ice cream is less of a problem, because our air ...particularly in summer...  is relatively dry (low dew points) because ironically our air has passed over cool water.  The amount of water vapor air can "hold" is related to temperature and our cool coastal waters (only around 50F) can not inject a lot of water vapor into our air.

So we can take our time eating our favorite ice cream confection because of the cool Pacific.

Ironically, the cool Pacific Ocean allows us to enjoy our ice cream longer.

And the effects of moisture on warming things that we consume doesn't stop with ice cream! 

 When enjoying a cold beverage, particularly full of ice, you can see the condensation on the outside of the glass or can (see below).

Condensation is occurring and powerfully warming your beverage.


To stop the condensation of water is the main benefit of drink koozies...those rubber-like enclosures for cans (see below)

It is good to be back in the Northwest, where I can take my time eating my ice cream or enjoying a cool drinkl

16 comments:

  1. Had the same happen in Florida this year. Dew point in the upper 70s and 10mph breeze - the ice cream just fell apart in a minute.

    ReplyDelete
  2. Hi Cliff,
    I opened your blog a few minutes ago and noticed an ad by lunatic fringe Tom Fitton's Judicial Watch Website. I have been opening your blog every minute or so and I notice the ads continually change. Do you have control over who advertises on your blog?

    ReplyDelete
    Replies
    1. Gary... I do not select the ads. Adsense selected them based on your interests and leanings. It should be selecting the topics and sites you typically go to...cliff

      Delete
    2. Lunatic fringe? you mean the libs. So Tom would not be in that group. And don't drag your insanity into a weather site.

      Delete
  3. I live in Anacortes where the sea breeze generally keeps us cool. But I have noticed inside my house at a perfect 71 degrees but 50% humidity I start to get sticky!

    ReplyDelete
  4. Great inspiration for an instant impromptu blog, Cliff!

    ReplyDelete
  5. 90 degrees next saturday? we'll see...

    ReplyDelete
  6. Fun piece - dew point has real meaning weather-wise but the concept isn't broadly understood. (By the way, love the can cozy!)

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  7. Great blog..cliff
    As I am your sister I personally have had similar ice cream experiences on Long Island..You will have to come back for more!🍦

    ReplyDelete
    Replies
    1. Indeed! I used to live in Old Lyme. I still miss the "active" weather of the East- and saltwater that you can actually swim in. And I had lots of ice cream on hot summer afternoons.

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  8. Another example of the effects of the latent heat of condensation: Some of you will have had the unfortunate experience of having burned your fingers on the steam jet from a boiling kettle. You may have noticed that it burns a lot faster than the air jet from a hair dryer, though the latter is probably at least as hot as steam from a kettle..

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  9. I remember reading somewhere that a hit baseball would travel the furthest in hot, humid air and not in hot, dry air. I guess it has something to do with the water molecules offering up less resistance to the ball than air molecules. All I know is that hot and humid conditions definitely do cause people to travel quickly, and it's usually in the direction of somewhere cooler

    ReplyDelete
    Replies
    1. Hot, humid air is less dense than hot, dry air. Since air density is part of the formula for drag (D = Cd * rho * 0.5 * v^2) the drag will be proportional to density. Lower density air, ball goes farther.

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  10. DILLIGAF.
    Classic, I bet only a hadful of folks here know what that means.
    Thanks for sharing the ice cream sory!

    ReplyDelete
  11. I live in New England(*) where people sometimes refer to "fog eating snow." I.e., fog melts snow quickly.

    Several years ago I decided that had cause and effect reversed, and that what really happens is that air with a dewpoint above freezing comes into contact with snow. Water quickly condenses on the snow, releasing the latent heat in the water vapor. Of course, it goes into melting the snow, not heating the air.

    In fact, the snow cools the air, so on top of the water condensing on the snow directly, water vapor condenses in mid air as fog.

    Snow and ice cream in air with a 73°F dew point has no chance of lasting long!

    *: My brother lives in Bend OR. He organized a family reunion. I'm flying out Monday. June 28th. Forecast high 104°F. Ah well, if the weather has to be bad, at least it may be record setting weather.


    ReplyDelete
  12. Well what i've noticed with our major snow events (even if its not muggy like east coast, obviously), is that our snow tends to melt faster even with lower temperatures and no rain. This is because its so damp and wet outside. When I was in Illinois a couple years ago, they had a major snow event before I got there in December. They had multiple warm, sunny days into the mid 60s! But the snow did not melt as fast and even though the sun was shining I think it was just too dry.

    ReplyDelete

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