I can remember an similar occurrence down here in Southampton in around Feb ‘78 I think. I was at ArtCollege at the time and It had been bitterly cold for several days all week, with a hard frost most nights.
Then on the Thursday evening a group of us decided to attend an evening lecture starting at 7pm, so we adjourned to the Student Union bar at around 5.30. When we came out at about ten to seven, felt much milder and was starting to rain.
Sitting in the lecture theatre although there were no windows, I could hear the rain absolutely pouring down, and cascading from the guttering. After an hour or so, the sound of the rain diminished and then stopped. I thought no more of it, I just thought it would be very wet under foot on the walk back to the station after the lecture.
However, when the lift doors opened in reception, the sight through the glass walling was astonishing, huge amounts of snow on the ground and a near white with falling snow. It was impossible to get home for two days!