Atmospheric patterns, 700 MB and 500 MB height anomalies, statistical data, and various models such as the ECMWF monthly and weekly, NMME, IMME and the CFSv2, along with observed cases from past such months, data from 1895-2000 were used in this forecast.
Conditions transition from the cold phase to the neutral phase of the El Nino. The latest Nino 3.4 weekly sea surface temperature departures are at -0.1°C which puts us firmly in Neutral. ENSO-neutral conditions are expected to continue during May. The magnitude of the Real-time Multivariate based Madden-Julian Oscillation index is weak. However, there is some evidence of a re-emergence of the MJO across the Western Pacific by late April. Uncertainty in this signal is high due to potential Kelvin Wave interference with this potential MJO re-emergence. Due to the current weakness and uncertainty in its evolution, the MJO did not play a major role in the May 2025 outlook.
The IRI and North American multi-model ensemble indicate that ENSO-neutral will continue through the summer. The forecast team also favors ENSO-neutral, with chances well over 50% through summer 2025. In summary, ENSO-neutral is favored during the Northern Hemisphere summer, with a greater than 50% chance through August-October 2025.
The Arctic Oscillation is currently neutral and is predicted to remain near neutral to slightly negative as height anomalies across the Arctic are currently mixed and are predicted to remain mixed to slightly positive over the next two weeks. The North Atlantic Oscillation is currently neutral with weak but mostly positive height anomalies across Greenland and the NAO is predicted to remain neutral to slightly negative the next two weeks as height anomalies are predicted to remain weak but mostly positive across Greenland.
The Arctic Oscillation is currently neutral and is predicted to remain near neutral to slightly negative as height anomalies across the Arctic are currently mixed and are predicted to remain mixed to slightly positive over the next two weeks. The North Atlantic Oscillation is currently neutral with weak but mostly positive height anomalies across Greenland and the NAO is predicted to remain neutral to slightly negative the next two weeks as height anomalies are predicted to remain weak but mostly positive across Greenland.
The ECMWF weeklies depict strong positive height anomalies near the Great Lakes with above-normal heights across the central and northern states. Below normal heights are depicted across the southern states for week 1. A trough is forecast in the West for week 2—a zonal flow and above normal heights across the nation for weeks 3 and 4.
The ECMWF weeklies depict below normal temperatures for portion of the West Coast and the Southwest for weeks 1 and 2. Above-normal temperatures are forecast for the nation for weeks 3 and 4. The C3S and the Subx are similar.
TEMPERATURES
Yeloow-2-4°F
Orange-4-6°F
Red-6-8°F or Greater
Mediam Blue 4-6F Below
Dark Blue-6-8F or Great Below
Above-normal temperatures are forecast for the nation. Anomalies are expected to be 2-4°F.
PRECIPITATION
Yellow=-35%
Below
Brown-35-45% Below
Dark
Brown-45-55% Below
Light
Green-30-35% Above
Green-35-45% Above
Dark
Green-45-55%Above
Below-normal precipitation is forecast for the West Coast, the Southeast, the Mid-Atlantic and nearby areas of the Ohio Valley and the Northeast. The probability of occurrence is nearly 40 percent. Above-normal precipitation is forecast for the central Rockies, and most of the Plains. The probability of occurrence is up to 45 percent. The remainder of the nation is not expected to exceed normal climatology.
Jim Munley Jr.
http://www.jimmunleywx.com/jimmunleywx
Forecast Verification