Weather Data Sources

National Weather Service (NWS / NOAA)

We rely **exclusively** on weather data from the National Oceanic and Atmospheric Administration (NOAA), a scientific agency within the United States Department of Commerce. Specifically, we query the public National Weather Service API:

From this endpoint, we retrieve the localized CWA forecast office ID, along with the high-resolution grid coordinates (X, Y). We then fetch the raw grid data:

This gridpoint endpoint yields granular, hour-by-hour winter storm variables, including snowfall depth projections (in millimeters), sleet/ice accumulations (in millimeters), temperature, and wind speed.

U.S. Census Bureau Geocoder

To map arbitrary user inputs (like a 5-digit ZIP code or a town name) to geographic coordinates, we first consult our compiled local dictionary of major US cities and ZIP codes.

If a search query is not found locally, our server falls back to querying the official U.S. Census Bureau Geocoding Service, a free government resource:

This guarantees complete geographic coverage across all US states and territories, enabling any user to calculate their snow day probability, free of commercial tracking.

Caching & Freshness Schedule

To prevent overloading NOAA's public servers, and to ensure pages load in milliseconds (LCP < 1.5s), we utilize an aggressive caching hierarchy:

• Edge Cache: Calculations are cached at Cloudflare CDN edge nodes for 15 minutes. If multiple users in the same city query the calculator, they receive immediate, cached results.
• Data Freshness: After 15 minutes, the next query will bypass the cache, trigger a fresh background request to the NWS API, and update the cache.
• Geographic Indexes: State, city, and district coordinates are permanently compiled into our local server binary, loading instantly with zero external lookups.