During May 2026, the prevailing upper air pattern featured an upper trough across western continent with a compensating ridge in the East. The upper trough was causal to heavy rain across central and eastern continent during May while the upper ridge warmed New South Wales. The wet pattern during May was primarily related to the proximity of the Madden Julian oscillation.

The western portion of the North Atlantic basin except for the Gulf of Mexico is shifting dramatically cooler. SSTA are extremely cool off the Northeast. The 7-day change is sharply cooler. Usually, large areas of cool SSTA bias the local climate cool.

The Madden Julian oscillation (MJO) shifts across the warm eastern equatorial Pacific during the next 1-2 weeks. U.S. climatology during an MJO phase_7 to phase_8 transition favors a cooler East U.S. regime. Although not super confident, the most likely (ECM ENS mega-cluster ensemble) upper air pattern in 15 days is a new upper trough centered on Ontario to deliver cooler weather into the East U.S.

The Asia/Bering Sea/North America (ABNA) index remains very positive and is the lead climate signal influence on the North America upper air pattern for the first half of June. The +ABNA regime is present when a strong trough is near the Bering Sea and compensated for by an upper ridge over East-central North America.