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