The stepping down in temperature that's taking place this week will result in a chilled end to October across the eastern half of the nation thanks to a deep trough that is setting up shop across Great Lakes this week and will reinforce itself next week.
October looks to end with temperatures that would be a few to perhaps several degrees below average if model guidance is correct. Both the European model's ensemble average and the GFS' ensemble average are in pretty solid agreement that a Novemberish airmass will camp out for much of the next two weeks.
As we stated last week, the coolest of cool would likely set up in the Lakes and Midwest -- and both the GFS and Euro continue to pounce on that concept as the core of the trough positions itself to our west. While we will be chilled, it will not be as cold as to places to our west will be. That said, we will likely see our first frost and freeze conditions of the season at some point in the next couple of weeks in many locations outside of the city.
The first brush towards frosts for a chunk of the region exists on Thursday through Saturday mornings -- Allentown has been modeled to get into the lower or middle 30's for each of those mornings, with upper 20's in the Poconos! The coolest mornings for South Jersey may not be until Saturday morning but even by Saturday one may have a shot at frost in the Pinelands.
The city's coolest morning over the course of the next week is modeled to be Friday where lows could get into the upper 30's.
After some recovery early next week, another front moves through and reinforces the chill in time for Halloween. Temperatures may even be a couple of notches cooler as we close out the month.