Forecast Products Overview
LMKwhen supports threshold-based alerting on NWS gridded forecast data via the National Digital Forecast Database (NDFD). Forecasts are extracted per location at ingest time and evaluated against your configured thresholds.
Available products
| Product | Unit | Description |
|---|---|---|
| Heat Risk | Index 0–4 | NWS experimental heat risk index |
| Snow Accumulation | inches | Daily snowfall total |
| Wind Speed | mph | Sustained 10-meter wind speed daily max |
| Wind Gusts | mph | Maximum 3-second wind gust daily max |
| Apparent Temp (high) | °F | Daily max apparent (feels-like) temperature |
| Apparent Temp (low) | °F | Daily min apparent (feels-like) temperature |
| Temperature (high) | °F | Daily max dry-bulb temperature |
| Temperature (low) | °F | Daily min dry-bulb temperature |
| Ice Accumulation | inches | Ice accumulation (seasonally available) |
Forecast days
Each product covers up to 3 forecast days:
- Day 1 — today's forecast
- Day 2 — tomorrow's forecast
- Day 3 — forecast for the day after tomorrow
Day boundaries follow NDFD convention: 06:00 UTC, not midnight. See NDFD Gridded Forecast Alerts for a full explanation.
Alert behavior
When a forecast value crosses your threshold for a given day, an alert fires. If a later forecast update worsens the value, a new alert fires. If the forecast improves and drops below your threshold, an all-clear is sent.
Each alert tracks forecast continuity — upgrades, downgrades, and reconfirmed values are all recorded in the alert timeline.
Polygon and circle locations
For polygon or circle locations, NDFD values are sampled at the centroid of the shape. Accuracy decreases as polygon size increases. A warning is shown in the alert rule wizard when any in-scope location is a polygon or circle.