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James19991 t1_itzcy35 wrote

Technically it didn't at Pittsburgh International, where Pittsburgh's official weather observations are taken, but it's entirely possible it did at your location. You can still have frost too even if it doesn't hit freezing of course.


Yeuph t1_itziw47 wrote

How does that work? Frost without freezing?


James19991 t1_itzkvvh wrote

Official temperatures are measured 6 ft above the ground or so, and cold air sinks, so if it's 33 or 34 above the ground, it's totally possible for it to be 32 or 31 at ground level in certain areas.


LordApocalyptica t1_iu05jdn wrote

Also the heat exchange mechanism of phase change means that at a micro environmental level you can have phenomena like frost happening even if the ambient temp is slightly higher


KentuckYSnow t1_itzkw4b wrote

Temps at ground level can be a few degrees colder than just a few feet higher and dip below 32, at which point the vapor in the air can freeze.