Surface and upper-air pairing

Sources & data notes

Surface inventory: NOAA NCEI Integrated Surface Database (ISD, historically ISH) station history, https://www.ncei.noaa.gov/pub/data/noaa/isd-history.csv (copy supplied to the build, not downloaded by this script). Upper-air inventory: NOAA NCEI Integrated Global Radiosonde Archive (IGRA) v2 station list, https://www.ncei.noaa.gov/pub/data/igra/igra2-station-list.txt (copy supplied to the build, not downloaded by this script). Both retrieved 14 September 2026. The pairing shown is by distance only. It selects the nearest upper-air site that satisfies the period filter above, and it is not a representativeness determination under 40 CFR Part 51 Appendix W. Proximity is not the test. Check terrain between the two sites, the elevation difference reported in each popup, and the surface characteristics of both locations before relying on a pair. A separation of a few hundred kilometres across flat terrain may be defensible where fifty kilometres across a ridge is not. Change the period filter and the pairing recomputes, because the qualifying upper-air set changes with it. With no period filter the nearest site is often one that stopped reporting decades ago. ISD is superseded. NCEI announced that it would not be updated beyond 2025-08-24. The file used for this build carries 8,985 records ending on that date and 2,194 more running past it, to a maximum of 2025-08-28. A record ending at the freeze was active then, not necessarily active today. Presence in either inventory does not mean the data are usable in AERMET. Confirm variables, completeness and sounding times in the station files before committing. Non-U.S. ISD data are subject to WMO Resolution 40 redistribution restrictions.