GFS and ECM Rainfall Forecast Bias across U.S. AG Belt

Climate Impact Company AG Hot Spot

Issued: Wednesday May 28, 2025

Highlight: GFS and ECM forecasts are too dry in U.S. AG Belt, MJO slower/stronger, and NCEP CAS soil moisture outlook.

Fig. 1-2: THE GFS and ECM precipitation bias during the past 30 days for the 15-day forecast.

Discussion: During the past month, both the GFS and ECM have produced dramatic too wet forecast bias across Southern Canada and too dry forecast bias across much of the U.S. AG Belt (Fig. 1-2). The ECM is also too wet on the U.S. East Coast. The May 2025 upper air pattern is plagued by the unusual presence of a persistent low-pressure area over the Mid-south States to the south of a blocking ridge pattern across Canada. The upper trough has propelled an exceptionally wet late spring centered on the Mid-south U.S.

Recent 14-day forecasts of the Madden Julian oscillation (MJO) have indicated strengthening as the MJO shifts toward and east of the Dateline in the equatorial region. Latest indications project moderate intensity in phase_6/phase_7 during the 8-14/11-15-day period (Fig. 3). In that position, MJO favors anomalous wet weather across the eastern half of the U.S. with a possible cooler forecast solution in the 11-15-day period. Additionally, support for wetter weather in South America and drier weather in Australia are developing (not quiet arriving).

Earlier today, the NCEP CAS soil moisture anomaly forecast for the summer season was issued. To reiterate, the primary concern for important dry soil conditions through early summer is in Iowa and the Southwest U.S. consolidating to Nebraska and Texas by late meteorological summer (Fig. 4).

Fig. 3-4: The latest 14-day NCEP MJO forecast and NCEP CAS soil moisture outlook for the end of June and August.