Fall Chill to Replace Summer Heat in Northeast This Weekend

Tom Moore
Published: September 21,2016
As fall officially begins on Thursday, it will feel more like mid-summer across the Northeast, but some huge temperature changes will soon take hold across the region.
Several cities across the region encountered a top-five warmest climatological summer (June through August) on record. The pattern of well-above-average temperatures continued into September, and the next few days will feel more like early August.
The warmth, however, will come to an abrupt halt heading into the weekend as a cold front pushes through the Northeast.
(MORE: August 2016 Global Temperatures Set 16th Consecutive Monthly Record)

Temperature Change Timing and Impacts

Northeast Forecast Highs

Thursday
Fall officially arrives at 10:21 a.m. EDT, but it sure won't feel like it across most of the Northeast.
(MORE: Four Things to Know About the 2016 Fall Equinox)
With a few exceptions, the region will see temperatures in the low to mid-80s, which is about 10 to 15 degrees above average. The first hint of change comes to extreme northern New York and northern New England as a cold front sneaks southward across the border from Canada and temperatures begin to slide in these locations.
Much cooler air will slide southward behind the front.
Friday
The surge of cooler air continues to migrate southward through New York and New England. Highs behind the front will be in the 60s and 70s. The mid-Atlantic region will hold on to the heat just a bit longer, however.
Weekend
Cool air will have taken a firm hold across most of the region Saturday. Highs will be mainly in the 60s and 70s. The front will not move through cities like Baltimore and Washington D.C. until later in the day, so highs there will still reach the 80s.
You might want to keep a sweater or jacket handy if you are going to venture out on Saturday evening, as temperatures should fall off quickly.
(MORE: How Temperatures, Daylight 'Fall' From Late September to Late December)
Sunday will feature a chilly start with lows in the 40s and low 50s over most of the region. Parts of northern New York and northern New England could get down around the freezing mark, and scattered frost can be expected. Sunday highs across the region will be mainly in the 60s to the lower 70s.
Portions of northern New York and northern New England will see highs top out in the 50s, providing fall-like conditions.
Despite the significant temperature change, high temperatures will only be a few degrees below average for the date.

Northeast Forecast Lows

Setup For a Cooldown

As we move ahead to the end of the week, there will be a major change in the jet stream pattern.

A dip in the jet stream will allow much cooler air to move down from Canada into the Northeast.

A ridge of high pressure (bulge in the jet stream) that is responsible for the well-above-average temperatures will weaken and move eastward.
Meanwhile, a trough of low pressure (dip in the jet stream) will sink southward from Canada to replace the departing ridge.
This will allow much cooler air from Canada to move southward over the northeastern U.S. from late-week through the weekend.
Your wardrobe of shorts and t-shirts will be replaced by jackets and sweaters in many locations.
Looking ahead, it appears that the excessively warm temperatures that have been experienced across the Northeast will not return next week.
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