At 5 p.m. Saturday, the temperature was in the 60s and a gentle breeze from the southeast was blowing at 9 mph.
An hour later, temperatures were plummeting, and winds from the northwest were gusting at 43 mph at Philadelphia International Airport.
Thus began the most-impressive wind siege of the year, and it is expected to persist until midafternoon Tuesday.
Gusts above 40 mph have been common, but arguably more impressive has been the mere persistence of the wind speeds.
Officially, the average sustained 24-hour wind for Sunday was 23.7 mph, and 23.6 for Monday, far and away the windiest two-day period of the year.
Jan. 23 held on to its title for the windiest day of 2016 at 24.8; you might remember that it had snowed quite a bit that day.
But the winds on the 22nd, 10.2 mp.h, and on the 24th, 9.7, weren't particularly impressive.
The gusts Tuesday morning haven't rivaled those of Sunday, and the forecast says that the weather should be safe for hats by late in the day.