<p>I don't think a universal standard exists.</p>
<p>The US Weather Prediction Center, which is a part of the US National Weather Service, has a standard for its reporting of nationwide daily high and low temperatures. <a href="https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=nathilo" rel="nofollow noreferrer">The WPC deems</a> the daily high to be the highest measured / forecast temperature that occurs between one local midnight and the next, while the daily low is the lowest measured / forecast temperature between one local noon and the next. If the low occurs prior to midnight it is reported as the low for the following day.</p>
<p>On the other hand, <a href="https://www.weather.gov/ict/f6decode" rel="nofollow noreferrer">other parts of the National Weather Service (in this case the Weather Service Forecast Office for Wichita, KS) deem</a> the time from one local midnight to the next to suffice for both the daily high and the daily low. Many media in the US (e.g., <a href="https://www.chicagotribune.com/weather/ct-wea-asktom-0203-20190202-column.html" rel="nofollow noreferrer">the Chicago Tribune and WGN TV</a> similarly use midnight to midnight for both the daily high temperature and the daily low temperature.</p>
<p>Yet others use <a href="https://www.reddit.com/r/explainlikeimfive/comments/40ja0f/comment/cyumqzi/?utm_source=share&amp;utm_medium=web2x&amp;context=3" rel="nofollow noreferrer">one sunrise to the next</a> as the delineation. Weather forecasts in the media do use the term <a href="https://www.baltimoresun.com/bs-mtblog-2006-12-highlow_temperature_confusion-story.html" rel="nofollow noreferrer">overnight low</a>, typically referring to the low temperature between sunset and sunrise.</p>

CC BY-SA 4.0
2021-12-04T21:20:33.800Z
Both the high and low on climate reports are midnight to midnight for the NWS... see https://www.weather.gov/ict/f6decode
JeopardyTempest
CC BY-SA 4.0
2021-12-05T01:10:05.323Z
@JeopardyTempest But see https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=nathilo , which denotes the law as the lowest temperature from local noon to local noon.
David Hammen
CC BY-SA 4.0
2021-12-05T05:04:02.947Z
To be honest, I've never seen that product before.  I take it as some special product WPC issues... it also shows to change 24 hour precip by the time of issuance, which isn't how climatology does it of course.  But as far as I've ever known longterm official data is midnight to midnight.  And most forecasts are usually either midnight to midnight or morning low, daytime high (indicating any abnormally timed temperatures with arrows or words like falling and rising).  Will try to watch for the next big front to see how NWS does web forecasts, but I'm pretty sure it matches such.
JeopardyTempest
CC BY-SA 4.0
2021-12-05T05:06:34.593Z
It's disappointing such data are so very inconsistent... recently came to find after a lot of discussion that a local "climate" site had a large change with the 10 year recalculations... because the site only previously had 20 years of precipitation data (didn't use threadex, and the site had only added precip records a couple decades ago).  How highs and lows are determined should be right up front on historic data pages, and NOAA should have sites much more straightforward for station data downloads if they want to show reliability and clarity in data :(
JeopardyTempest
CC BY-SA 4.0
2021-12-05T06:06:39.823Z
I sent an email to NCEI to see if I could get further clarification... but I think for now it may be best to remove the line saying the US NWS has a standard, because our links seem to disagree :(
JeopardyTempest
CC BY-SA 4.0
2021-12-05T06:33:32.990Z
@JeopardyTempest Shall do. I should have said NOAA (which is the parent organization of the NWS). I'll also add references, including yours. I too find it a bit disturbing that (a) different organizations use different approaches, and (b) unless my google-fu has failed me, finding the approaches used by different organizations was nontrivial.
David Hammen
CC BY-SA 4.0
2021-12-07T09:30:03.527Z
Ok, after a response from Stuart Hinson at NCEI, the complex rules seem to have historical reasons that make sense.  COOP stations... which are stations that have tended to be manned by individuals/groups historically used simple [maximum/minimum thermometers](https://www.youtube.com/watch?v=1JSL4bdd_84), and so had to be checked during the daytime... I believe it may've been to allow plenty of wiggle time to check (because we all know every observer wasn't checking exactly at midnight every day)?  Or maybe there's more room for drift if left too long?  I think I learned once but forgot...
JeopardyTempest
CC BY-SA 4.0
2021-12-07T09:35:42.287Z
... one of those things I never thought I'd need again, manual instrument nuances! So the noon to noon COOP rule was a practical matter on the instruments once used. And that's all that was reported regularly, the daily summary. Now with digital setups (or regularly manned sites), midnight to midnight makes more sense to match the day. Of course he confirmed snowfall is 12 UTC-12 UTC... so yeah, our field is still a mess (see also the sludge of tropical cyclone methodologies around the globe).  So it is indeed inconsistent. I suspect some sites may've even changed forms over time :-/  Blah.
JeopardyTempest
CC BY-SA 4.0
2021-12-07T09:41:06.653Z
... one of those things I never thought I'd need again, manual instrument nuances! So the noon to noon COOP rule was a practical matter on the instruments once used. And that's all that was reported regularly, the daily summary. Now with digital setups (or regularly manned sites), midnight to midnight makes more sense to match the day. Of course he confirmed snow depth is 12 UTC-12 UTC... so yeah, our field is still a mess (see also the sludge of tropical cyclone methodologies around the globe).  So it is indeed inconsistent. I suspect some sites may've even changed forms over time :-/  Blah.
JeopardyTempest
CC BY-SA 4.0
2021-12-07T09:41:16.913Z
Though all this does actually help formulate an alternative answer to the users question, so thanks
JeopardyTempest
CC BY-SA 4.0
2021-12-03T16:33:11.117Z
2021-12-05T13:32:08.007Z
2021-12-05T13:32:08.007Z
David Hammen
<p>Yesterday I saw these day and night average temperature forecasts in my local TV weather report (see image below). I kept wondering if there are 'standard day hours' and 'standard night hours' for calculating these averages in the meteorological world, or are day and night hours determined solely by the forecast provider?</p>
<p><img src="https://i.imgur.com/1wRevi6.png" alt="Text" /></p>

