<p>Since the question was referencing an aviation weather product (links no longer functional), there is a contextual answer as well.  The aircraft dispatcher for an airline flight must plan the flight according to FAA regulations, some of which apply to weather information. Only specific sources of weather observations and forecast products are authorized, and the "VALID" period must also be taken into account. </p>

<p>If I'm planning a flight that will depart at 1400Z and arrive at 1755Z, I am not authorized to use a forecast product that was issued at 00Z and is valid at 1800Z.  Even though this forecast product was issued prior to me starting to plan the flight, and thus is possibly the "most recently published product available", the product was produced for a specific valid period - namely, from 1800Z onward. I would have to reference as different product that was "valid" during my scheduled flight window. </p>

CC BY-SA 4.0
2018-11-26T17:30:34.670Z
2018-11-26T17:30:34.670Z
Jimmy
<p>The accepted answer correctly describes the meaning of the valid time for <em>point</em> forecasts, where a forecast is initialized at a particular time, and describes (is valid for) a second time. In this case, as the answer states, a &quot;valid&quot; time is the point in time that the forecast describes.</p>
<p>But this is not applicable to all NOAA products. Several forecast products describe a <em>range</em> of time, e.g. 3 hr precipitation forecasts, and these tend to be valid for the period <em>ending</em> at the valid time.</p>
<p>For example, the current 3 hour precipitation forecast from GFS states that it is valid at &quot;THU 04/11/24 15UTC&quot;. It looks like this:</p>
<p><a href="https://i.sstatic.net/WvZVO.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/WvZVO.png" alt="current 3hr precipitation forecast from GFS" /></a></p>
<p>If you load this forecast through the <a href="https://mag.ncep.noaa.gov/model-guidance-model-area.php" rel="nofollow noreferrer">Model Guidance</a> interface, you'll have access to the product information for each product. For the 3hr precipitation forecast, this information reads as follows:</p>
<blockquote>
<p>Accumulated precipitation in inches for the 3 hour period <strong>prior</strong> to the forecast hour expressed as color fill. A reference bar of values for each color is located on the left side of the image. [emphasis mine]</p>
</blockquote>
<p>The same appears to hold for most other products that describe a period of time rather than a point. However, I would recommend always checking the product description and model guidance documents where available, as they will often clarify the relevant meaning of &quot;valid&quot; and other terms in the forecast.</p>

CC BY-SA 4.0
2024-04-11T17:02:17.117Z
2024-04-11T17:02:17.117Z
adamf
<p>Short answer: <strong>Valid</strong> just means the expected conditions at that certain time.</p>

<p>In your <a href="https://www.aviationweather.gov/data/products/turbulence/20181028/16/20181028_16_F00_gtg_170_total.gif" rel="noreferrer">example</a> the map shows a forecast of 00 hours which is <strong>valid</strong> for 0600 UTC. Basically it means that the forecast/simulation is initialized on 0600 UTC and because the forecast time is 00 hours this forecast is also <strong>valid</strong> for 0600 UTC.</p>

<p>NOAA also provides forecasts for several hours (or days depending on the product). In this case, your simulation may be initialized on 0600 UTC but if you want to see what the conditions on 1500 UTC are you have a forecast of 09 hours which is <strong>valid</strong> for 1500 UTC. See <a href="https://i.sstatic.net/6AhJF.gif" rel="noreferrer">this example</a>.</p>

CC BY-SA 4.0
2018-10-29T07:49:49.243Z
Right on.  Dyneken when NOAA issues a warning/watch/advisory (including a SIGMET I believe), it's for a time window.  But for a general value forecast/graphic, they are typically for a specific time.  Valid on such products basically means "at that moment, the conditions are expected to be..."  If you want to get an idea of what to expect at 0630Z... you would want to look at the 0600Z product and the 0700Z product, and it will probably be somewhere in between those two hours if the forecast is good.
JeopardyTempest
CC BY-SA 4.0
2018-10-31T20:32:05.230Z
Bollenhek - great, much clearer now.  And JeopardyTempest -very good to know about interpolation between valid times.  Thanks!
Dyneken
CC BY-SA 4.0
2018-10-29T07:30:25.273Z
2018-10-29T07:37:48.493Z
2018-10-29T07:37:48.493Z
Bollehenk
<p>NOAA weather forecast maps often include a valid time period, e.g:  &quot;valid from time1 thru time2.&quot;  However, many maps only indicate a single time, e.g: &quot;valid time1.&quot;  In the absence of other information, does this typically (or officially) mean valid up until time1, or valid after time1?</p>
<p><a href="https://i.sstatic.net/iCSJQ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/iCSJQ.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2018-10-28T01:28:50.373Z
Welcome to SE Earth Science! Might I ask which products you are looking at? Maybe include a URL?
BarocliniCplusplus
CC BY-SA 4.0
2018-10-28T01:30:56.977Z
Generally, it is used to add context to a map, so that it is representative of a given time or a forecast made on a specific date. But without seeing the type of product, it is hard to determine which case it is.
BarocliniCplusplus
CC BY-SA 4.0
2018-10-28T18:11:35.067Z
Sure - links added in Edit
Dyneken
<meteorology><national-weather-service>
What's the default meaning of "Valid" in NOAA weather map?
Dyneken
# What's the default meaning of "Valid" in NOAA weather map?

