Filter Time Series with Dates

Get the temperature for given dates using WeatherData. Create a new time series with specified MissingDataMethod to fill in missing data.

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data = TimeSeries[ WeatherData["Chicago", "Temperature", {{2015, 1, 1}, {2015, 12, 31}}], MissingDataMethod -> "Interpolation"]

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DateListPlot[data, FrameLabel -> Automatic]

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Use MinFilter with one-month range to analyze when the last and first freeze occurred that year.

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minF = MinFilter[data, Quantity[1, "Month"]];

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freezeline = {{minF["FirstDate"], 0}, {minF["LastDate"], 0}};

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DateListPlot[{data, minF, freezeline}, FrameLabel -> Automatic]

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First day after last spring freeze.

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spring = TimeSeriesWindow[minF, {"15 April 2015", "15 May 2015"}];

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DateObject[ First@FirstCase[ spring["Path"], _?(#[[2]] > Quantity[0, "DegreesCelsius"] &)]]

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First fall freeze.

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fall = TimeSeriesWindow[minF, {"1 Oct 2015", "31 Oct 2015"}];

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DateObject[ First@FirstCase[ fall["Path"], _?(#[[2]] <= Quantity[0, "DegreesCelsius"] &)]]

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