Did they factor in weather? You can go to Vegas or New Orleans and have ne'er-do-wells lurking about and walking the streets pretty much 365 days/nights a year. Memphis and Nashvlle, maybe not quite as many.
I'm guessing there are times in NE when even the most hardened street thugs get snowed in....
Thugs like cold weather. They can wear bulkier clothing to conceal weapons and stolen goods. They can wear a ski mask and not look out of place. They can wear multiple layers of clothing enabling them to shed the outer layer after a crime to avoid identification as the culprit.
During winter, they take advantage of earlier sunset and later sunrise to move about in the darkness for longer periods.