Ahh, the wonders of long term forecasting.
The long wave trough currently situated across the western United States certainly does look to be moving out into the plains and upper midwest later this week, with emphasis on the Friday into early Saturday timeframe at this time when one considers all available model solutions. These solutions, of course, do leave quite a bit to be desired, which should be expected this far out, as everyone knows. But for some specifics... where the 12z runs of the major models are concerned: the ETA model maintains a positive tilt to the upper trough as it enters the plains Friday, with this nature resulting in quicker surface and upper air features when one compares the solution to the other models. Moreover...its tendency to move the dryline to the east so quickly may be overzealous considering its inability to resolve low level moisture profiles at such a range, when there is likely to be additional backing in the low levels in response to the increasing height falls, which could conceivably slow the dry lines' movement.
Considering, then, that the tendency for upper level troughs of this nature to slow and deepen is readily accepted, one leans toward the GFS model solution for the forecast of synoptic scale features. It should be pointed out that a major reason the ETA and GFS differ on their handling of the trough is the differences that exist in the models' solutions for the strength and amplitude of downstream ridging, an element directly tied to their handling of the upper low expected to develop off the coast of New England. It's here that the GFS gets my nod, which means that the overall pattern would slow and that the trough would have a more negative tilt as it emerges. Perhaps of greater importance when one is comparing the ETA and GFS today is the fact that the ETA suffered from a lack of RAOB data from the continental U.S. being ingested into the model due to problems with data flow to the supercomputer running the model. This in itself lends credence to a solution other than that of the ETA.
Of course, it does look like there will be plentiful moisture and instability available for active convection when the system does exit the Rockies, so its likely that someone....somewhere...is going to see some active storms late this week. The details will have to be hammered out as we move forward in time.
