Model differences

The models seem to be settling on a scenario out to 6 days now, one that's favourable for our chase. However, at this time, I must state that the huge wildcard in the mix is moisture--that is, whether or not it'll be there in the abundance we seek.

After 7 days, though, they start to diverge and in a pretty fundamental way, one that would make for vastly different outcomes of the latter part of our chase.

The difference is outlined best by these two 500 mb forecast charts, valid next Saturday evening. The first one is from the GFS and the second is from the ECMWF.




At first glance, they appear pretty similar, both having upper circulations near the coast of California and another near New York City. But in between, the difference is huge.

The GFS has a positively-tilted lead trough over north Texas and the upper midwest, followed by a sharp short-wave ridge over Arizona. On the other hand, the ECMWF has a negatively-tilted trough over the northern plains followed by weak short-wave ridging in advance of the next impulse to be ejected. The difference is that the GFS solution would mean a longer time between storms and likely less low-level moisture availability, whereas the ECMWF solution would mean more low-level moisture and a near-constant barrage of storms, perhaps with a one-day break.

Forecasters far and wide perceive that the ECMWF is the superior model to all others in the mid-range. I have no lazy way of knowing if this is accurate; however, I do know that the wishcaster in me hopes that this is the case.