2014-04-23 FCST: TX/OK/KS/NE

[Marcus Diaz]

I'll get the discussion rolling on this day because I'm conflicted on what I'm seeing. First off, I know there's been run-to-run discrepancies with the GFS on different aspects. Mainly, the moisture. It appears this might end up being a case of "just in time" moisture, which usually means this could be a case of shallow moisture. The GFS has stuck to a pretty general location of the dryline; roughly from Midlannd-Pampa-Oakley-Kearney. During the day it appears only low 50s dews before the LLJ cranks in and pushes some mid 50s right on the DL, with 60s just a couple dozen miles east in parts of KS. The NAM is less bullish with the moisture, putting only upper 40s to mid 50 dews on the DL. The LLJ has been consistent in being pretty strong from the northeastern TX PH through S NE in the order of 40-50kt. While the main trough is centered further north, there's still some vort lobes rotating around the southern fringe into our target area. We should be good enough on the mid levels for supercells. While CAPE isn't spectacular thanks to the low dews, its appears there should be enough with the daytime heating to get over 1,000-1,500 j/kg SBCAPE. So 2 things really bother me about this setup. 1 is obviously the entire issue with moisture. 2 is how the CINH fills in right at 0z. The positives from this setup is the great wind profiles all the way up. The hodographs have been looking beautifully curved clockwise in the areas with the best LLJ. Also the GFS has consistently broken out some precip the past few runs.

Overall this is a pretty piss poor setup. But thought I'd open up the discussion because I'm in no way a forecasting expert.

 

[Matt Hunt]

With the 12z NAM, I'm starting to reconsider chasing this system, even though I'm off all week. Not only is moisture a huge issue as you pointed out, but the NAM is not creating a very deep secondary surface low over western NE as the GFS had. The surface low further north has been sped up in recent runs, and on the NAM. The result is that surface winds are no longer backed in the warm sector. The 0-3km helicity values up to 800 are no more. I have about 24 hours to make a decision on this, but unless there are major changes, or Thur and into the weekend looks better, I may just sit this one out and hope there is something good to chase during my next break in late May.

 

[James Gustina]

I'm not sure whether the NAM is to be trusted on moisture right now. It scoured dews horribly on the last system and was off by a solid 7-9F. I don't think the low-60F dewpoints will make it up to Arnett/Laverne/Buffalo area but unless the cold front sitting up in Nebraska is a lot sharper than it appears at the moment, I'm not sure if moisture is going to take quite the hit that the NAM and to a lesser degree, the GFS, have progged.

 

[James Gustina]

00Z NAM has horribly mixed-out moisture, but what else is new. The kinematics still look absolutely insane for this one, with deep-layer shear hovering somewhere around 50 knots last I checked and the best upper-level dynamics look to be right in the sweetspot. At it's worst, this may end up being a nighttime event with convection firing close to sunset, with LCLs gradually lowering throughout the evening with BL cooling. I don't doubt there'll be supercells along the dryline, but the tornado threat is a little foggy considering the pretty wide margin of variance between models in overall quality of moisture during the week. I'm almost to the point of throwing out models and waiting until Tuesday night/Wednesday morning to make a solid decision.

 

[James Gustina]

That area up between Arnett/Canadian/Buffalo looks very interesting for a few big dryline storms before sunset. I doubt dews make it out of the mid-50s but the low-level wind fields are absolutely insane. 50 knot H85 winds with backed sfc winds just SW of the secondary sfc cyclone. Modest instability on the order of 1500-2000 j/kg and a broad area of diffluence overspreading the dryline in the eastern panhandle. There's also pretty high Theta-E values being progged to advect right along the edge of the dryline through Ellis/Beaver/Lipscomb/Hemphill county. I'll be stunned if there isn't robust convection somewhere in the eastern PH/northwest OK area Wednesday.

 

[Logan Karsten]

I am sitting this one out. This setup just gets worse and worse looking with every model run. With the 12Z GFS, I am seeing less than stellar shear, which makes the questionable moisture aspect much more annoying. Also, given the dews will be in the mid to upper 50s at best, I would expect relatively high LCLs. Good day for some structure shots of LPs, but definitely not a day that has me itching to go, especially with next weekend starting to look more appealing.

 

[Skip Talbot]

Moisture on the northern end of this setup, KS into NE, looks like it's "just in time." Dews are forecast to go from 45 to 60 in 9 hours. Will it actually be there? Maybe not. And then even if we do see 60F dews on the KS/NE border like the NAM is advertising, that moisture is probably going to be razor thin.

LSIs and low level instability do not look favorable for surface based storms:

Assuming you can still get some storms up with that stout capping, they'll probably be elevated. Plenty of low level instability on the cold front up in NE and the cap opens up a bit after dark up there, but again, will the moisture actually materialize up there?

SBCAPE drops off to the south and then almost completely disappears after dark.

