A weather day is a calendar day on which weather conditions prevent productive construction work. Most commercial contracts grant time extensions for weather days that exceed historical normal expectations for the project location and time of year. The contract typically specifies the historical weather data source (NOAA records for the nearest weather station, often), the threshold for declaring a weather day (precipitation over 0.25 inches, temperature outside a specified range, wind speed exceeding a threshold, etc.), and the procedure for documenting weather days in real time.
Weather day claims require contemporaneous documentation: daily logs, photos, and weather data printouts for each claimed day. Claiming weather days at closeout based on memory rarely succeeds. Weather days are typically non-compensable: the contractor gets a time extension but no money, since the weather was equally outside both parties' control. Some contracts include weather contingency days in the original schedule (the contractor builds in 8 to 12 weather days per project), in which case only weather days exceeding the contingency trigger time extensions.