Before waxing the skis, some recognition of the chaotic nature of these long-term forecasts is needed. We start with the North American Ensemble Forecast System, which consists of 21 forecasts from the US Global Ensemble Forecast System and 21 forecasts from the Canadian Ensemble Forecast system. The plot below is known as a spaghetti diagram and includes contours of 500-mb geopotential height from all the members, along with a thick red contour for the ensemble mean. This chart shows that most ensemble members put a trough over the western U.S. but the coverage of spaghetti suggests quite a bit of variability in terms of placement and strength.
Moving to the gold standard ECMWF, I didn't have time to hunt down a spaghetti diagram this morning, but the mean of their ensemble also puts a trough in the west (note that there are slight variations in the time all these forecasts are valid).