Some discrepancies between the models on these details though, but this setup looks really iffy for anyone making a several hundred mile, one day jaunt for it. This could easily cap bust or just be a couple of striated updraft towers on the dryline at dusk. Supercellular tornado chances are meager with those LSI values, but I've seen that come around at this time frame, and it might yet given the differences between the models.

Not biting on this setup right now, but will watch for changes.

 

[Adam Atkins]

This looks like a fun hump-day chase to me! The bottom line is that if you're within 300 miles of this setup, you're probably going to venture out to the dryline and expect picturesque supercells over, arguably, the best chase terrain in the CONUS. These kinematics are beautiful for slow, rotating storms with backed low level flow, increasingly strong LLJ near sunset, and steering speeds of 25 kts.

Moisture is shallow and will arrive fairly late, but there will probably be a narrow window just before sunset with some local 60+ Tds, slightly lower surface temperatures from anvil shadowing/downdraft precip outflow to lower LCLs for a dominant right mover to produce a brief tornado. I wouldn't expect any prolific, cyclic tornado producing storms, but some gorgeous supercells are likely across Western OK and into NW Texas. The tail-end Charlie storm might have the best chance due to the higher Tds further south.

 

[Darren Addy]

After several years of doing this, I still consider myself a noob. So take this with a grain of salt (and feel free to educate me further... I'm not afraid to run my ignorance up the flagpole if it leads to me learning something).

However, it seems to me that the NAM (since it came into range) has been pretty consistent in pinpointing only one area with a chance of pre-sunset tornadoes tomorrow. That area is in extreme North Central Kansas and NE-ward into Nebraska. I'm concerned that the the area of good 0-1 EHI has been shrinking over the past several model runs, and am interested to see what the 0z run shows (and of course when the RUC comes into range in the morning). Expect a low to form in SW KS and to steal a stream of the moisture that is being drawn to what has been the dominant low in Canada. This should create a pool of moisture and a warm front near the Nebraska/Kansas border. This warm front is currently expected to lift into SE Nebraska near sundown.

Anyway, as of what I have seen over the past 24 hrs, I would be selecting the box of Franklin, NE to Red Cloud, NE to Mankato, KS to Smith Center, KS as the area I would want to be sitting. The downside to that box is that it is not the best for cell phone/data coverage, however I don't think the storms really care. It appears to me that the combination of lift and cap should hold the show off until after 5 PM. CAPE in this area is sufficiently good that even if the NAM is overshooting the moisture return there should be more than enough for storms. Bulk Shear in the area suggests supercell development.

Wishcasting: I'd like to see that box move a little farther north by go-time tomorrow. I'm not sure I can get there in time after work! Best wishes to all those heading out tomorrow.

 

[James Gustina]

The issue with tomorrow further north is that the front will probably catch up with the dryline relatively quickly and make it a hot mess express with embedded supercells. The NAM switched it's story considerably over the past two days on tomorrow which is why a blend of the GFS/ECMWF seems more believable. The far eastern PH/far western OK definitely has a shot at sunset tornadoes as the BL cools going into nighttime. The NAM seems to have grievously overestimated how badly the moisture would get wiped in western Oklahoma/TX PH. Dews rose another 5 degrees in Arnett over the past five hours and lower 50s are making their way across the Red River. The only thing really holding back tornado potential tomorrow further south will be the T/Td spreads. If 60F dews end up making it across I-40, I would bet on their being a surprise somewhere out there.

 

[Michael Thompson]

Wednesday 23 April, Target – Laverne, Oklahoma.

With the latest model runs I have pushed my target about 50-100 miles further north. This is because surface winds appear to maintaining S/SE direction much further north, with the better directional shear stretching northwards too. Earlier fears of a too linear setup northwards from central Kansas appear to be weakening, so that may be a last minute game changer. In the Oklahoma panhandle directional shear will be adequate to keep initial storms discreet. Dewpoints will be the limiting factor and I expect initial storms on the dryline to be rather elevated. Is suspect Gorilla hail is possible with one or two of the stronger supercells. Towards evening DP’s may close the gap on surface temperatures enough to lower the LCL to a possible very isolated tornado level. As Adam mentioned the storms will be very photogenic. In my opinion a much better chase prospect than a high risk day with the LCL dragging the ground, and full on gloom fest with 50mph moving storms, even if there is EF4-5.

 

[Matt Hunt]

I've chosen not to chase this one, and am waiting for the weekend instead, but if I were down there I'd target Childress, TX. That appears to be the only area along the entire dryline with the hopes of hitting 60F dewpoints late in the evening. I expect mainly high-based supercells due to the huge T/Td spreads, but with cooling around/after sunset some of the storms could become surface based and spit out a tornado or two.

 

[James Gustina]

Initial Target: Cheyenne, OK

Probably going to drift west on 40 today and see how far moisture returns north. The better overall shear environment is still progged for the NE PH/NW OK so a "somewhere in between" approach for the best storms of the day is gonna have to take that into account. These thing oughta be pretty at the very least even if the tornado threat is low. Hope everyone has good insurance too, baseballs being lofted miles outside the updraft looks like a distinct possibility.