# Lake surface temperatures - why so inaccurate? **URL:** \ **Category:** Factual Questions\ **Created:** [September 7, 2012, 3:31pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999 "2012-09-07T15:31:28Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 7, 2012, 3:31pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/1 "2012-09-07T15:31:28Z")
I have tried to determine from my home the likelihood that I’ll be able to take a swim in Lake Michigan, based on the water temp. One way I’ve tried is to consult a site that reports surface temperatures ([CoastWatch Great Lakes SST Contour Map](http://www.coastwatch.msu.edu/michigan/m5.html)). I don’t know the exact method used, but since I was in the water yesterday and the water was quite warm - maybe upper 70’s - I can’t figure out why today’s map shows among other things that the temperature of the water between Chicago and Waukegan, for instance, is about 33 degrees. In fact a lot of the temperatures reported are way cooler than reality suggests. This renders the map useless unless I can figure a way to interpret it. Is there some way to understand such numbers so that I can judge the actual water temp? ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [September 7, 2012, 3:47pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/2 "2012-09-07T15:47:25Z")
If you click the “Help Pages” link towards the bottom of that page you will find the answer to your question. > [@](#): > > 1. Cloud covered areas of the lake surface cannot be read accurately by NOAA satellites so the computer program colors them black. Areas near the black masked cloud cover may not be as precisely reported as those some distance from the clouds. CoastWatch images are generally representative of surface temperature conditions, they are not as accurate as your road atlas. So the numbers in the black areas are most likely bad and even in the grey area they may be suspect. ---
**Author:** ![Mr\_Downtown](https://avatars.discourse-cdn.com/v4/letter/m/8e8cbc/32.png) [@Mr\_Downtown](https://boards.straightdope.com/u/Mr_Downtown)\ **Post date:** [September 8, 2012, 12:57am UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/3 "2012-09-08T00:57:34Z")
Also worth knowing that when the wind comes from the east or north, it blows chilly water from the center of the lake to the shore. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 8, 2012, 1:03am UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/4 "2012-09-08T01:03:06Z")
There’s a wide variability of Lake Michigan temperatures depending on depth, location, surface conditions, and did I mention location? There are two central-lake bouys, one near Chicago and one in the north part of the lake. Both are about 50 miles from shore, so would hardly do for swimming temps unless you plan to dive off of one of them; the shore temps can be quite different. And the temp can change drastically – 20F degrees – overnight under some conditions. Generally, late summer is best for swimming on the first day of a storm. The water is warm, the waves, big – fun for kids. But the second day, the cold water takes over and 70F can become 50F with no visual confirmation. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 8, 2012, 1:13am UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/5 "2012-09-08T01:13:12Z")
Although it won’t help you much for shore swimming conditions, here are the links to the 2 Lake Michigan buoys that report weather conditions hourly thru the Internet (3 seasons only): [North Lake Michigan](http://www.ndbc.noaa.gov/station_page.php?station=45007) [South Lake Michigan](http://www.ndbc.noaa.gov/station_page.php?station=45002) ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 8, 2012, 1:57pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/6 "2012-09-08T13:57:47Z")
> [@Baracus](#): > > If you click the “Help Pages” link towards the bottom of that page you will find the answer to your question. So the numbers in the black areas are most likely bad and even in the grey area they may be suspect. Thanks. I saw something about that and for some reason totally ignored it. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [September 8, 2012, 7:24pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/7 "2012-09-08T19:24:05Z")
I live on Lake Michigan also and find this site to be far more accurate: [http://tidesandcurrents.noaa.gov/ofs/lmofs/now\_temp.shtml](http://tidesandcurrents.noaa.gov/ofs/lmofs/now_temp.shtml) ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 8, 2012, 7:48pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/8 "2012-09-08T19:48:52Z")
Thanks, Doc. I’ll see how accurate that is the next time I get in the water - most likely several days from now. (Although the info does seem to be a bit off, i.e. indications that the south end of the lake was in the 80’s yesterday at around 3 p.m. I doubt that.) ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [September 8, 2012, 10:28pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/9 "2012-09-08T22:28:09Z")
