Weather anomaly index

How this is scored

Each location's daily rainfall, temperature range, and wind speed are compared to that same location's own trailing 30-day mean and standard deviation — a WMO SPI-style z-score, not a fixed global threshold. A score only qualifies once it clears both a real-world minimum (e.g. 10"+ of rain, not just "more than usual" for a desert) and a statistical rarity bar (z ≥ 1.5, roughly the top 7% of days for that location). Forecast-shift events instead measure how much a location's own forecast changed between consecutive ingestion runs.

Only locations with engine version 2 results are shown, so a scoring-methodology change never silently mixes old and new results in the same table. A short trailing history (fewer than 3 samples) falls back to a conservative fraction-of-mean estimate rather than a divide-by-near-zero spike.

This index is descriptive, not predictive — it reports what the data already shows, not what will happen. Official NWS alerts remain the authority for safety decisions; see the live alert banner on any location's forecast page.