May 18th and 19th Tornado Forecast

Good news and bad news with the 00Z NAM. Bad news is that tomorrow still does not look good for tornadoes. Good news is Saturday looks a whole lot better for tornadoes. I’m dragging ass and need to get to bed soon so I’m not going to get too in depth, but I wanted to get a post up. Above is my map showing where I think the best tornado potential is each day. Keep in mind I only highlight the area where I think the best chance is, not the entire area where it’s possible. I’m not SPC lol. I’m a storm chaser. I’m focused on where the best tornadic storm will occur and not much else.

Starting with tomorrow, moisture continues to look like the big problem. I ran through the NAM quite a few times looking at moisture advection from now through tomorrow afternoon and then meshed that up with current observations. It looks like dewpoints are going to be in upper 50’s and at best maybe a few low 60;s along the dryline and surface low by 7pm. That’s pretty weak for mid May and with surface temps getting into the 90’s along much of the dryline, I just can’t imagine that temperature-dewpoint spread is going to be manageable for tornadoes. So with too high of a temperature-dewpoint spread that kind of rules out the area south of far SW Kansas where surface temperatures are too high, which brings are focus farther north to where surface temperatures are lower off the northeast side of the surface low. This is where the bulge in the dryline/moisture wrap around the low curves back into Colorado. This bulge in the moisture gradient should be somewhere around Syracuse, KS. That’s the target I’ve been looking at. This area over the northern portion of the dryline and moisture wrap around are one area for storms and the other area is with storms coming off the foothills of the Rockies in central and north central Colorado. I didn’t look much at the foothills, so I’m going to skip over talking about that environment. From the quick glance I took I’d say it’s on par or maybe a hair lower with tornado potential when compared to the area just northeast of the surface low. So for now my focus in on the Syracuse, KS area and the areas adjacent to it along the moisture wrap around. Dewpoints are only forecast to be in the upper 50’s. That’s the biggest limiting factor for tornadoes right now. As I discussed at the beginning of this paragraph, I did take a fairly close look at moisture advection from now through tomorrow afternoon and for some reason the NAM is putting out a big blob of drier air over Oklahoma, that then advects up into that moisture wrap around corridor in SW Kansas and east central Colorado tomorrow. By 00Z the NAM shows slightly better moisture working into SW Kansas, but it looks like too little too late. The NAM does seem to have a good handle on current precipitation over Texas/Oklahoma, which seems to be the source of the drier air (and when I say drier I’m talking about ultimately a few degrees difference in dewpoints, but that can be a big difference as far as tornadoes are concerned). Current surface obs in the wake of those storms didn’t look terrible, but the NAM didn’t really show much drier air at the surface until 06Z either, so I’ll see how that unfolds. Long story short, as things look now I think we’re going to be a little short on moisture quality for a credible tornado threat tomorrow unless dewpoints are low with the NAM (which would be unusual) and we manage to get into the low 60’s tomorrow afternoon. I expect storms to develop in the foothills of Colorado and near the surface low and around the bulge of the moisture wrap around. For the bulge near Syracuse, I think that storms should come off discrete since storm motions are largely normal to the boundary in that area, but I think the’ll trend more outflow dominant with the weak low level winds and marginal moisture (less bouyant outflow). The NAM doesn’t show convection coming off the moisture wrap around area near Syracuse, it only has storms farther south along the dryline. I’m not buying that. The high resolution NAM has storms coming off the bulge/moisture wrap around area, but it also shows unfavorable convective evolution where storms seem to go outflow dominant and get clustered pretty quickly. That seems logical as far as convective evolution goes. That or the other scenario I could see is even if storms form later in the day and stay discrete into that 7-8pm window where LCL’s lower and low level shear picks up, I think CINH is going to beat those improvements out and still largely mitigate the tornado threat. So I guess pick your poison. Either scenario is bad for tornado potential and I think one or both are likely to happen. IF we do manage to get a tornado tomorrow in that area, it should be weak and most likely later in the day. I want to see what SPC says and look at current obs and CAM guidance before I make the call. My car is mostly packed and I’ll throw the rest of my stuff in there in the morning. I’ll be ready to go if I need to, but I’m 60/40 not going as things look now.

