Earth Science community,

I've encountered a puzzling issue with a dataset from NOAA's Local Climatological Data Airports Database (which can be accessed here: https://www.ncei.noaa.gov/data/local-climatological-data/access). After converting the precipitation data from inches per hour to millimeters per hour, I noticed an abrupt and sustained increase in the mean values, (i.e mean monthly or monthly totals) starting in 2001 across all stations in the dataset.

The transformation applied was a straightforward conversion (1 inch = 25.4 millimeters), but the resultant values post-2001 seem abnormally high when compared to previous years. This is noticeable when plotting the data, which shows a significant jump in the mean precipitation amounts that don't align with historical trends.

The jump persists even without the conversion. This is clearly an artifact and not related to precipitation trends. The monthly values after 2001 are too high for mean monthly precipitation in New England Region.

Have there been any known changes in measurement techniques, data recording, or other methodological shifts at NOAA stations during this period that might explain this anomaly? Is it possible that a reporting change could have affected the data collection?

Any insights or tips on why there could be such a discrepancy or where to look further would be greatly appreciated. I am using the Airports Database since it has other variables in addition to precipitation that are relevant to my analysis.

Thank you for your assistanceTrends: See the difference before and after 2001


1 Answer 1


I'm using a quick NOAA tool to check precipitation values and I don't see any kind of jump in 2001.

I'm looking at "single station products", Boston Logan Airport, and precipitation (sum) from 1999-2005 to see monthly total precipitation. Then, averaging those monthly totals.

In 2001, I'm getting 2.56 (65 mm) inches precipitation per month, and your plot is saying closer to 100mm. I'm not sure where this discrepancy is coming from but you may want to check what you're averaging. I think your problems do not just start after 2001, but are high throughout your plots.

  • 1
    $\begingroup$ The long-term mean is about 87 mm/month at Boston it looks like, so the values pre-2001 don't seem too crazy. The discrepancy with 2001 (which indeed had 780 mm for the year -> 65 mm per month) could be something like average around January or using running averages. $\endgroup$ Commented Mar 27 at 10:40
  • $\begingroup$ (But yes, post-2001 is clearly off. Source used was the ever useful NOAA NOWData) $\endgroup$ Commented Mar 28 at 10:39

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