Dear Erika,

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I always enjoy your exploits up in the land of perpetual midnight, or midnight sun, depending on the season. 

The extremes you deal with produce more challenges that most events ten times as long.

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More than for anyone else there, I bet Boston will be like heaven.

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No wonder there always seems to be large FBKS contingent there

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Makes me wonder how cold it has to get before you know you won’t be seeing any other runners out there though.

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Also, is there a handicap factor like the 3% /10-degree above 50 degrees for the colder side of 50 degrees?

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Your marathon ti.me is likely to slow by three percent for every 10 degree rise in temperature from 50 F. In other words, you'll run 3 percent slower at 60 F, 6 percent slower at 70 F, 9 percent slower at 80 F, and so on.
http://peakperformance.runnersworld.com/2009/09/sep-21-heres-how-to-pick-your-marathon-pace-if-the-weather-turns-warm.html