# Odd Fog Question **URL:** \ **Category:** Factual Questions\ **Created:** [February 6, 2003, 4:36am UTC](https://boards.straightdope.com/t/odd-fog-question/153131 "2003-02-06T04:36:54Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 6, 2003, 4:36am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/1 "2003-02-06T04:36:54Z")
This is my first actual question on this board, so I hope I am following the correct protocol. šŸ™‚ The question is this. I live in Toronto and drive into work every day on the lakeshore route, which has a good view of lake Ontario. This winter has been very, very cold, with many days below -20 C or even colder. On some clear, still mornings, when it is very cold, I have noticed that the lake is literally covered with what looks like plumes of steam or fog rising from the water - sometimes, right out to the horizon. To me, this looks very odd indeed, as I associate steam with hot, not cold, water. I am sure this has a logical explaination that any meteorologist would know right away - can anyone explain this cold-weather steam? šŸ˜• ---
**Author:** ![Reeder](https://avatars.discourse-cdn.com/v4/letter/r/c6cbf5/32.png) [@Reeder](https://boards.straightdope.com/u/Reeder)\ **Post date:** [February 6, 2003, 4:39am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/2 "2003-02-06T04:39:57Z")
The water is indeed warmer than the air. Which is what causes the water vapor. As for the dynamics someone will be along soon and explain them Iā€™m sure. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 6, 2003, 4:41am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/3 "2003-02-06T04:41:32Z")
Bodies of water hold heat much better than the air does. On a chilly morning, the air may have gotten quite cold overnight, but the water will still retain much of the warmth from the previous day, and so can be several degrees warmer than the air over it. Water vapor evaporating from the surface will condense quickly in the cold air, forming a fog over the lake. ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 6, 2003, 4:46am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/4 "2003-02-06T04:46:40Z")
Naturally the water must be warmer than the air - there is no ice, so it must be warmer than 0 degrees C. Is steam then a function of the extreme difference in temperature between the water and the air - rather than, as I had previously thought, a function of boiling/really hot water? If so, how much temperature difference is required to produce steam? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 6, 2003, 4:54am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/5 "2003-02-06T04:54:23Z")
The misconception here is that you can see steam. You canā€™t. Steam is water vapor at the local boiling point of water or higher (212 F or 100 C at sea level). You canā€™t see water vapor until it drops below that temperature and begins to condense into tiny droplets suspended in the air. What you are seeing over the lake is not steam (which is a **gas** ), but microscopic droplets of **liquid** water in the air. Hope this clears things up. ---
**Author:** ![kniz](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@kniz](https://boards.straightdope.com/u/kniz)\ **Post date:** [February 6, 2003, 5:17am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/6 "2003-02-06T05:17:30Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > **Bodies of water hold heat much better than the air does.** Actually water does not change temperature as fast as air does. In warmer climates the water will be cooler than the air. Land also changes temperature faster than water, thus causing winds in the morning and evening near the shore. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 6, 2003, 5:20am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/7 "2003-02-06T05:20:39Z")
Heat and temperature are **not** the same thing. I stand by my original statement. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 6, 2003, 8:08am UTC](https://boards.straightdope.com/t/odd-fog-question/153131/8 "2003-02-06T08:08:54Z")
I think knizā€™s point is that, not only do bodies of water hold heat better than air, bodies of water are also harder to heat than air. The effect is reversed, in other words. ---
