US Extreme Weather and Climate Change Dashboard

This site's headline detection metric for cold extremes: ETCCDI/CLIMDEX standard CSDI (Cold Spell Duration Index), run on NOAA's homogenized nClimGrid-Daily national series -- the direct cold-side analog of the Heat Waves page's WSDI, same homogenized-data reasoning (see that page's own note for why raw station records aren't preferred for trend detection). Unit: days per year, CONUS daily spatial mean.

ETCCDI/CLIMDEX standard definition (Zhang et al. 2005): annual count of days that are part of a run of 6+ consecutive days with an overnight low below the 10th percentile for that calendar day, against a fixed 1961-1990 base period -- the same definition this project's raw-station CSDI panel on this page uses, run here on NOAA's homogenized, gridded nClimGrid-Daily series instead of raw per-station data. See the Methodology page.

Source: NOAA NCEI nClimGrid-Daily (homogenized)

Computing trend…

IPCC AR6/ETCCDI standard TNn -- the single coldest overnight low observed each year, no percentile threshold involved. The direct cold-side structural analog of the Heat Waves page's TXx. Unweighted mean across raw, non-homogenized stations -- see the "Homogenized" TNn panel below for a NOAA-adjusted comparison. Unit: °C (annual min daily low).

The single coldest overnight low temperature observed each year at each qualifying station, averaged across stations. No percentile threshold or base period involved -- the simplest standard IPCC AR6/ETCCDI extreme-value metric, mirrored from the Heat Waves page's TXx. Reliable trend since 1895, independently confirmed against this metric's real station-count curve (same year as the heat-side metrics, same HCN network). Validated against a real, checkable event: San Antonio's station record shows TNn of -12.7°C in 2021, matching the real, documented February 2021 Winter Storm Uri cold wave (NWS-recorded low of -12.8°C) -- by far the coldest of its neighboring years. See the Methodology page.

Source: NOAA GHCN-Daily, HCN reference stations

Computing trend…

ETCCDI/CLIMDEX standard CSDI -- annual count of days in a run of 6+ consecutive days with an overnight low below a station's fixed-base-period (1961-1990) 10th percentile. The direct cold-side analog of the Heat Waves page's WSDI. Unweighted mean across raw, non-homogenized stations -- see the "Homogenized" CSDI panel at the top of this page (this site's headline cold-extreme metric) for a NOAA-adjusted comparison. Unit: days per year.

ETCCDI/CLIMDEX standard definition (Zhang et al. 2005): annual count of days part of a run of 6+ consecutive days with an overnight low below the station's calendar-day 10th percentile, against a fixed 1961-1990 base period. Reliable trend since 1895, independently confirmed against this metric's real station-count curve. Validated against a real, checkable event: San Antonio's station record shows CSDI of 7 days in 2021 (vs. 0 in each of 2019, 2020, and 2022) -- correctly and specifically flagging the real, documented February 2021 Winter Storm Uri cold spell, not a smoothed-away trend artifact. See the Methodology page.

Source: NOAA GHCN-Daily, HCN reference stations

Computing trend…

ETCCDI/CLIMDEX standard TN10p -- percent of days with an overnight low below a station's fixed-base-period (1961-1990) 10th percentile. The direct cold-side analog of the Heat Waves page's TN90p. Unit: % of valid days.

ETCCDI/CLIMDEX standard definition: annual percentage of days with an overnight low below the station's calendar-day 10th percentile, computed against a fixed base period. Direct analog of TN90p -- this project's own heat-side metric doesn't yet have a homogenized nClimGrid counterpart either, so neither does this one. This is an unweighted mean across raw GHCN-Daily stations -- no homogenization for instrument/station-move inhomogeneities, and no area-weighting for uneven HCN station density. See the Methodology page.

Source: NOAA GHCN-Daily, HCN reference stations

Computing trend…

ETCCDI standard Frost Days (FD0) -- annual count of days with an overnight low below 0°C. Unlike the other three cold-extreme panels, this is an absolute threshold, not relative to a station's history -- a directly actionable 'does the ground freeze' question. Unit: days per year.

ETCCDI standard index FD0: annual count of days with an overnight low below 0 degrees Celsius. An ABSOLUTE threshold, not percentile/base-period-relative -- unlike TNn/CSDI/TN10p above, this metric needs no base-period requirement, and answers a directly actionable question (does the ground freeze) regardless of whether that's locally unusual for a given station. See the Methodology page.

Source: NOAA GHCN-Daily, HCN reference stations

Computing trend…

A homogenized-daily-resolution comparison for the TNn panel above: same definition (annual coldest night), run on NOAA's nClimGrid-Daily national series instead of raw per-station GHCN-Daily data. Spatially averages across the whole CONUS before taking the annual min (unlike the per-station TNn above, which takes each station's min first) -- expect this series to read more moderate in magnitude; the fair comparison is trend direction/detection, not matching values. Unit: °C, CONUS daily spatial mean.

Same math as the per-station TNn/CSDI above (10th percentile, fixed 1961-1990 base period, 5-day window, CSDI's 6-consecutive-day rule) run on a different, homogenized, daily-resolution data source -- NOAA's pre-computed CONUS-wide spatial daily average, not a per-station reconstruction. Disclosed methodological difference: spatially averaging before taking the temporal extreme (this series) mechanically smooths day-to-day extremes relative to averaging each station's extreme afterward (the per-station approach) -- expect this series to read more moderate in magnitude even before any homogenization effect. The fair comparison is trend direction/detection, not matching magnitudes.

Source: NOAA NCEI nClimGrid-Daily (homogenized)

Computing trend…