Two weeks ago…
Let’s start with the bottom line: we got skunked. We ended up further west than we planned, out of position for the storm of the evening, and things did not come together at all like we’d hoped. I see two main issues with the evolution that happened vs. the forecasts:
- Clouds covered the target area for supercell initiation for too long
- The pre-frontal area got robbed of moisture at the last moment by the cluster of storms in western Oklahoma
I think the trajectory of the low, from the Four Corners north along the Front Range, played a factor. A bit more normal motion out onto the plains before heading north, and we would have seen a different scenario. Instead, things held off until the forecast storm line developed 40 miles or so east of the state line. We ended up going south at Copeland when we really should have gone east/northeast. At that point we were thinking more about staying out of the leading edge of the storm, when we should have tried to stay in front of it. But for that decision, we’d have been on US 56 right out ahead of the tornadoes that did form.
So is tomorrow’s setup different?
To look at the models, I’d say they forecast a line pretty much from the get-go…just as two weeks ago played out. But there are some differences…
Forecast rainfall is more spotty
Compared to a huge area of heavy precipitation, tomorrow is currently forecast to be more of a broken line. Here are two of the models’ forecasts for rainfall tomorrow evening (as of the Sunday night 7pm model run):
The trajectory and lifecycle of the low is much different
The previous deep low was still deepening as it ejected from Arizona and hugged the plains of Colorado on its way to western Nebraska and into Canada. This low will be in the process of becoming cutoff from the upper flow. It is forecast to travel eastward in the vicinity of I-70. It’s almost a more-typical lee-side low evolution, just somewhat north of where it normally happens. But as it moves east and cuts off from the upper flow the low will start moving southeast, and end up in the mid-Mississippi Valley mid-week. In my estimation this changes the orientation of the dry line and cold front in comparison to the low-level wind substantially. In fact some modeling even shows the front taking on a slight positive tilt after it passes I-135 (the south end moves a bit faster than the north end).
I’m a lot less gung-ho on this event than I was two weeks ago. But I also have to remember at this point two weeks ago I was considering pulling the plug on a chase. I don’t have a lot of confidence wither way, honestly.
As of where the models sit at this moment (11am Monday), here is where I’m watching as a potential chase target. Time frame would be between 5pm and midnight. Earlier initiation would mean more tornado risk; later would make the risk almost entirely straight-line wind. Still haven’t decided if I’ll chase, but I’m leaning toward it.