In addition, to the citation I gave that gives modeled North polar temperatures, this report gives actual TES measurements during Summer in Fig. 3:

Summer season variability of the north residual cap of Mars as observed by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES).
W. Calvin and T. Titus.
Planetary and Space Science
Volume 56, Issue 2, February 2008, Pages 212-22
http://dx.doi.org/10.1016/j.pss.2007.08.005

It shows 255K being reached as far north as 75N latitude, so would get even higher at the approx. 70N latitude of the Phoenix landing site.
The attached image below which is a blow up of Fig.1 from the report:

Factors Influencing the Location of Sustained Cold, Bright Spots in the North Residual Cap of Mars.
J. M. Pocock, W. M. Calvin
Seventh International Conference on Mars (2007), Abstract #3210
http://www.lpi.usra.edu/meetings/7th...7/pdf/3210.pdf

also shows 255K being reached at 75N latitude, so even higher at 70 N latitude.


Bob Clark

http://sitelife.space.com/ver1.0/Con...b443.Large.jpg