Is Ice water a constant temperature?

Graphs always make results look rubbish.  Look at the slope on that!  The accuracy is great though - serendipitously, these were the thermistors I picked for my project.

My bet is no, it isn't.  I don't see how ice water could remain constant under non-ambient controlled temperatures (i.e. in a temperature controlled enclosure at 0C) because the ice is going to start melting straight away: at best, you can bring ambient water to a base temperature it will start to rise.  What you could measure is (a) with one thermistor, ambient temperature; (b) with second thermistor the rate of temperature change over time.  Plotting the ambient against temperature change by precise time you could probably calculate a rate of change, adjusted for fluctuating ambient.  I'd expect this graph to look like a slewed U: steep left stroke, and shallow right stroke.

I don't know what it's like in Canada at the moment, but here in the UK it is around 500C ambient so this experiment isn't even feasible for us!!

Ha, I also used ice water as an experiment when road-testing the Pico Datalogger with k-type thermocouples. It was far from constant, but all in plausible range. I did not think about stirring, but noticed when the probe touches an ice cub it gets colder. 

community.element14.com/.../picolog_data_logger_3

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Actually there might be something in that if you can tap a hole in the top put in the thermistor and seal it up so the flask can make a proper seal.  You may want a different flask though: destroying a hot pink one can't be worth it!

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Yes, it was insulated but I did not put a lid on to make it a completely separated environment from ambient. I figured, the cold air on top of the water would stay there as it is heavier than warmer air. 

As long as there is ice present and it stopped melting, the mixture should have settled at close to 0 degC, only exchanging energy with ambient through the glass and top.

PS: It is too warm on the Canadian east coast too, and humid.

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The ice part of the mixture is always below zero, while the water is always above zero, so I would assume the temperature of the probe depends on if it is touching ice and the gradient in the water around the rest of the probe surface. Maybe if you have slush (snow in water?) and you create a tiny pocket of water around the probe you could get just above zero, although impurities in the water could allow it to go below zero. So of course you need distilled water at sea level. 

My bet is no. The mixture of ice cubes and water is not a constant temperature.

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