A somewhat rare numerical model role switch is underway at the moment. Regarding Sunday’s (9/18) chasing potential the GFS is actually more bullish than the NAM. Here’s the GFS sounding for Bedford county that afternoon at 21Z (5 pm EDT) from this morning’s model run:
Although this isn’t a ballistic setup these instability parameters are significantly stronger than the NAM is showing. With somewhat decent shear values this may mean that I haul out the chase gear Sunday afternoon.
The difference seems to lie in how each model handles the approaching cold front. The GFS shows the boundary well east of the mountains by nightfall while the NAM wants to slow down the frontal passage. Both models handle the associated upper level trough pretty similarly.
Regardless, I have my eyes on Sunday afternoon and will be watching the short range models closely as they come into play. I could use another chase (or two) before the season shuts down!