That was long a ramble on a shitty setup where I didn’t discuss a whole lot more than moisture and convective evolution lol. Sorry. I wing most of these blog posts and don’t even proofread when I’m done.

Alright, onto Saturday’s setup and better tornado potential. The NAM shows a much more volatile setup with the 00Z run. Despite this being a fairly major change from the last couple runs, I’m giving it a fair deal of credit because it is somewhat in line with the stronger setups with the models a couple days ago. So really this run is not that out of line if you look back over a few day stretch. The location has shifted relative to those earlier runs. A couple days ago it was showing the warm front and surface low (or at least the northern portion of the surface trough where winds back) was up near Omaha and across central Iowa. Now the surface low and warm front is down in north central Kansas and southeast Nebraska, but the same volatile environment is back along the warm front with high quality moisture pooling along the wind shift. Dewpoints are in the low 70’s with the 00Z, which would be great. The image below from COD shows the moisture pooling along this windshift/warm front running southeast from the surface low.

The thermodynamic side of the environment from the surface low southeast along the warm front looks great with deep moisture, low LCL/LFC heights, and strong instability. In addition to that, shear profiles look pretty damn good considering the strong instability we’ll have. Surface winds will be backing strongly along the warm front/E of the surface low, 850 winds will be fairly strong out of the SE around 25-30kts with 500mb out of the SW at around 40kts. That is strong directional shear with almost 90 degrees of turning between 850-500. Bulk shear is approaching 50kts. That kind of deep layer shear along with strong instability is a pretty volatile environment for supercells. I feel like I’ve seen this movie before. Assuming those parameters verify, that environment is quite favorable for tornadic supercells and storms should be explosive when they fire. This is not the type of setup you play downstream on. You get right up on the towers as they form because it probably won’t take long after one breaks the cap before it goes severe. When I say I feel like I’ve seen this movie before I’m thinking of the classic warm front demon supercell setups. Although deep layer shear is okay, SR upper level winds aren’t all that strong and being that these are warm front storms in a very moist environment along that wind shift corridor, I would expect them to trend HP pretty steadily through their life. That’s how these types of setups usually play out at least. They can be beautiful striated supercells early, plant a couple tubes and then go full demon mode as they transitions to HP. In my experience, you get on those storms early because they may only get down one or two easily visible tornadoes before it goes into HP beast mode. When that happens, you are going to get shit whipped by an expanding wind field at the surface if you try to go in the bears cage and hang out by the occlusion. I hate being in warm front demons when they transition. It’s violent lol. You can’t see shit without risking getting pounded by gorilla hail and it can be a bastard to drive if you stray a hair north or south (into the core or RFD). I’ll go in the occlusion on them, but it’s not a great time and it’s nerve racking as shit if you don’t want to beat the hell out of your car. If the storms do unfold that way and go HP, then they usually don’t produce much in the way of tornadoes once that HP mode really takes hold. They’ll have a beastly velocity signature, but the circulation will be broad and the gate to gate is always a little soft. As the wind field/circulation expands during that transition to HP it seems like a lot of people get duped into thinking it may be producing a massive tornado, but it’s not. It’s just a broad violent circulation that is unpleasant to be caught in, especially on muddy roads where you can get pushed into a ditch by the wind.

Alright, enough speculation and rambling for one night. You can see the areas I think have the best tornado potential each day on my map at the top. I am reaching pretty far here for Saturday’s setup considering how it hasn’t been exactly rock solid with the models, so take it with a grain of salt. I’m anxious to see how the 12Z run looks. I’ll probably post at least a brief update in the morning, so check back then if you’re interested.

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