I am calling for a “test run” intrusion of cold air the weekend before Halloween. But I also have concerns for storms in the Northeast/Maritime Provinces as well as Texas and Oklahoma.
The building of a ridge into Alaska this week and next will create a domino effect where a modified pool or Arctic air is forced south and east. Initially this air mass affects the Intermountain Region, then edges into the Great Plains/Texas, Mississippi Valley and Eastern Seaboard between now and October 31. I call this air mass a “test run” since you have not seen really cold weather in a long while. While likely not long-lived, the air mass change will give you a sense of what to expect when winter season settles in after Thanksgiving. A coastal storm that impacts the Eastern Seaboard (including NS/PEI and Newfoundland) this weekend will pull some cool air in behind it, but nothing out of the ordinary.
The night 40 deg F isotherm will probably get down to the Interstate 10 corridor at some point in the 11-15 day time frame. There will be a stronger storm that ushers in the colder air, a result of a merger of what is now Tropical Storm Norma and the cold front. Texas and Oklahoma will be targeted for heavy rainfall and severe weather before the colder regime arrives around October 25-26.
Most of November below the Canadian Border will be quite mild, and probably dry. But if we keep seeing -EPO and -NAO styled blocking ridges during and after the last week of next month, then colder and stormier times are likely along the southern and eastern tiers of the U.S. as we edge ever closer to the winter season.