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So I was looking at the QCLCD hourly weather data from NOAA, and I noticed something weird about it. There's a column for hourly precipitation amount (HourlyPrecip), and there's also a column for the current weather condition (WeatherType). However, there appear to be many instances where the WeatherType reflects rain whereas the HourlyPrecip column does not show any rain.

Here's a sample of the data that shows the issue i'm talking about, for a particular station (NYC Central Park):

Date Time WeatherType DryBulbCelsius RelativeHumidity WindSpeed HourlyPrecip 20130801 951 -RA 22.8 71 0 T 20130801 1031 -RA BR 21.1 87 3
20130801 1047 -RA BR 21.0 81 5
20130801 1051 -RA BR 20.6 87 5 0.01 20130801 1120 +RA BR 20.0 90 0
20130801 1132 +RA BR 19.4 93 5
20130801 1144 -RA BR 19.4 93 0
20130801 1151 -RA BR 19.4 93 0 0.15 20130801 1159 -RA BR 20.0 93 6
20130801 1211 -RA BR 20.0 93 9
20130801 1219 -RA BR 20.0 90 6
20130801 1230 -RA BR 19.4 93 6
20130801 1251 RA BR 19.4 90 5 0.09

As you can see, these columns all indicate some degree of rain (RA) in the WeatherType column, but many do not show hourly precipitation.

Does the WeatherType reflect some sort of aggregated weather condition over a few hours, or is the data wrong (unlikely because this issue affects a large percentage of observations)?

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So I emailed the NOAA, and they responded pretty quickly with clarification (props to them!)

Q: My understanding of the "WeatherType" is that it is an "abbreviated 3-hourly weather observations" (from the QCLCD summary at https://data.noaa.gov/dataset/quality-controlled-local-climatological-data-qclcd-publication ). Is it more of a 3-hour summarized outlook of the weather, or a spot determination of rain/snow/haze etc?"

A: No, it's hourly, not 3-hourly. It's a spot determination at the time of observation.

As for the HourlyPrecip column, the measurements are only taken hourly, so there will only be measurements at 9.51, 10.51, 11.51, etc.

  • good job following up with them. Perhaps someday they will update/clarify that in their documentation. – Andrew - OpenGeoCode Mar 18 '15 at 20:36
  • yup, that was certainly confusing. at least the meteorologist who spoke to me was pretty helpful (even though the email seemed to be meant for ordering climatological data from them). – ethane Mar 18 '15 at 20:40
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I am assuming this QCLCD hourly dataset is for one weather station? The data are hourly samples by the station, The weather type on the othe hand (according to their documentation) is an "abbreviated 3-hourly weather observations"

Here is an introductory page explaining the content of their datasets:

https://data.noaa.gov/dataset/quality-controlled-local-climatological-data-qclcd-publication

If you look closer at this posted sample, at 10:51am a precipitation reading is made (0.01) and the weather type indicates light rain (-RA). At 11:20 and 11:32 observations are made that the rain is now heavy (+RA) with corresponding temperature, humidity and windspeed readings. At 11:44am the observation is that the rain is now light, with continues to 11:51 - one hour later where another 1hr accumulated precipitation is reported (0.15). You can also see throughout the sample, mist (BR) is also observed.

  • ah, thanks! I was looking at the PDF documentation and that did not explain what the "weather type" was (cdo.ncdc.noaa.gov/qclcd/qclcddocumentation.pdf). and yes, that data is for one particular station (NYC Central Park to be exact) - I've updated my question accordingly. – ethane Mar 18 '15 at 17:38
  • @ethane - I added some more to my answer to explain how to read the data. – Andrew - OpenGeoCode Mar 18 '15 at 20:30

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