(Asked by: username_0 on 2018-10-28)

NOAA weather forecast maps often include a valid time period, e.g: "valid from time1 thru time2." However, many maps only indicate a single time, e.g: "valid time1." In the absence of other information, does this typically (or officially) mean valid up until time1, or valid after time1?

[![enter image description here](https://i.sstatic.net/iCSJQ.png)](https://i.sstatic.net/iCSJQ.png)

**Tags:** meteorology, national-weather-service

> **Comments:**
> **username_1**: Welcome to SE Earth Science! Might I ask which products you are looking at? Maybe include a URL?  
> **username_1**: Generally, it is used to add context to a map, so that it is representative of a given time or a forecast made on a specific date. But without seeing the type of product, it is hard to determine which case it is.  
> **username_0**: Sure - links added in Edit  

---

## 3 answers

### Answer by username_4 on 2018-10-29. Score: 8 | Accepted answer

Short answer: **Valid** just means the expected conditions at that certain time.

In your [example](https://www.aviationweather.gov/data/products/turbulence/20181028/16/20181028_16_F00_gtg_170_total.gif) the map shows a forecast of 00 hours which is **valid** for 0600 UTC. Basically it means that the forecast/simulation is initialized on 0600 UTC and because the forecast time is 00 hours this forecast is also **valid** for 0600 UTC.

NOAA also provides forecasts for several hours (or days depending on the product). In this case, your simulation may be initialized on 0600 UTC but if you want to see what the conditions on 1500 UTC are you have a forecast of 09 hours which is **valid** for 1500 UTC. See [this example](https://i.sstatic.net/6AhJF.gif).

> **Comments:**
> **username_5**: Right on.  username_0 when NOAA issues a warning/watch/advisory (including a SIGMET I believe), it's for a time window.  But for a general value forecast/graphic, they are typically for a specific time.  Valid on such products basically means "at that moment, the conditions are expected to be..."  If you want to get an idea of what to expect at 0630Z... you would want to look at the 0600Z product and the 0700Z product, and it will probably be somewhere in between those two hours if the forecast is good.  
> **username_0**: Bollenhek - great, much clearer now.  And username_5 -very good to know about interpolation between valid times.  Thanks!  

---

### Answer by username_2 on 2018-11-26. Score: 2

Since the question was referencing an aviation weather product (links no longer functional), there is a contextual answer as well. The aircraft dispatcher for an airline flight must plan the flight according to FAA regulations, some of which apply to weather information. Only specific sources of weather observations and forecast products are authorized, and the "VALID" period must also be taken into account.

If I'm planning a flight that will depart at 1400Z and arrive at 1755Z, I am not authorized to use a forecast product that was issued at 00Z and is valid at 1800Z. Even though this forecast product was issued prior to me starting to plan the flight, and thus is possibly the "most recently published product available", the product was produced for a specific valid period - namely, from 1800Z onward. I would have to reference as different product that was "valid" during my scheduled flight window.


---

### Answer by username_3 on 2024-04-11. Score: 1

The accepted answer correctly describes the meaning of the valid time for *point* forecasts, where a forecast is initialized at a particular time, and describes (is valid for) a second time. In this case, as the answer states, a "valid" time is the point in time that the forecast describes.

But this is not applicable to all NOAA products. Several forecast products describe a *range* of time, e.g. 3 hr precipitation forecasts, and these tend to be valid for the period *ending* at the valid time.

For example, the current 3 hour precipitation forecast from GFS states that it is valid at "THU 04/11/24 15UTC". It looks like this:

[![current 3hr precipitation forecast from GFS](https://i.sstatic.net/WvZVO.png)](https://i.sstatic.net/WvZVO.png)

If you load this forecast through the [Model Guidance](https://mag.ncep.noaa.gov/model-guidance-model-area.php) interface, you'll have access to the product information for each product. For the 3hr precipitation forecast, this information reads as follows:

> Accumulated precipitation in inches for the 3 hour period **prior** to the forecast hour expressed as color fill. A reference bar of values for each color is located on the left side of the image. [emphasis mine]

The same appears to hold for most other products that describe a period of time rather than a point. However, I would recommend always checking the product description and model guidance documents where available, as they will often clarify the relevant meaning of "valid" and other terms in the forecast.


---

