Here Comes Winter

The most critical ingredient to look at, to ensure that we have thunderstorms to begin with, is forecasted Convective Available Potential Energy, or CAPE. We begin with the forecasted CWASP chart from the GFS model, valid on Wednesday evening. Now that we know how this threat will set up, let’s go over the forecasted severe weather parameters on Wednesday evening. The forecasted CWASP chart for Wednesday evening peaks at over 85% in eastern Kansas, with significant values over 80% extending across Missouri and Oklahoma, even a bit into Texas. As the image tells you, percentage values over 65% tend to see the probability of significant tornadoes rise. These schemes have the advantage of being simple but they have the disadvantage of being bad at predicting branches whose behavior change over time. Could it really be that bad? 122 long-track tornadoes occurred in regimes similar to the one forecasted on Wednesday into Thursday.

Here, all hail, damaging wind, and tornado reports from all top 15 analog dates are combined into one picture, to give a view of where severe weather is most favored. The primary threats here will be damaging winds and hail; the linear shape of these storms should cut down on the tornado threat. A prediction of which one of two candidates will win an election is likewise worthless because the chances of accidental success are high. This kind of set-up is a consistently favorable one for severe weather in the Central US. In this forecast, off of the NAM model (which is notorious for exaggerating forecasted CAPE/instability), we see values on the order of over 3000 joules per kilogram of buoyancy extending from northern Texas, through central Oklahoma, and into central Kansas. We see an arm of the jet stream nosing into Oklahoma by Wednesday evening, which also sets up an area of divergence, as noted by the low wind speeds, over southern Kansas and northern Oklahoma.

That jet stream is barreling into North America at over 100 knots, and will be a big factor for Wednesday’s tornado potential. Now that we’ve evaluated all of the basic ingredients for thunderstorm and tornado formation, let’s move on to a couple less conventional forecasting methods. OK, the best bet now is that we will be in a neutral situation in the tropical Pacific. Let’s now turn our attention to the lower level jet stream, once again valid for Wednesday evening. What really grabs my attention, however, is the roaring subtropical jet stream entering Mexico and Baja California. We see the Pacific jet stream arcing over the ridge along the western coast of North America, contributing to that jet streak rounding the base of the trough in the Rockies. This lower level jet will be able to advect the warm, moist air from the Gulf, as well as the drier air from the west to create this potentially severe environment.

Model guidance is indicating that all of the wind shear, instability, and helicity in the atmosphere will have to contend with a warm layer above the surface, located just over 5,000 feet above the ground. This past winter, I began toying around with tornado data over the past decade or so, as well as the conditions they formed in. Fast forward a few months, and I was able to make a method that had great success in hind-casting tornado strength, before the storm cell and tornado even formed. The big caveat is that this model cannot predict if storms will form; it says that if storms do form and tornadoes are produced, that is the strength that the tornado should be. Another mathematical model I developed indicated a pretty high chance of significant tornadogenesis, with a strength of EF3 or greater, if storms do form. This is the first ‘red flag’, per se, that Wednesday evening could be a pretty tornadic environment for any storms that form.

Using the NAM model (which tends to exaggerate severe weather parameters), the environment over Oklahoma City, OK is favorable for tornadoes of EF5 strength on Wednesday evening. Next, let’s see how the upper air pattern looks, for the same Wednesday evening timeframe as the CAPE graphic we checked out. If you look at the animation, you will see it start with sudden cooling after a large sudden stratospheric warming in January. There is a large selection of vacation packages to choose from in Mexico: beautiful beaches, cool hotels and exotic historic interests. Showers are possible across the Northeast, as cool air produces small lake effect showers. A trio of systems will be producing a messy day today, with showers and storms making an organized appearance in the mountains. In other words, this is what one forecast model thinks the radars will see unfolding at 7PM Wednesday. If we look towards the Himalayan mountain range, however, we can see some oranges (and more recently, reds) bubbling up in the mountain range. Our weather modelling technique is a tool for greater understanding of species range dynamics and therefore vital to conservation planning for mobile species.