10/04 Tornado Forecast


The fall tornado season looks like it very well may kick off tomorrow as a strong negatively tilted trough ejects into the plains. A surface trough draped north south through the plains will start to transition into more of a cold front overtaking a dryline in type surface pattern in the central plains surface pattern through the day. The map above shows the rough locations of the initiating boundaries in the central plains at 21Z.

Moisture return looks to be a little bit of a question mark. I haven’t forecasted much so I don’t have much room to talk here, but my guess is the NAM is overdoing dewpoints a tad. 00Z sounds at OKC and DFW show moisture depth is decent, but dewpoints are still in the upper 50’s with 60’s confined to south Texas. The NAM shows moisture return really ramping up with mid 60’s nosing into the target area by tomorrow afternoon though. With a strong low level jet I don’t doubt the NAM too much on moisture return, but like I said I think it’s probably juicing it a couple degrees. My only other slight concern for tomorrow is morning convection clearing out. The NAM and latest runs of the HRRR have it clearing out, at least over south central Kansas so I’m not too concerned. Even if it did geek things up a bit it would likely be further north so I’d adjust south if I needed to.

Minor concerns listed above aside, moderate instability should develop through the afternoon over north central Oklahoma and Kansas ahead of the surface trough. With a 50kt mid level jet nosing into south central Kansas during the afternoon, deep layer shear will be favorable for supercells. A very strong low level jet (40-60kts over the threat area) out of the south will create good length and curvature in low level hodographs and a tornado threat could become a possibility with any discrete or tail end storms tomorrow afternoon from central Kansas to central Oklahoma. If we get the mid 60 dewpoints with moderate instability, I don’t think a strong tornado would be out of the question given the respectable hodographs from central Kansas to northern Oklahoma. I’d just go 5% on the tornado probabilities in the initial Day 1 outlook if I were SPC, but if the NAM looks on track and the HRRR is showing several discrete cells from central Kansas into northern Oklahoma, then I’d probably up the tornado probs in a later day 1 outlook. For what it’s worth the NAM and 4km NAM have been pretty consistent with the precip pattern being more linear convection over northern Kansas with a transition to more of a tail end to the line in central Kansas and more discrete storms from there south into central Oklahoma ahead of the dryline (coverage gets sketchy in Oklahoma). That makes perfect sense to me given the surface boundaries and how similar patterns in the past have played out.

As far as targeting goes, I’m thinking I want to play the area where the cold front is starting to overtake the dryline. A lot of times that boundary intersection puts off the best tornadic storm with cold front/dryline setups (El Reno was a cold front/dryline triple point storm). It looks like that will be in central/south central Kansas (see my map). I think tornadoes are possible anywhere I boxed in on the map, but I’d put the greatest tornado threat over south central Kansas where storm mode tends to more discrete. This is where the best overlap over the mid and low level jet is, this is the area where you should transition from more strongly forced linear convection north to more discrete storms, this is the portion of the target area where sustained convection is more of a certainty. It’s also in the nose of the better quality moisture. Sooo, everything is pointing me towards a south central into central Kansas target. I may adjust that as surface boundary locations become more clear and we get short range CAM guidance. For now though I’m thinking Kingman is a good starting point. I marked my rough target with a star on the map.

As far as the extent of the severe threat goes, I think we could see some big hail, especially with the storms over south central Kansas and northern Oklahoma that tend to be more discrete and could be persistent supercells through the afternoon. I think there is a lower end tornado threat anywhere from north central Kansas into central Oklahoma, with the area most likely to see a few tornadoes being south central into central Kansas. I do think we’ll get some tornadoes tomorrow, just a matter of where. I don’t think this is a real good tornado setup, but with decent parameters across the board we may be able to eek out a strong tornado. I got the car loaded tonight so I’m ready to go. I plan on heading out a little after noon tomorrow and I’ll update again sometime before I leave. Sorry for the long rambling forecast btw lol. I literally just sat down and winged this one so I know it’s not my best work.


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