Forecast for Wednesday 4/17

A trough is forecast to deepen over the Rocky Mountains and move into the plains with a slightly positive tilt on Wednesday afternoon. Positive tilt troughs are usually not very good for tornadoes. Low level winds tend to veer more so you get less curvature in the hodograph, moisture gradients don’t tend to be as tight along the dryline, etc. Not a fan lol. This only looks like it’s going to have a slightly positive tilt though so the problems don’t appear to be that pronounced with this setup. And at least briefly the typical problems with a positive tilt trough start to vanish with the deepening surface low over the Texas panhandle. Through the first half of the day on Wednesday, 850mb winds are forecast to be veering badly, only backing during the afternoon as a surface low deepens over the Texas panhandle. Veering 850’s that back just in time is always a bit of a red flag for me. It usually doesn’t bode well for tornado potential. The focus for storms should be the triple point located near east central Texas or SW Oklahoma, the dryline running south from there and along the surface trough northeast of the triple point in NW Oklahoma where surface winds are forecast to back during the late afternoon/evening time frame. See the map where each of the three areas are depicted.

I think each of those three target areas is distinct so I wanted to run through each one in a little detail, but it’s super late as I type this and I need to get to bed so I’m going to just skim over my opinion for each target and leave out a lot of my reasoning as to why. SPC seems really confident in widespread storms. The NAM has been a little stingy, holding most storms off til later in the afternoon and not filling in the dryline much until around 00Z. Can’t trust the NAM on precipitation though so throw that out the window. I need to look closer at it, but my guess is the NAM is under-doing the storm coverage and timing. First with the triple point. Seems like the surest target for a decent supercell. The triple point should go up relatively early. I was a little concerned about quality moisture wrapping up in there tight, but it seems a little better with later runs. My biggest concern in this area for tornadoes is weak low level shear earlier in the afternoon when storms initiate. Below is a 00Z hodograph from the area near the triple point.

lol I mean that’s a very unimpressive little baby loop in the lower portion of the hodograph. Low level shear ramps up after 00Z, but the NAM is also showing a veer back veer tendency with hodographs at the same time as low level shear improves. Below is an 03Z hodograph from central Oklahoma.

You can see the lower portion of the hodograph is definitely better, but at the same time you get the backing immediately above that. That tends not to favor tornadic storms. So right now I think the triple point looks like it may have a chance for a tornado, but I think it will be lower end if it happens. I think the dryline south of the triple point down into Texas may have a chance at a little higher end tornado threat. This area has the best overlap of the mid and low level winds and the hodographs aren’t showing quite as bad of a VBV tendency in that 00-03Z window as the triple point does, so down south along the dryline you may get a window for a decent tornado threat with any discrete or tail end storms during the late afternoon/evening. And finally the third target I was looking at is the area northeast of the surface low along the surface trough where low level winds are forecast to back during the afternoon/evening. Up here storm motions will be more parallel to the area of convergence they’ll be forming along, so it will probably tend to fill in quickly. If surface winds back as forecast you may be able to get a lower end tornado with discrete storm. That being said generally the best bet is one of the first storms to go up and produce quick before storms fill in or some lead storm or one with maybe a break ahead of it that is more dominant. Basically I think storm evolution and things getting clustered in is going to be what inhibits tornado potential.

Still a long ways out, so I could be full of shit with my above guess at the three target areas I’m watching in the plains. I think I’m screwed for Wednesday. I have an important conference call I need to be on at 2pm. That makes the Texas dryline target a nonstarter for me. That is probably where I’d target if I didn’t have work obligations. I think it is a bit more of a gamble, but I also think it has the best tornado potential if things work out. Since I need to be at work until 2:30, I think I’m going to have to go with the NW Oklahoma target. Even with that target, I’m going to have to shag as out of work and hit the road as quickly as possible after I get off my call. We’ll see. Still a way out so things may change. I’ll be keeping an eye on it and will try to update regularly, so check back if you’re interested.

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