<weather-forecasting>
Standard day and night hours in weather reports
Ingvar Lukas
# Standard day and night hours in weather reports

(Asked by: username_0 on 2021-12-03)

Yesterday I saw these day and night average temperature forecasts in my local TV weather report (see image below). I kept wondering if there are 'standard day hours' and 'standard night hours' for calculating these averages in the meteorological world, or are day and night hours determined solely by the forecast provider?

![Text](https://i.imgur.com/1wRevi6.png)

**Tags:** weather-forecasting


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## 1 answers

### Answer by username_1 on 2021-12-03. Score: 1 | Accepted answer

I don't think a universal standard exists.

The US Weather Prediction Center, which is a part of the US National Weather Service, has a standard for its reporting of nationwide daily high and low temperatures. [The WPC deems](https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=nathilo) the daily high to be the highest measured / forecast temperature that occurs between one local midnight and the next, while the daily low is the lowest measured / forecast temperature between one local noon and the next. If the low occurs prior to midnight it is reported as the low for the following day.

On the other hand, [other parts of the National Weather Service (in this case the Weather Service Forecast Office for Wichita, KS) deem](https://www.weather.gov/ict/f6decode) the time from one local midnight to the next to suffice for both the daily high and the daily low. Many media in the US (e.g., [the Chicago Tribune and WGN TV](https://www.chicagotribune.com/weather/ct-wea-asktom-0203-20190202-column.html) similarly use midnight to midnight for both the daily high temperature and the daily low temperature.

Yet others use [one sunrise to the next](https://www.reddit.com/r/explainlikeimfive/comments/40ja0f/comment/cyumqzi/?utm_source=share&utm_medium=web2x&context=3) as the delineation. Weather forecasts in the media do use the term [overnight low](https://www.baltimoresun.com/bs-mtblog-2006-12-highlow_temperature_confusion-story.html), typically referring to the low temperature between sunset and sunrise.

> **Comments:**
> **username_2**: Both the high and low on climate reports are midnight to midnight for the NWS... see https://www.weather.gov/ict/f6decode  
> **username_1**: @username_2 But see https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=nathilo , which denotes the law as the lowest temperature from local noon to local noon.  
> **username_2**: To be honest, I've never seen that product before.  I take it as some special product WPC issues... it also shows to change 24 hour precip by the time of issuance, which isn't how climatology does it of course.  But as far as I've ever known longterm official data is midnight to midnight.  And most forecasts are usually either midnight to midnight or morning low, daytime high (indicating any abnormally timed temperatures with arrows or words like falling and rising).  Will try to watch for the next big front to see how NWS does web forecasts, but I'm pretty sure it matches such.  
> **username_2**: It's disappointing such data are so very inconsistent... recently came to find after a lot of discussion that a local "climate" site had a large change with the 10 year recalculations... because the site only previously had 20 years of precipitation data (didn't use threadex, and the site had only added precip records a couple decades ago).  How highs and lows are determined should be right up front on historic data pages, and NOAA should have sites much more straightforward for station data downloads if they want to show reliability and clarity in data :(  
> **username_2**: I sent an email to NCEI to see if I could get further clarification... but I think for now it may be best to remove the line saying the US NWS has a standard, because our links seem to disagree :(  
> **username_1**: @username_2 Shall do. I should have said NOAA (which is the parent organization of the NWS). I'll also add references, including yours. I too find it a bit disturbing that (a) different organizations use different approaches, and (b) unless my google-fu has failed me, finding the approaches used by different organizations was nontrivial.  
> **username_2**: Ok, after a response from Stuart Hinson at NCEI, the complex rules seem to have historical reasons that make sense.  COOP stations... which are stations that have tended to be manned by individuals/groups historically used simple [maximum/minimum thermometers](https://www.youtube.com/watch?v=1JSL4bdd_84), and so had to be checked during the daytime... I believe it may've been to allow plenty of wiggle time to check (because we all know every observer wasn't checking exactly at midnight every day)?  Or maybe there's more room for drift if left too long?  I think I learned once but forgot...  
> **username_2**: ... one of those things I never thought I'd need again, manual instrument nuances! So the noon to noon COOP rule was a practical matter on the instruments once used. And that's all that was reported regularly, the daily summary. Now with digital setups (or regularly manned sites), midnight to midnight makes more sense to match the day. Of course he confirmed snowfall is 12 UTC-12 UTC... so yeah, our field is still a mess (see also the sludge of tropical cyclone methodologies around the globe).  So it is indeed inconsistent. I suspect some sites may've even changed forms over time :-/  Blah.  
> **username_2**: ... one of those things I never thought I'd need again, manual instrument nuances! So the noon to noon COOP rule was a practical matter on the instruments once used. And that's all that was reported regularly, the daily summary. Now with digital setups (or regularly manned sites), midnight to midnight makes more sense to match the day. Of course he confirmed snow depth is 12 UTC-12 UTC... so yeah, our field is still a mess (see also the sludge of tropical cyclone methodologies around the globe).  So it is indeed inconsistent. I suspect some sites may've even changed forms over time :-/  Blah.  
> **username_2**: Though all this does actually help formulate an alternative answer to the users question, so thanks  

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