Signs of significant to major changes should take place across our region as we move through October with periodic chilly shots and increasingly stormy weather.
Two key players we always watch as we head into the winter season are the North Atlantic Oscillation better known simply as NAO and Arctic Oscillation (AO). We monitor both as they play a very important role in forecasting storm and cold cycles.
I won't get meteorological-crazy on you, so I will keep it simple. When the NAO is in the negative phase, it's usually a precursor for increasing storm chances for the Northeast. During the winter season I use this phrase, "When NAO is negative, think snow; when positive, less snow."
Right now, forecasting models are indicating that NAO is going sharply negative for the month of October, especially by mid-October. But since it's extremely rare to get snow in October, we are looking for more in the way of storms - not snow. Although I would not be surprised if the first wet flakes of the season fall in the Poconos sometime in mid- to late October.
The same can be said for the Arctic oscillation. When snow cover builds across the Northwest territories of Canada it creates high pressure, better known as Arctic air masses. This leads to a better chance of below-normal temperatures invading the Northeast. AO is also divided into positive and negative phases, as is North Atlantic Oscillation.
Negative phase with AO also leads to the better chances of cold and snow in the Northeast. During extreme negative phases, NAO and AO led to record snows in the past. The winter of 2009-10 was the snowiest winter of all-time in Philly with an incredible 78.7 inches; it was mainly attributed to record-setting negative AO and strongly negative NAO.
For this weekend, a strong cold front will produce a band of rain and perhaps scattered storms for Saturday morning into the early afternoon, followed by a chilly pop Saturday night (Poconos will drop into the 30s). Sunday will see a cool wind.
Look for a stormy period between Oct. 13-15, followed by a chilly blast with the first possible frost of the season.