Only a few changes to the going forecast (see previous posts for more detail). The NAM has hinted at it off and on for several days and now it is looking like a wide moisture gradient along northern portions of the dryline will in fact be a problem. Decent quality moisture with dewpoints in the 60’s currently resides over Oklahoma and SE Kansas. A surface low will deepen through the day tomorrow over northeast Colorado, drawing this moisture northwest into Nebraska. Dewpoints in the 60’s are only forecast up to around I70 immediately ahead of the dryline (with the moisture gradient widening north of there). When I looked at the wide moisture gradient problem a few days ago it looked like it was a result of the weak through that came through Wednesday veering low level winds in its wake. There just won’t be quite enough recovery time for decent moisture to tighten up along northern portions of the boundary by tomorrow afternoon. That being said, I’m looking at targeting a little farther south between I70 and Dodge City in Kansas where moisture quality immediately ahead of the dryline should be a bit better. Whether or not we get a storm along the dryline in that area is a bit of a question mark, but the NAM does want to break out discrete storms in that area. If a storm can get going, deep layer shear and instability should be adequate for supercells. Convective coverage or even getting a storm is the primary concern, but the HRRR should give us some guidance on that in the morning and if anything I think the NAM undershoots precip a bit in these situation. Assuming we do get a persistent storm in this area, I do think it could pose a tornado threat later in the evening as low level shear ramps up and LCL heights lower, but with only modest shear and overall mediocre parameters, I think the tornado threat will probably be lower end. Weird things happen in May though. I think the best tornado potential will be in NW Nebraska near the surface low tomorrow afternoon, but that is out of range for me given the tornado potential in south central Kansas on Saturday. It’s a solid 8 hour drive for me to NW Nebraska. Even if I got off a storm at 8pm up there I wouldn’t get home until 4am. That dog just ain’t gonna hunt when I’m looking at another long chase day Saturday, so I’ll play Kansas tomorrow instead.
No changes at all really to Saturday’s forecast. I do think strong tornadoes are a real concern, especially over the southern half of Kansas and western Oklahoma later in the day when low level shear ramps up. How badly morning storms work over our moisture and inhibit afternoon destabilization is the huge question mark for Saturday. The NAM has moderate instability developing in it’s wake, but dewpoints only manage to stay in the 60’s immediately ahead of the dryline up into central Kansas. That is keeping temperature dewpoint spreads wider than I’d like them, but it’s manageable I think from I70 south if the NAM is telling the truth. Anywhere dewpoints stay in the 60’s and we get at least moderate instability will be favorable for tornadic supercells capable of a strong tornado or two as low level shear strengthens through the evening. The latest NAM run is strongly suggestive of discrete storms over the area I boxed in red, and if storms do in fact remain discrete rather than filling in and going linear, then there may be a window right after dark for tornadoes that could be particularly dangerous. It is something that bears close watching. A subtle shift in the tilt of the trough and directional shear could change convective evolution so there is still a lot of uncertainty with this scenario. Additionally the complications with morning convection disrupting moisture quality and instability could easily railroad any tornado threat. I guess what I’m saying is that Saturday is looking like a very conditional threat, but I do believe the potential is there for a tornado outbreak with strong long-track tornadoes. I plan on chasing south central Kansas Saturday, probably starting near the border or just a little ways into Oklahoma.
I’m planning on working tomorrow morning and then I’ll take off around 11am to head out chasing. Good luck if you’re going out. I will probably update again right before I leave town so check back if you’re interested.