<p><a href="http://en.mimi.hu/meteorology/precipitable_water.html" rel="nofollow noreferrer"><strong>Precipitable water</strong></a> is the total amount of moisture throughout the air (the total in the entire tropospheric air "column"; most moisture is found in the lowest few km, due to decreases in temperature and density and where humidity sources being at the ground).  </p>

<p>Whereas <a href="http://glossary.ametsoc.org/wiki/Quantitative_precipitation_forecast" rel="nofollow noreferrer"><strong>QPF</strong></a> is the amount of precipitation that has fallen or is predicted to fall in a certain period of time (often 6 or 24 hours).</p>

<p>Generally more moisture (higher PWATs) do indicate the potential for more precipitation.  But you could definitely have a large PWAT and get no rain/snow/etc to fall from the sky.</p>

<p>I believe the greatest PWAT values are typically found in the warm saturated columns near tropical cyclones (hurricanes/typhoons).  From experience, in the US South, PWATs near/above 2 inches are generally considered quite large in the summer, and tend to indicate a greater chance of rain from air mass/sea breeze/frontal storms.</p>

<p>Whereas hourly rainfall rates can often be nearer 3-5 inches per hour, and locations can report over 20 inches of rain in a day<a href="https://en.wikipedia.org/wiki/List_of_weather_records#Rain" rel="nofollow noreferrer"> [rainfall records]</a>.</p>

CC BY-SA 3.0
2016-11-29T08:25:33.927Z
2016-11-29T08:25:33.927Z
JeopardyTempest
<p>When I take a look at weather models, there is an option to take a look at PWAT or QPF. What's the difference?</p>

<meteorology><models><water><precipitation>
What is the difference between Precipitable Water (PW or PWAT) and Quantitive Precipitation Forecast (QPF) in terms of computer weather model data?
user7060
# What is the difference between Precipitable Water (PW or PWAT) and Quantitive Precipitation Forecast (QPF) in terms of computer weather model data?

(Asked by: username_0 on 2016-11-28)

When I take a look at weather models, there is an option to take a look at PWAT or QPF. What's the difference?

**Tags:** meteorology, models, water, precipitation


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## 1 answers

### Answer by username_1 on 2016-11-29. Score: 4

[**Precipitable water**](http://en.mimi.hu/meteorology/precipitable_water.html) is the total amount of moisture throughout the air (the total in the entire tropospheric air "column"; most moisture is found in the lowest few km, due to decreases in temperature and density and where humidity sources being at the ground).

Whereas [**QPF**](http://glossary.ametsoc.org/wiki/Quantitative_precipitation_forecast) is the amount of precipitation that has fallen or is predicted to fall in a certain period of time (often 6 or 24 hours).

Generally more moisture (higher PWATs) do indicate the potential for more precipitation. But you could definitely have a large PWAT and get no rain/snow/etc to fall from the sky.

I believe the greatest PWAT values are typically found in the warm saturated columns near tropical cyclones (hurricanes/typhoons). From experience, in the US South, PWATs near/above 2 inches are generally considered quite large in the summer, and tend to indicate a greater chance of rain from air mass/sea breeze/frontal storms.

Whereas hourly rainfall rates can often be nearer 3-5 inches per hour, and locations can report over 20 inches of rain in a day [[rainfall records]](https://en.wikipedia.org/wiki/List_of_weather_records#Rain).


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