Snow ... frost.. typical May

Yesterday I woke up to snow covering my lawn, not too much but about 2 cm. This morning ~-4 dec C temperature, and it was cold.  Wend and inspected tunnels, after my wife indicated that doors are frozen in "big' tunnel.  Kicked the latch and opened, all seems to be fine, everything  looked ok.   Happy with this.  Bit worry about apple tree in full blossom and frost may cause some flower to be wasted, but I am optimistic that -4 was not cold enough to cause damage.