**Author:** ![ratatoskK](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ratatoskk/32/2987_2.png) [@ratatoskK](https://boards.straightdope.com/u/ratatoskK)\ **Post date:** [February 6, 2003, 12:12pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/9 "2003-02-06T12:12:52Z")
I have been told that here in New England, fog like that coming off the ocean is called ā€œarctic sea smoke.ā€ (Donā€™t know if that is reliable info.) ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 6, 2003, 3:59pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/10 "2003-02-06T15:59:08Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*The misconception here is that you can see steam. You canā€™t. Steam is water vapor at the local boiling point of water or higher (212 F or 100 C at sea level). You canā€™t see water vapor until it drops below that temperature and begins to condense into tiny droplets suspended in the air. What you are seeing over the lake is not steam (which is a **gas** ), but microscopic droplets of **liquid** water in the air. Hope this clears things up. \*\* Whether the stuff coming off the surface be steam or fog, or some yet third definition, I have yet to hear a reason why it forms over the lake when the air is really, really cold. šŸ˜• I must say, the _effect_ is really striking. Is there a weather person in the house who can explain why it happens? ---
**Author:** ![tanstaafl](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tanstaafl](https://boards.straightdope.com/u/tanstaafl)\ **Post date:** [February 6, 2003, 4:06pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/11 "2003-02-06T16:06:27Z")
> [@](#): > > Whether the stuff coming off the surface be steam or fog, or some yet third definition, I have yet to hear a reason why it forms over the lake when the air is really, really cold. OK, step by stepā€¦ 1. The water in the lake is warmer than the air. 2. Water evaporates from the lake. 3. A few inches above the lake the air is colder so the vapor which just evaporated condenses back into water droplets. This is the fog you are seeing. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 6, 2003, 4:09pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/12 "2003-02-06T16:09:03Z")
Isnā€™t that what I said to begin with? šŸ˜ƒ ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 6, 2003, 4:21pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/13 "2003-02-06T16:21:41Z")
> [@](#): > > \*Originally posted by tanstaafl \* > \*\*OK, step by stepā€¦ > > 1. The water in the lake is warmer than the air. > > 2. Water evaporates from the lake. > > 3. A few inches above the lake the air is colder so the vapor which just evaporated condenses back into water droplets. This is the fog you are seeing. \*\* Okay, maybe I am just having a hard time loosing my ā€œcommon senseā€ or rather mistaken opinion that evaporation is caused by high heat, rather than temperature difference ā€¦ I now understand that it is the _temperature difference_ between the water, which is relatively warmer, which causes the evaporation. You see, not being a scientist, I associate steam or fog with the stuff that comes off of a hot cup of tea ā€¦ I see now that the answer is, that as far as the water in the lake is concerned it is as much ā€œhotterā€ than the air as the water in the teacup is. So my next question is - how much difference must this be, in order for evaporation to form visible fog? When I look out my car window, can I tell approximately what temperature the air is by observing how foggy the lake is (assuming that the water temp is just above zero C and there is no wind?). I realize that the more fog, the colder, but at what temperature does this phenominon begin to occur? ---
**Author:** ![critter42](https://avatars.discourse-cdn.com/v4/letter/c/7ba0ec/32.png) [@critter42](https://boards.straightdope.com/u/critter42)\ **Post date:** [February 6, 2003, 5:28pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/14 "2003-02-06T17:28:39Z")
Hereā€™s the answer to the OP: [USA Today](http://www.usatoday.com/weather/wsfog.htm) (yes, **Q.E.D.** , I know itā€™s the same thing you said, but itā€™s got REALLY PRETTY PICTURES šŸ˜‰ ) At the bottom of [this](http://www.usatoday.com/weather/wcloud0.htm) page is links to descriptions of the different kinds of fog that can form. critter42 ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 6, 2003, 7:03pm UTC](https://boards.straightdope.com/t/odd-fog-question/153131/15 "2003-02-06T19:03:23Z")
> [@](#): > > \*Originally posted by critter42 \* > \*\*Hereā€™s the answer to the OP: > > [USA Today](http://www.usatoday.com/weather/wsfog.htm) > (yes, **Q.E.D.** , I know itā€™s the same thing you said, but itā€™s got REALLY PRETTY PICTURES šŸ˜‰ ) > > At the bottom of [this](http://www.usatoday.com/weather/wcloud0.htm) page is links to descriptions of the different kinds of fog that can form. > > critter42 \*\* Thanks critter42 - that is just about my level. šŸ˜‰ I know know that what I saw is called ā€œsteam fogā€. Makes sense!