ECMWF And GFS Very Different

This morning there was a chilly west wind blowing along the Rillito wash, and skies were fairly dirty with suspended dust coming in from the west. This was particularly noticeable to the east, near the Rincon Mountains and south toward the Santa Rita Mountains. Looks like another dry week here in southeastern Arizona. However, after 6 days the global models seem to head off in opposite, out-of-phase, directions.

The ECMWF 168-hour, 500 mb forecast (above) is valid at 00 UTC Monday, April 2nd. The same forecast from the GFS is shown below (both are the operational member forecasts). The forecasts are very different from the central U.S., westward across the eastern Pacific. The GFS forecasts a closed 500 mb low over northwest Arizona with heights below 5400 m. However, the ECMWF forecasts a flat ridge in this area with heights around 5760 m - a difference of more than 350 m! Similar differences (but of opposite sign) are present along the north-central U.S. border and over the Pacific west of Canada. The forecast patterns remain out-of-phase like this for the 6 to 10 day period. Implications for weather conditions, particularly over the western U.S., thus depend upon which, if either, model has a better lock on the long-range synoptic pattern.