High Plains Drifter

The daily interrogation of the deterministic “control” run of the GFS in the 7 to 10 time frame is a good exercise of just how volatile the numerical models are at prediction in this time frame when it comes to trying to narrow down a chase “region” within our chasing domain — it really cannot be done. But it’s still fun, isn’t it? The whole anticipation “as the models turn”. Below is the new 5/15 run of the GFS. Look how different this deterministic GFS run is from the day before:

GFS 500mb:

GFS Surface:

The GFS now suggests that a significant “chunk” of the “off the west coast” deep trough will eject northeastward into the Rockies…supporting fairly robust development on the northern high plains. Should this verifiy verbatim, it most certainly looks like Dakotas chasing. The ECMWF and Canadian models (not shown), are much less impressive with such a scenario… with mean ridging continuing to be rather amplified over the Rockies…but enough flow atop the ridge over the far northern high plains… like Montana into the northern Dakotas for organized severe wx.

A much better way to try to draw “signal” out of the 7-10 day range is to use the ensemble approach. Below is a 4-panel of the GFS Ensemble forecast from the 5/15 12z run of 500mb height (570dam), 850mb Temp (20C), mean sea level pressure (1000mb), and Precip (0.25″):

Interpreting this 4-panel above… there’s a signal that something of significance may cut underneath the ridge…or “riding atop” the ridge, significantly squashing it inducing more westerly flow farther south (versus little flow at all near the ridge axis). The dark black isopleths on the ensemble 4-panel represent a mean of all the members.

So now it’s time to hit the dart board. A “consensus” of the two 5/15 GFS runs suggests the best chasing in South Dakota somewhere… so that’s where I’ll put today’s dart for Day 1 of the chase trip.