Our scenarios brings us back to DCA. Right now in the wind and snow cover DCA is1-2 degrees differing from its surrounds. So we conclude from this snd past experience that wind homogenizes the situation. But, on a snow covered clear and windless night DCA will be 10+ degrees milder. Where is the warmth coming from?. Not the ground, it’s got 6” snow on it, not the surrounds as they are snow covered also. Are buildings leeching out that much heat? Improbable. So gonna lay it all in the Potomac? Go ahead. I don’t.
DCA is not a NWS facility but rather FAA. FAA wants conditions around the runway for the planes. Something about that is likely the culprit where wind has an effect on smoothing temps but radiational with low or no winds is artificially hampered..