[Met_help] A question

John Halley Gotway johnhg at rap.ucar.edu
Fri May 1 09:14:35 MDT 2009


I'm not sure I understand your question exactly, but when here's some information that may be helpful.

Here's the GRIB table definitions MET uses:

For precipitation, the code most commonly used is 61 for accumulated precipitation (APCP).  However, it sounds like you have data for GRIB code 140 for categorical rain (CRAIN).

I'd suggest checking in your forecast and observation files to see what types of precipitation data you have.  Is it APCP and/or CRAIN?

People most commonly verify forecast values of APCP against observation values of APCP.  When doing so though, you should make sure that the accumulation intervals match up - for example, compare 3
hours of forecast accumulation to 3 hours of observed accumulation, not 6 hours.  The MET PCP-Combine tool may be used to process your forecast GRIB files into the accumulation interval you'd like to use.

While APCP is most commonly used, you could verify CRAIN if you'd like.

You could compare a forecast of CRAIN to an observation of CRAIN.  When doing so, you should probably set the threshold value in the Point-Stat configuration file to be "eq1".  CRAIN consists of just
0's and 1's.  It's 1 where it's raining and 0 where it's not.  By choosing the threshold "eq1", you're interested in those points where it's actually raining.

Or you could compare a forecast of APCP against an observation of CRAIN (or vice-versa).  When doing so, you should threshold the APCP as "gt0.0" and threshold the CRAIN as "eq1".  By doing that,
you're comparing any non-zero forecast values of APCP against the observation values of CRAIN where it's raining.

I hope that answers your questions.  Feel free to write if you need more help.

John Halley Gotway
johnhg at ucar.edu

You can choose

zhxubinchaoshan wrote:
> When I use the Point-Stat Tool to calculate TS and ETS score,I found that the observation of precipitation in GRIB table is Categorical rain(CRAIN).And there is no the PARAMETER that is relate to the 3 hours or 6 hours cumulate precipitation. So if I want to calculate the Ts score of 3 hours or 6 hours cumulate precipitation, which observation variable I need to get from my observation files to match the CRAIN parameter?
> Thank you very much!
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