Mid-March to late April or early May is the standard window for northbound thru-hiking. A later start reduces any snowpack concerns, but amplifies the likelihood of encountering prolonged heat in the low country that predominates in the journey’s first half.
Following this schedule in '04 I encountered snowpack in the Huachucas, Rincons, and Catalinas above 8k, which was manageable due to the limited miles at high elevation here, and then again on the North Rim of the Grand Canyon, where it was deep and prevalent enough to warrant a roadwalk to Jacob Lake. I probably could have rejoined the trail again prior to Jacob Lake, as the snowpack did steadily diminish northbound from the rim, but the trail wasn’t particularly well marked back then. These days it may be better marked, but then again this year the snow may be especially noteworthy along the Kaibab Plateau.
In any case, given the choice between the inconvenience of occasional snow travel and the truly hike-sapping prospects of prolonged hot weather (and possibly drought), it seems prudent to choose the former, and thus to begin an AZT thru-hike earlier rather than later.
Incidentally, Chris Townsend chronicles his northbound thru-hike of 2000 in his book “Crossing Arizona.” Townsend began in early March of a drought year that saw one significant storm just prior to his start date at the border.
blisterfree