The just out 0z run of the operational GFS model is the 3rd straight run that is not nearly as bullish as the models on Monday/Monday Night and previous time frames were. In 9 days, it crashes a strong system with a potent jet stream directly into the upper level head ridge and bashes it down/foreces it much farther west........going from the N.Plains back to the southwest US.
The heat ridge is unable to recover much as 5 days later another strong system crashes into the Midwest. er back into the Plains for a few days but gets bashed down again
Day 9 system below
fs_namer_207_200_wnd_ht | gfs_namer_207_500_vort_ht |
gfs_namer_207_1000_500_thick | gfs_namer_207_850_temp_ht |
Day 14 system below..........repeat of the the one from 5 days earlier.
gfs_namer_336_200_wnd_ht | gfs_namer_336_500_vort_ht |
gfs_namer_336_1000_500_thick | gfs_namer_336_850_temp_ht |
Here is the 0z run of the Canadian model ensembles, including the ensemble average at the top. Some members bash down the heat ridge/erode the northern 1/3rd of it......others use this strong jet stream coming out of the Pacific(especially strong by August standards) to pump up the heat ridge just to its south..........across at least the southern 2/3rds of the country.
If that strong jet buckles a bit out west, it allows for the upper level ridge downstream to get pumped up andhave a more northern location. It could also be mostly zonal along the Canadian border........or travel in a way that erodes the upper level heat ridge.
There WILL be a strong and widespread heat ridge, especially in the south.
There will be a seasonably strong jet stream, somewhere in the north.
360h GZ 500 forecast valid on Aug 16, 2018 00UTC
Forecasts for global GEM, control (GEM 0) and the 20 ensemble members