How is heavy rainfall determined in National Climate Assessment I'm trying to understand/reproduce/revise this chart in the Southeast section of the United States National Climate Assessment. The truncated scale for the bars is what caught by eye as a classic chart lie, but I'm also wondering about other features: different thresholds (besides 3 inches) and different aggregations (besides decades).



Original caption for this chart plus a map next to it:


  Figure 19.3: The figure shows variability and change in (left) the
  annual number of days with precipitation greater than 3 inches
  (1900–2016) averaged over the Southeast by decade and (right)
  individual station trends (1950–2016). The number of days with heavy
  precipitation has increased at most stations, particularly since the
  1980s. Sources: NOAA NCEI and CICS-NC.


The vague source citations are not particularly helpful, but I did find NOAA's Global Historical Climatology Network Daily downloadable data. That has daily precipitation data for 100,000 stations around the world, with about 12,000 in the Southeast. However, in a given year, I'm seeing 100 to 200 days with precipitation above 3 inches, but the chart indicates a different order of magnitude.

What does "days with precipitation greater than 3 inches" mean in this context?

I'm guessing there must be a "per station" part to it, but I still can't guess the exact math. The simplest treatment, a weighted average of each stations rate of heavy rain, produces the chart below.



It's close (same order of magnitude and peaks in 40s, 70s and recent), but not quite the same. Is there a different data source? Or a different treatment for irregular samples? Or a way to account for increasing number of stations?

Update after comments:
If I filter on stations with at least 110 years of data and use only years with 200+ days of data, I get the following, which is closer. (Using the same scale as the original, but avoiding bar truncation by just showing the tops.)



Most decades have lower values than the original.
After contacting the author of the chart, I believe the following defines the process behind the chart.


Data source: NOAA's Global Historical Climatology Network Daily station data for "PCPT".
Use only stations in the Southeast states which have data for 90% of days from 1895 to 2011, to match stations used previous edition of the climate report.
Use only years with at least 300 days of data.
Remove data values that have been flagged in GHND for quality issues.
Count the number of days of heavy rainfall (3 or more inches) for each station and year.
Using a 1° by 1° lat/lon grid, average counts of stations in the same grid cell.
Report the average of all grid cell-years for a given decade.


I have still not been able to reproduce the chart because I have had trouble getting clean data. Will update with a chart when that happens.