Wind Methodology

How the wind values shown on address, wind explorer, and PDF weather reports are derived — and how to read them honestly.

The one-sentence version

StormAuditor estimates the peak wind gust at an address by starting from the NWS analysis of record (URMA) and adjusting it with nearby measured evidence — airport-grade station gusts and measured storm reports — using a distance-weighted objective analysis, then reports the result as an estimate with its supporting evidence.

How SAWE-2 works

The current engine (SAWE-2.17) uses a two-pass Barnes/Koch objective analysis on top of the URMA gridded background. The correction denominator carries a fixed background-confidence term (0.25 on convective days, 1.0 otherwise) — StormAuditor's parameter, following the optimal-interpolation principle (Daley 1991) of retaining weight on the official analysis where nearby instrument support is thin. Observations are ASOS/AWOS station gusts plus measured, non-station-sourced Local Storm Reports — station-sourced reports are deduplicated so the same instrument never counts twice. The influence radius adapts to the storm regime: broad for tropical and synoptic events, tighter for organized convection, tightest for isolated cells — scales calibrated empirically against held-out measurements. A proportional cap keeps far-away readings from being transplanted onto an address, and an anomaly guard discards a lone extreme reading (100+ mph on a non-tropical day) that no independent instrument supports.

How it is verified

The engine is validated leave-one-station-out: each station's measured gust is hidden, the engine estimates that location from everything else, and the estimate is compared to the hidden measurement. The validated formula is exactly the one that ships — the greater of the local analysis value and the regional analysis field plus the capped two-pass observation correction. Validation cases are storm-active station-days across all 48 contiguous states over the trailing two years, all seasons; cases are never selected on the target station's own reading, and any co-located feed within 2 miles of the target is excluded from the evidence.

Engine changelog: SAWE-2.17 (Aug 2026) — the extreme-reading rule is now corroboration-only: any measured gust of 100+ mph must be supported by an independent instrument at 80% of its value within 50 miles that day to influence an estimate, in every weather regime (previously, archive-classified tropical days were exempt). All other behavior is unchanged from the previous version; the blind verification statistics below were produced under it and remain representative for all non-extreme cases.

What affects precision — the same factors any gridded-analysis product carries, disclosed rather than hidden: complex terrain can differ from its 2.5-km analysis cell, areas with fewer instruments lean more on the gridded analysis, and radar-derived evidence is sharpest near a NEXRAD site. Every report shows which evidence backed its value and from how far, so these factors are visible case by case instead of averaged away.

Current verification statistics (SAWE-2, 48-state LOSO, all-season)

Latest blind leave-one-station-out run (n = 763 held-out station-days, August 2024 – August 2026, all seasons): mean absolute error 6.4 mph, median error 4.3 mph, and 81% of estimates within 10 mph of the hidden measurement — blind accuracy competitive with published station-dependent analysis errors of 3–6 mph RMSE on non-blind stations. Where the engine proves its value is damaging-wind detection: the smoothed gridded analysis by itself captures only 45% of real 40+ mph station-days, while the engine recovers 65% of them at a frequency bias of 0.95 — meaning it flags almost exactly as many damaging-wind days as actually occur, neither inflating nor missing wholesale — with a critical success index of 0.50 versus 0.40 for the raw grid and 0.41 for a nearest-stations baseline. By design the engine stays conservative on the most extreme readings — a 60+ mph estimate is more likely understated than overstated. Statistics are refreshed whenever the engine or the validator changes.

How to read a wind value

Every number is an estimate at the property coordinates, not an on-site measurement. Every value is produced from the analysis background plus nearby measured gusts under the published, versioned methodology. See Wind Report by Address, the statewide Wind Explorer, and Limitations.