on Lake Champlain
Lake Champlain (and some adjoining ponds) has a classic abrupt ice out this year. 150 square miles of ice disappeared in two-three days, over half of it on the night of April 10th.
The above image was made on April 8th. It is cropped from a larger image. (http://www.erh.noaa.gov/btv/html/lake.php). The image is roughly 120 miles north to south.
There is ice cover on most of the lake other than the deep/wide center. There is noticeable darkening of the northern ice and some of it has gone out on the north western part (Rouses Point south to Isle La Motte).
The winter temperatures have been 1% above normal in terms of degree days. The lake froze over completely two or three times but never got to more than 3 or so inches thick before strong winds brought it to an end (see March 2 blog entry below). In late March we had a week of cold weather that halted the thawing process and gave the sun a little time to get into an even better position to thaw the ice. From April 6 to 10 we had a period of light winds and mostly sunny days with rising temperatures. On the last couple days it was warm enough to minimize the formation of overnight ice. A friend and I got out on the ice on the 9th (over a shallow, sandy bottom with dry suits and belay ropes). It held us up in some places and not others. On the afternoon of April 10th the wind was back.
The ice that had been quietly baking for five days was either blown into open water or crushed into itself by the wind. Once open water was created, waves broke the weak ice into individual crystals. The wind and waves also mixed the upper layers of the water column, bringing warmer, deeper water to the surface to provide the heat needed to melt the ice.
This NOAA picture was taken on April 12th. There appears to be a little dark ice in the northeastern part of the lake. on April 11th, I visited enough of these areas to conclude that about half of the ice had gone out on the night of the 10th.
This April 15th NOAA image shows no ice on the lake or northern Lake George. The brown color on parts of the lake is muddy water from the high water flows from snow melt in the hills. I confirmed that the southern part of Lake Champlain was ice free on the morning of the 12th and spoke to local people who said that it had been open on the morning of the 11th.
Bob
PS: The NOAA images provide a helpful view of that is going on with lake ice on a large scale. As they point out on their website, don't count on the images to tell you anything useful about the thickness or state of the ice.
