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Sources and Methods

Every source behind the facts on Knox Flood & Freeze, grouped by topic, with the date we opened it. Below the lists: how each calculated number is produced, and the wording our data providers ask us to include.

Updated

Knoxville facts

Tennessee law and licensing

Rules the estimator uses

National references

Data services

How the calculated numbers are worked out

  • Live weather: the newest National Weather Service observation from McGhee Tyson Airport (KTYS), the forecast for the City County Building, and active alerts for Knox County (TNC093). Observations and alerts refresh about every 15 minutes, the forecast every hour.
  • Rain against the normal: ACIS daily totals for the Knoxville Area record (McGhee Tyson Airport today), added up for yesterday, 7 days, 30 days and the month to date, next to the 1991-2020 NCEI daily normals for the same days. A trace counts as zero.
  • Flooding history: each day from January 1, 1871 to November 11, 2026 whose rain reached the 99th percentile of all daily readings (1.6 in.). Ranks compare a day with every other day; the wettest is ranked 1st. 16 days have no usable rain value (missing, or flagged as part of a multi-day total) and are skipped. Freeze nights are days whose low was at or below 20°F; winters run July to June. Monthly freeze averages use 1991 to 2020.
  • Flood claims by ZIP: every NFIP claim reported in one of Knoxville's 18 residential ZIP codes. Paid means building and contents payments added together. Loss dates are grouped by the date of loss FEMA reports. Any count under 5 reads "fewer than 5", with no dollar figure.
  • Hand checks before publishing: ZIP 37918's claim count (152) was queried directly from OpenFEMA, and the 5.08 inches on February 23, 2019 was read directly from ACIS. Both matched.

Data queries (pulled November 12, 2026)

  • ACIS StnData, full daily record: https://data.rcc-acis.org/StnData
  • ACIS StnData, 1991-2020 monthly precipitation normals: https://data.rcc-acis.org/StnData
  • OpenFEMA NFIP Redacted Claims v3, one query per ZIP: https://www.fema.gov/api/open/v3/NfipClaims?$filter=reportedZipCode eq '<ZIP>'&$select=reportedZipCode,yearOfLoss,dateOfLoss,amountPaidOnBuildingClaim,amountPaidOnContentsClaim,occupancyType&$top=10000

Statements from our data providers

  • Live observations, forecasts and alerts on this site are from the National Weather Service (weather.gov).
  • Daily station history is from ACIS, the Applied Climate Information System run by NOAA's Regional Climate Centers.
  • This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
  • FEMA on the NFIP Redacted Claims dataset: "This dataset is not intended to be an official federal report, and should not be considered an official federal report."

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