From earlier this week:
Sugar Season in the Fickle Mode
3/17/15 The thermometer which hangs in the shadow of our north facing woodshed is always quite accurate, even when the sun is shining. It shows the temperature has been oscillating between 31.5 and 32.5 for the last 16 hours. During this time the precipitation has turned from snow to rain (and everything in between) and back again more times than I could count. I don’t run the vacuum pump when the lines are choked full of ice, and had turned it off early last night when that happened. Then the temperature began rising to freezing again and I checked the pump room a few times during the night to see if anything was trickling into the sap release tank. I finally turned the vacuum on in the morning as the ice started to dissolve. In less than an hour the release tank, and upper manifold which directs the incoming sap lines into it, had completely filled with what looked like shaved ice. The releaser, under vacuum, had become a miniature snow-making machine. The sap was alternating between running through the slush one minute, and being choked off by it the next, making sap collection erratic and minimal. A mid-afternoon sudden drop in temperature accompanied by gusty winds and snow squalls finally put an end to this fickle behavior.
Sugaring has been described as the most weather sensitive crop in the world, and today is a good example of that. It would be hard to think of another crop where one degree of temperature would make such a dramatic difference in yield.