I’ve also noted over the decades that right along the shore, the water conditions can vary wildly. I’ve experienced 15 degree or more differences between 5 feet off shore and 50 feet off shore. I’ve experienced that same degree of difference from the first 6 inches of water depth to down about 3 or 4 feet. It’s good to remember that most of Lake Michigan’s water is always right about 40 degrees or so, no matter what time of year. It’s only that thin skin on top that warms up much. And that surface water can change real quick, and really, really locally. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 8, 2012, 10:31pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/10 "2012-09-08T22:31:41Z")
> [@Qadgop\_the\_Mercotan](#): > > I’ve also noted over the decades that right along the shore, the water conditions can vary wildly. I’ve experienced 15 degree or more differences between 5 feet off shore and 50 feet off shore. I’ve experienced that same degree of difference from the first 6 inches of water depth to down about 3 or 4 feet. Which is why those maps don’t help much if you want to step in the water from shore; not enough detail. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 8, 2012, 10:59pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/11 "2012-09-08T22:59:26Z")
Yeah - I just want a lazy man’s way of dipping my feet in the water without having to walk over there, discover it’s too cold today, and have to walk back. It’s only a block, mind you, but I’m really a slug. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [September 10, 2012, 11:20am UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/12 "2012-09-10T11:20:31Z")
> [@CC](#): > > I have tried to determine from my home the likelihood that I’ll be able to take a swim in Lake Michigan, based on the water temp. One way I’ve tried is to consult a site that reports surface temperatures ([http://www.coastwatch.msu.edu/michigan/m5.html](http://www.coastwatch.msu.edu/michigan/m5.html)). I don’t know the exact method used, but since I was in the water yesterday and the water was quite warm - maybe upper 70’s - I can’t figure out why today’s map shows among other things that the temperature of the water between Chicago and Waukegan, for instance, is about 33 degrees. In fact a lot of the temperatures reported are way cooler than reality suggests. This renders the map useless unless I can figure a way to interpret it. Is there some way to understand such numbers so that I can judge the actual water temp? Right now it is showing temperatures of about 71-72F across most of the lake. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [September 10, 2012, 1:21pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/13 "2012-09-10T13:21:29Z")
> [@CC](#): > > Yeah - I just want a lazy man’s way of dipping my feet in the water without having to walk over there, discover it’s too cold today, and have to walk back. It’s only a block, mind you, but I’m really a slug. If it’s a really short block, [QUOTE= [ColeParmer.com](http://ColeParmer.com)] Most IR thermometers have a maximum measuring distance of approximately 100 feet (30 meters), depending on atmospheric conditions. [/QUOTE] Hope that helps..🙂 ---
**Author:** ![Mr\_Downtown](https://avatars.discourse-cdn.com/v4/letter/m/8e8cbc/32.png) [@Mr\_Downtown](https://boards.straightdope.com/u/Mr_Downtown)\ **Post date:** [September 10, 2012, 3:30pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/14 "2012-09-10T15:30:50Z")
Is [this NOAA site](http://forecast.weather.gov/product.php?site=LOT&product=OMR&issuedby=LOT) more helpful? ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [September 10, 2012, 7:32pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/15 "2012-09-10T19:32:08Z")
location can have drastic effects. on the Michigan side on calm sunny days you might have temperatures off the beach be in the upper 70 degrees. when you have a west wind the temperatures off the beach be in the 50 degrees. on the Wisconsin side near shore water that has warmed might get blown out when it’s windy. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 10, 2012, 8:39pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/16 "2012-09-10T20:39:32Z")
It’s windy today and the water at shore is 73F; I measured it. It may be your last chance for the season. Come on in! ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [September 11, 2012, 5:27pm UTC](https://boards.straightdope.com/t/lake-surface-temperatures-why-so-inaccurate/633999/17 "2012-09-11T17:27:47Z")
> [@Musicat](#): > > It’s windy today and the water at shore is 73F; I measured it. It may be your last chance for the season. Come on in! 6:30 PM last night, the online map I linked to earlier reported water temps between 72-75 by me. I measured the temp myself at 72. Nice and rough, too! 😃