Seven Daily Profiles, Three, or None? Weekday, Day Type and Weather in the Daily Load Shape of U.S. Balancing Authorities (Cardinal Grid Notes, No. 2)

Methods that work on electricity load series rely on a notion of the typical daily profile, and practice differs on how many to keep: one per weekday, or one per day type (workday, Saturday, Sunday) with a list of special days. This note compares the alternatives on the public EIA-930 record of 44 U.S. balancing authorities (2015-07-01 to 2026-06-30, 172,741 BA-days), with profiles built causally from earlier days. Seven weekday profiles have a higher out-of-sample shape error than three day-type profiles in every BA; the length and recency of the reference history matter more than the calendar; fixed seasonal classes make things worse while the previous year's analog days help; and a three-class day type from daily mean temperature at one NOAA station per BA (heating below 59 F, cooling above 72 F) reduces the error by 14.6% with the previous day's temperature almost as good, so no forecast is required. Thanksgiving, Christmas and the two eves resemble Saturdays; Memorial Day, Labor Day and Independence Day resemble Sundays; four minor federal holidays are not distinguishable from ordinary weekdays. Code, results and figures are open. Web version and plain-language version: github.com/cardinalgrid/notes; cardinalgrid.com/notes.