The leading edge of the migration will advance as spring returns and milkweed emerges first along the Gulf states and then further to the north. "Citizen scientists" as far west as the Rockies and as far east as the Atlantic coast will track first observations of milkweeds, monarchs, eggs, and caterpillars and report their findings to Journey North who will post the information on interactive maps on their website. The maps are constantly being updated by folks who are posting updates from the field with the Journey North App or at their home computers on the Journey North website.
Here in southeastern Pennsylvania we may be lucky to play host to early migrants, the very same butterflies that originated in the north, flew south, and survived the spring migration north. At 40 degrees N, we may be seeing the first generation of monarchs from the eggs that were laid in the Gulf states. The trek northward is heavily influenced by weather (including fluctuating temperatures and various types and amounts of precipitation) and success of the first generation depends on the availability of milkweed.
I smile when I think of the excitement in kindergarten every spring as the leading edge advanced closer and closer to the Philadelphia area. Even my youngest citizen scientists were inspired by the thought of creating small wild spaces for monarchs, time and time again.
Last year I found my first monarch in Valley Forge National Historical Park on June 2 and tracked it several yards before it escaped view. Always makes my heart skip a beat to see those orange wings on a sunny spring day!