Every watt a data center draws ends up as heat, and the heat has to go outside into whatever the weather is. We mapped about a thousand data-center campuses in the United States and looked at the weather each one deals with: warnings in effect right now, drought, how many hours a year the outside air is cool enough to do the cooling, how many hours it's too hot or too muggy, and how often hail and tornadoes hit.
Campuses whose county is under a Weather Service warning, watch or advisory at this moment, the biggest first. Alerts refresh every few minutes.
The cheapest way to cool a server hall is to use outside air when it's cool and dry, and chillers are the expensive way. Evaporative systems, which cool by evaporating water the way sweat does, stop working well once the wet-bulb temperature reaches the mid-70s. Toward the upper left of the chart, the outside air does most of the cooling. Toward the lower right, the chillers and cooling towers are working hard.
The campuses come from OpenStreetMap: every feature mapped as a data center, grouped into campuses by site outline, by buildings inside the same site, and by distance. Operators, names and addresses are OSM's. Epoch AI's Frontier Data Centers database (CC-BY) adds power, GPU counts and construction timelines for the large AI campuses. Its sites are placed by ZIP code and matched to an OSM campus only when the operator, street or name agrees.
Megawatts are IT (critical) load, not what the campus draws from the grid, which is higher once cooling and losses are added. A figure is exact where OSM tags it or Epoch reports it. Everywhere else it's an estimate: floor area times a typical watts per square foot for that kind of building. Those estimates are marked with a ~ and are order-of-magnitude figures. Campuses mapped only as a point or outline have no figure at all.
Cooling hours are counted from the URMA 2.5 km hourly analysis at each campus's grid cell, the same data behind Threshold Hours. A free-cooling hour is one where the air is 65°F or cooler with a dew point of 59°F or lower, dry enough to feed a hall without drying or chilling it first. That limit comes from ASHRAE's recommended 15°C dew point for server inlet air. Wet bulb is calculated from temperature and dew point using Stull's formula. The 0.4% design value is the temperature exceeded only 35 hours a year, which is how engineers size cooling plants. Dew points are corrected against airport weather stations. URMA's most humid hours run 2–3°F too moist compared with the airport observations, which would inflate the muggy-hour counts by about half. So each campus's humid-hour dew points are adjusted using the median correction from its five nearest reporting stations (2025 METARs, within 150 km). Tested at 1,420 stations against their own observations, the correction cuts the design wet bulb's error by about a quarter and brings the average bias in muggy hours from +71 to near zero. Hours with a dew point under 58°F are left alone, so free-cooling counts are unchanged. The 1996–2024 normal and trend come from CONUS404, a 4 km reanalysis model. A model and an analysis of observations don't agree exactly, so read "vs. normal" loosely. URMA runs noticeably moister than CONUS404 in the humid South and East.
Hail is the largest MRMS radar-estimated hail (MESH) within about 1.5 km of the campus each year, the same grids as Hail & Roofs. Radar estimates tend to run larger than the hail that actually lands. Tornado odds are the county's chance per year that a given spot lies inside a tornado path, from SPC tracks 1995–2025 buffered to their recorded widths (Mobile Homes & Tornadoes). FEMA risk is the National Risk Index's expected yearly building loss from weather, per $10,000 of the county's building value. That's a measure for the whole county's buildings, not a rating for any data center. Drought is the U.S. Drought Monitor's category at the campus this week, plus the county's last 52 weeks. Alerts are live NWS alerts matched to the campus's county.