HDW, humidity, and wind, 1–3 days • Updated every 6 hours
All Locations Precipitation Outlook • Other locations: Flagstaff / KFLGMunds ParkBellemont
HDW (Hot-Dry-Windy Index) is the headline panel: vapor pressure deficit × wind speed, in units comparable to published HDW climatology. This product uses a surface-level simplification (2m humidity × 10m wind, converted to a 20-ft-equivalent reference height) rather than the textbook definition’s full lowest-500m vertical profile — a deliberate build-speed tradeoff, not the research-grade calculation. Higher values mean hotter/drier/windier conditions, i.e. faster potential fire spread if a fire starts; HDW does not predict ignition itself.
The relative-humidity panel marks each day’s afternoon (12:00–18:00 local) minimum explicitly, since that window is this climate’s typical daily low-humidity/high-fire-risk period. The wind panel shows sustained 20-ft-equivalent wind and gusts together with a compass-direction readout every 6 hours.
The dashed reference lines and this page’s alert-tier banner both use the wind and humidity thresholds from the Southwest Area Fire Weather Annual Operating Plan (2024–2027): 20-ft winds sustained 20 mph or greater, or gusting to 35 mph or greater, together with relative humidity at or below 15%, sustained 3+ consecutive hours. That operating plan actually defines its threshold using three simultaneous criteria, the third being an NFDRS adjective fire-danger rating; this product ingests no NWS or NFDRS products (by design, per this project’s scope), so the banner here reflects only the two model-derived criteria, not the full official definition. It does not reproduce, issue, or substitute for any official National Weather Service warning product — for that, consult NWS Flagstaff directly.
HRRR reports these fields at its native grid resolution (roughly 3 km), sampled at the nearest grid point to each site’s coordinates — not adjusted for the difference between that grid point’s modeled terrain height and the site’s true elevation. Unlike this product’s precipitation panel, that mismatch matters directly here: temperature, humidity, and wind are all terrain-sensitive fields, so a grid point at a different effective elevation than the actual site can read measurably hotter/colder or windier/calmer than conditions on the ground. Treat this outlook as area guidance, not a site-precise reading. No lapse-rate or terrain correction is applied.
See the Precipitation Outlook for this same location’s hourly precipitation and convective-ingredient guidance.