Temperature, wind, sky, sun, panel size, solution, application method. The math tells you how long the film will hold on the panel before it starts to freeze — and whether this is a panel to work right now, an elevation to wait on, or a day to run the interior route instead.
Methodology: freezing-point depression on IPA/water mixes, radiative cooling correction, wind-coupled surface temperature. Calibrated against the Twin Cities and Upper Midwest reference route. The math is in the methodology guide.
The math says you have 1 min 39 sec of freeze window on a panel that cleans in roughly 28 seconds — a ratio of 3.5× the clean time. The film will stay liquid through the squeegee pass; the solution's freezing point is comfortably below the working film temperature. Standard application, standard squeegee technique, no special handling beyond the routine cold-weather attentions.
The naive cold-weather rule is "above thirty-two degrees, work; below thirty-two degrees, do not." It is wrong in both directions. A shaded north-facing panel under a clear cold sky at thirty-six degrees ambient is at thirty degrees on the surface — pure water freezes on contact, and the operator wonders why. A south-facing panel in direct February sun at twenty-eight degrees ambient is at forty-two degrees on the surface — the same operator could work it all morning with the same solution if they understood the surface-temperature math. The thermometer reading is not the constraint. The glass is.