Source: The Washington Post - Link
There used to be a pattern to migration to the United States.
At the border with Mexico, there are a few natural limits to the process. One is terrain; some areas of the region are less hospitable to foot or vehicular traffic than others. Another is temperature. In El Paso, Tex., for example, the average high climbs from 59 degrees in January to 89 degrees in May — and keeps climbing.
Overlay the growing season in the United States, which drove a significant amount of migration, and what resulted was the consistent pattern under President George W. Bush that was three months of high migration (as indicated by the number of apprehensions at the border) and a slow tapering for the rest of the year.
The peak month of migration under Bush was March in every year except 2008. That year, the peak was in April.
Background for the “crisis” at the border. The pressures of migration will not respect borders. We’ve seen that in Europe. We’ll see it here.