Late summer ridge will bring return of warm weather to NYC

Put the pumpkin spiced lattes on hold.

A large ridge of high pressure is expected to build over the Central and Eastern United States late this week, with temperatures rising several degrees above normal. Most forecast models agree that this ridge will have staying power, hanging around for at least 7-10 days.

Ridging in the atmosphere can often be better conceptualized or defined as mid/upper level atmospheric high pressure. Higher pressure airmasses are lower in density by nature, expanding and allowing warmer weather to take over. The opposite is true for colder airmasses associated with troughing.

An atmospheric ridge of this size isn’t necessarily unheard of for September, but they can bring abnormally warm temperatures. Most model guidance suggests that while the ridge of high pressure is nearby, temperatures could average 6 to 10 degrees above normal.

If you’re thinking that warmth in September has been a trend of late, you’re correct. The last several Septembers have all featured a pattern of warmth in the Northeast states. In fact, the composite mid level height pattern from September 2007 through September 2018 has featured abnormal warmth across the entire Eastern half of North America.

Most model guidance agrees that the warmth will peak from late this weekend into early next week, as a large high pressure sits overhead and temperatures modify. But warmth may begin as early as this Wednesday, when high temperatures are expected to approach 90 degrees.

As we approach the middle of next week (7 to 10 days from now) there are some signals that the warmth will begin to back off, with temperatures returning to seasonable levels. We’ll be watching closely!