<p>The value -999 is likely the "fill value" used in the dataset when data is missing or is not being properly filtered or handled when displayed.  In the specific case on the website you cite, it is likely a problem with the algorithm for wind chill (the "feels like" temperature this time of year). </p>

<p>It isn't a physical value and only means the value is missing. Furthermore, -999°C is not a possible value because <a href="https://en.wikipedia.org/wiki/Absolute_zero">absolute zero</a> is –273.15°C, and it's not possible to be colder than this (at least <a href="http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146">not in any meaningful way</a>, and certainly not because of wind chill). The <a href="https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on_Earth">coldest recorded temperature</a> on earth is around –90°C. </p>

CC BY-SA 3.0
2017-03-04T05:14:15.827Z
No, it isn't stupid. For analytical purposes spreadsheets necessarily have a numerical field, so we have to insert a 'stupid' number that we can recognize as spurious, and filter out when it comes to statistical analysis.
Gordon Stanger
CC BY-SA 3.0
2014-12-16T00:07:46.537Z
Personally, I prefer -9e99 (or 9e99) as a dubious (and obvious) fill value. But yes, this is almost certainly what this is.
David Hammen
CC BY-SA 3.0
2014-12-16T05:33:40.937Z
NASA often uses -9999... just to be sure they put the extra 9
f.thorpe
CC BY-SA 3.0
2014-12-16T19:43:01.133Z
the data on that page comes from weather underground, see http://www.wunderground.com/weather/api/d/docs?d=resources/phrase-glossary 'values will = -9999 or -999 for Null or Non applicable (NA) variables' I also suspect that 'feels like' is the heat index value, not the wind chill, which is why it's undefined ( you're not going to get heat stroke there at the moment )
Pete Kirkham
CC BY-SA 3.0
2014-12-16T19:45:47.087Z
@PeteKirkham "feels like" is typically heat index in the warm season and wind chill in the cold season.  Some provides use additional factors in their algorithm as well.
casey
CC BY-SA 3.0
2015-01-12T03:28:33.027Z
Stupid languages that don't have an `NA` numeric value >:/
naught101
CC BY-SA 3.0
2014-12-15T20:55:27.480Z
2014-12-15T21:12:50.247Z
2014-12-15T21:12:50.247Z
casey
<p>I was checking the weather forecast just now, and it is showing that it "feels like -999 °C". I never heard or saw -999 °C before. I searched other weather channels, and they were showing that it feels like 2 °C. What is the meaning of -999 °C, irrespective of the weather?</p>

CC BY-SA 3.0
2014-12-16T00:24:48.870Z
That means its cold.  Really really cold.  So cold that they really don't know how cold it actually feels.  OR it just means that a programmer screwed up.
ChrisLively
CC BY-SA 3.0
2014-12-16T02:37:27.123Z
@ChrisLively Or there was missing data in one of the input fields to their "feels like" algorithm. It probably isnt a straight wind chill and may depend on more than just temp and wind.
casey
CC BY-SA 3.0
2014-12-16T14:25:56.737Z
[Oh, the weather outside is frightful.](http://thedailywtf.com/articles/Oh-The-Weather-Outside-is-Frightful)
user
CC BY-SA 3.0
2014-12-16T16:07:20.753Z
@casey: a programmer is still supposed to take those types of things into account...
ChrisLively
CC BY-SA 3.0
2014-12-18T18:01:27.390Z
This really sounds like a mistake to me!
L.B.
<meteorology><weather-forecasting>
What is the meaning of -999 degrees Celsius?
eLg
# What is the meaning of -999 degrees Celsius?

(Asked by: username_0 on 2014-12-15)

I was checking the weather forecast just now, and it is showing that it "feels like -999 °C". I never heard or saw -999 °C before. I searched other weather channels, and they were showing that it feels like 2 °C. What is the meaning of -999 °C, irrespective of the weather?

**Tags:** meteorology, weather-forecasting

> **Comments:**
> **username_1**: That means its cold.  Really really cold.  So cold that they really don't know how cold it actually feels.  OR it just means that a programmer screwed up.  
> **username_2**: @username_1 Or there was missing data in one of the input fields to their "feels like" algorithm. It probably isnt a straight wind chill and may depend on more than just temp and wind.  
> **username_3**: [Oh, the weather outside is frightful.](http://thedailywtf.com/articles/Oh-The-Weather-Outside-is-Frightful)  
> **username_1**: @username_2: a programmer is still supposed to take those types of things into account...  
> **username_4**: This really sounds like a mistake to me!  

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## 1 answers

### Answer by username_2 on 2014-12-15. Score: 42 | Accepted answer

The value -999 is likely the "fill value" used in the dataset when data is missing or is not being properly filtered or handled when displayed. In the specific case on the website you cite, it is likely a problem with the algorithm for wind chill (the "feels like" temperature this time of year).

It isn't a physical value and only means the value is missing. Furthermore, -999°C is not a possible value because [absolute zero](https://en.wikipedia.org/wiki/Absolute_zero) is –273.15°C, and it's not possible to be colder than this (at least [not in any meaningful way](http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146), and certainly not because of wind chill). The [coldest recorded temperature](https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on_Earth) on earth is around –90°C.

> **Comments:**
> **username_6**: Personally, I prefer -9e99 (or 9e99) as a dubious (and obvious) fill value. But yes, this is almost certainly what this is.  
> **username_7**: NASA often uses -9999... just to be sure they put the extra 9  
> **username_8**: the data on that page comes from weather underground, see http://www.wunderground.com/weather/api/d/docs?d=resources/phrase-glossary 'values will = -9999 or -999 for Null or Non applicable (NA) variables' I also suspect that 'feels like' is the heat index value, not the wind chill, which is why it's undefined ( you're not going to get heat stroke there at the moment )  
> **username_2**: @username_8 "feels like" is typically heat index in the warm season and wind chill in the cold season.  Some provides use additional factors in their algorithm as well.  
> **username_9**: Stupid languages that don't have an `NA` numeric value >:/  
> **username_5**: No, it isn't stupid. For analytical purposes spreadsheets necessarily have a numerical field, so we have to insert a 'stupid' number that we can recognize as spurious, and filter out when it comes to statistical analysis.  

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