Days 6-10 GFS versus ECM in Argentina for rainfall: Anomalous rainfall is projected into northeast Argentina in the 6-10 day period. We’re in an underachieving climate pattern to produce the rainfall so forecast confidence remains below average. The GFS is very wet with 6-8 times normal rainfall (~4 in. of rain) for the 5-day period indicated (Fig. 1). The ECM shifts the rainfall slightly east (and north) with less intensity (Fig. 2). Favoring the less wet ECM based on the strength of the mean subtropical ridge. The 11-15 day period shifts drier again. The longer term forecast through April is dry in Argentina. Therefore any brief wet weather interruptions may under-achieve.
Fig. 1-2: The midday GFS and ECM OP are compared for potential wet weather in northeast Argentina in the 6-10 day period.
Model Clustering Technique (for Europe): The 12Z GFS OP indicated a major temperature change in Southeast Europe to Southwest Russia with colder changes by 10-20F plus snowfall. Ensembles maintain the recent evolution of a warm pattern in this location. The model clusters for days 11-15 (Fig. 3-5) indicate the most likely (of 3) scenarios is an amplified upper trough over southwest/south Europe and deflated ridge to the east. This solution supports the colder change as the southern Europe storm track draws the cold in from the Western Russia source region. The Climate Impact Company week 2/3 ahead forecasts sided with the warmer ensembles but there is evidence to support a possible colder/snowier return in the extended-range.
Fig. 3-5: Model clusters for days 11-15 across Europe and the attendant 500 MB anomaly forecast.
Using the GFS Op versus GFS ENS: There is a lot of discussion on the volatile GFS and its consistent lowest skill score. The GFS ensemble is the average solution of 18 separate forecast members therefore always the “safe” forecast. However, if the pattern is going to change the GFS OP is likely the first model to catch that change. Is the change supported by climate signals is the usual technique to decide whether the change is correct.
Madden Julian oscillation: The ECMWF 14-day forecast indicates MJO may shift to phase_6 in 14 days (Fig. 6). Phase_6 is the West Pacific tropics. If so, the convection produced by MJO may grow intense due to the Kelvin Wave near the Dateline and cause upstream hostile weather in the U.S. Specifically, risk of excessive wet weather from Texas to Iowa would generate if MJO enters phase_6 and intensifies.
Fig. 6: ECMWF 14-day MJO forecast hints at phase_6 in 14 days.
