While sea-surface temperatures across the Equatorial Pacific Ocean are still running warmer than average, they have cooled slightly during the past couple of months. This indicates that the El Nino is beginning to weaken as expected.
The latest long-range climate models continue to show the El Nino weakening to a neutral phase by late spring or early summer and a La Nina possibly developing in the fall. This transition from an El Nino to a neutral phase could set the stage for a hotter summer across some parts of the central and eastern United States. This will have to be monitored over the next couple of months. As for the May temperature outlook, slightly above normal temperatures are forecast throughout the Northeast, Mid-Atlantic, Ohio Valley, Midwest, and eastern Great Lakes due to the weakening El Nino as well as a positive NAO (North Atlantic Oscillation) likely to be in place. Parts of the Pacific Northwest may also see warmer than normal conditions. A deficit of late-season heating degree days by between 20 and 40 is projected across the Pacific Northwest and the Northeast during the month of May. Meanwhile, portions of the Midwest, Tennessee Valley, and Ohio Valley are expected to see a bit of a surplus of early-season cooling degree days. Much of the Plains, Rockies, Desert Southwest, and Southeast will see temperatures average closer to normal during the month of May.