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Modeled trends in phenological advancement and sensitivity for three northeastern alpine species are less pronounced compared with lower elevations in the region, and this small shift in flower timing did not increase risk of frost damage. Potential reasons for limited earlier phenological advancement at higher elevations include a slower warming trend and increased cloud exposure with elevation and/or inadequate chilling requirements.

Mount Washington, New Hampshire, has the longest northeastern U.S. mountain climatological record (1930s to present), both at the summit (1914 m) and at Pinkham Notch (612 m). Pinkham's homogenized daily temperature exhibits annual (mean 5 +0.07uC/decade, p 5 0.07; min 5 +0.11uC/decade, p 5 0.01), winter (min 5 +0.18uC/decade, p 5 0.07), spring (max 5 +0.13uC/decade, p 5 0.10), and summer (min 5 +0.11uC/decade, p 5 0.01) warming trends. Though suggesting annual, winter, and spring warming (0.05 to 0.12uC/decade), mean summit temperature trends were not significant. Pinkham shows no significant change in date of first and last snow; however, the summit does but its period of record is shorter. Onset of continuous snow cover has not changed significantly at either site. Thawing degree days trended earlier at the summit (2.8 days/decade; p 5 0.01) and Pinkham Notch (1.6 days/decade, p , 0.01), but end of continuous snow cover trended significantly earlier (1.6 days/decade; p 5 0.02) only at Pinkham. Growing degree days showed no significant trends at either location. Pinkham exhibits more climatic change than the summit but less than regional lower elevations. Thermal inversions and high incidence of cloud fog commonly at or above the regional atmospheric boundary layer may explain the summit's resistance to climate warming. Caution is needed when extrapolating climate change trends from other mountains or proximate lower elevation climate data to upper elevations.

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