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October 28 through December 23, 2001 The average daily temperature at the Twin Cities International Airport exceeded the historical normal on December 9. This marked the 43rd consecutive day of above normal daily average temperature, a new record for the Twin Cities. The previous record for uninterrupted days of ABOVE normal daily average temperature was 42, observed in 1999 (November 4 - December 15), in 1998 (January 21 - March 3), and in 1987 (January 26 - March 8, 1987). The current streak began on October 28, continued throughout the month of November, and ended on December 23. The total streak was 57 days. A full month of above normal daily average temperatures (as seen in November, 2001) is a rare occurrence, but not without precedent. The historical data for the Twin Cities indicates that in four other months, all days within the month were ABOVE the daily average temperature normal: February 1998 January 1990 February 1987 March 1973 If we use the threshold, EQUAL TO OR ABOVE normal, the longest successive stretch of such days for the Twin Cites was 50. During a 50 day period, November 9 through December 28, 1923, the daily average temperature was EQUAL TO OR ABOVE normal. For purposes of this investigation, we've compared historical temperatures to the present-day standard for "normal". The present National Weather Service standard for daily normals is the use of 1961-1990 monthly temperature normals, fitted to daily values utilizing a cubic spline interpolation scheme. It requires just a single day to end a "streak". By not comparing historical data with their contemporary normals, we may have erroneously missed or included stretches of above normal temperatures. Our technique is particularly vulnerable when individual days are quite close to the norm.
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