Summer surface temperatures range from 13 to 20 °C and winter temperatures from 8 to 17 °C. (journals.plos.org)
In areas where summer surface melt exceeds winter snowfall, old interior layers in the ice sheet are exposed. (nsidc.org)
One interesting fact that I read somewhere is that the temperature peak at the bottom of the Aral Sea actually occurs in local winter, 100 % out of phase with summer surface heating. (theinconvenientskeptic.com)