2016-04-26 EVENT: TX/OK/KS

[Ben Holcomb]

We're officially 1 day within the range of the NAM. The 12Z GFS still maintains a very ominous day in Central Oklahoma into Southern Kansas with not much wavering on the timing or degree of instability. What a time to be chasing!

 

[Jason McKittrick]

A quick comparison between the 00z GFS and the 12z GFS, it looks like the 500mb wind max is slightly slower ejecting into the southern plains. If this trend continues it may help to move the target area a little further west into slightly better chase territory. Fingers crossed.

 

[Taylor Wright]

A quick comparison between the 00z GFS and the 12z GFS, it looks like the 500mb wind max is slightly slower ejecting into the southern plains. If this trend continues it may help to move the target area a little further west into slightly better chase territory. Fingers crossed.

Let's hope the dryline follows suit and moves west, as it usually does. Not a fan of all the forcing being 100 miles west of the good moisture and instability. Also, late arrival of the jet could mean cap bust. Hoping for the western solution with a slightly faster ejecting speed max. Although eastward extent of dryline mixing is an aforementioned issue with the GFS, it appears to be evident on the ECMWF as well, putting the dryline well east of I-35. I'm hoping 850s can back a bit more to reduce the eastward extent of mixing. I noticed it deepened the 850 mb low a bit on the 12z run, which could help.

Fingers crossed, but not getting my hopes too high as there are still some issues to be resolved with this. Liking the Enid area but the warm front in central Kansas could be a decent target too with the insane-o shear. Give it a day or two and we should really have an idea as to the magnitude of this event.

 

[Jason McKittrick]

6z NAM even slower with ejecting jet max. However it still appears moderate flow will overspread the dry line by midday. I am liking central Kansas more and more as the event gets closer. Good cross boundary flow, and proximity to stronger wind fields will support discrete storm mode. Great surface convergence combined with slightly shallower lapse rates will aid in sufficiently early initiation and backed surface winds will provide necessary low level shear. Only draw back is the anticipated northeasterly storm motion and the relatively narrow warm sector. That might be enough to push me to a more southern target.


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[JamesCaruso]

00Z GFS looks great. Dryline seems in a good location west of I-35. If I could be out there, it would be a tough choice between the KS warm front play and the OK dryline play. I would probably be inclined toward the southern target due to better CAPE and orientation of the mid level flow relative to the dryline. Northern target should have better low-level backing/shear but mid level winds are slightly more meridional there. Then again, a desire to avoid the OKC area might be enough to make me move north. All a moot fantasy for me out here in Philadelphia

Noted that the 06Z GFS seems to push the warm front further north but it also seems somewhat more diffuse. Also less convergence along the dryline and dryline looks a bit further east. I am used to ignoring the off-hour runs but my understanding is maybe I shouldn't because they have improved??

 

[Warren Faidley]

There has been a model trend (including the 06Z NAM) to slow down this system and detach the best shear from the DL until after 00Z, e.g., >darkness. Not sure if that trend will continue or if the northern target will have a slightly better chance with timing. 12Z NAM should be out any minute to see if trend continues.

 

[Mike Marz]

As Warren just mentioned, it does appear that the trend is continuing with the 12z NAM to keep the best upper level flow west of the dryline at 00z. BUT, if the models are over mixing the dryline and she can hang back a bit in western Kansas, that would be excellent. I still think much will change. Also of note on this 12z NAM run is the stronger 850s at 00z are displaced well east in the warm sector, which is not good. But like I said, it will obviously all change again. One thing that should be good from a chasing perspective is that it doesn't look like an obvious target, and chasers should be relatively spread out. That TP, wherever it sets up, is also a very interesting target, if not the primary target.

 

[Trey Thee]

As Warren just mentioned, it does appear that the trend is continuing with the 12z NAM to keep the best upper level flow west of the dryline at 00z. BUT, if the models are over mixing the dryline and she can hang back a bit in western Kansas, that would be excellent. I still think much will change. Also of note on this 12z NAM run is the stronger 850s at 00z are displaced well east in the warm sector, which is not good. But like I said, it will obviously all change again. One thing that should be good from a chasing perspective is that it doesn't look like an obvious target, and chasers should be relatively spread out. That TP, wherever it sets up, is also a very interesting target, if not the primary target.

Making the triple point all the more appealing. Windfields concern me just because I've seen systems bust due to placement differences like this.
If I had a choice or the time to chase anywhere on this setup, right now I'd be heading toward west central kansas. I'm wondering if we'll see the NAM push a few features east once the system is fully sampled.

 

[Mike Marz]

Just based on past observations, and seeing what actually happens the day of an event when compared to the models this far out, I'd still bank on the TP being near DDC or just east of there around 00z, and the dryline mixing to about 30-40 miles west of OKC by 00z. If the upper level energy is timed right and the 850s come back in line, as they do with today's 12z GFS run (funny, since when are we liking the GFS over the NAM at this range) I am still hopeful for a solid dryline play. Just from a chasing perspective, I am hoping I don't have to go after the TP/WF.

 

[Randall Bragg]

As mentioned above, there are similarities to the May 3rd, 1999 event. My chase partner from that day and I are going to do exactly what we did 17 years ago, head to Chickasha and follow any super cell that forms in that area. Right to the Newcastle, Bridge Creek, and Moore, OK route. I know we are 3 days out and things will change, but if the data stays like it is now, that's our target area.

 

[Jeff Duda]

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[Jeff Duda]

I'm gonna go on the record and say the way things are trending, I don't see this being a big event. Still a setup well worth chasing, but no outbreak.

I was expecting to see the 12Z NAM come in and plaster the dryline region in W OK/C KS with the high moisture that the GFS was, for some reason, cutting out in several previous runs. Instead I see the NAM prog a more neutrally tilted and westward placed trough axis well over C CO at 00Z with the eastern edge of the "acceptable" (defined here as 40 kts or larger) 500 mb flow just barely into W OK with a nose covering most of W KS. One might think, fine, we'll just accept somewhat lesser shear right along the dryline; at least the moisture will be there (unlike what the GFS had been saying). Nope, the NAM has rather shallow moisture, and only a very limited axis above the surface. I also see some capping concerns. It looks very likely there will be an EML in place over the central and southern Plains which is great for getting extreme instability (assuming the moisture is there), but there is a bit of a capping inversion. It does appear surface winds will be backed enough to provide some pretty solid convergence, so I don't think the cap will prevail, but the lack of signal in the precip and mid-level temperature fields in the 12Z NAM is kind of telling.

Also, the difference on the synoptic scale between the NAM and GFS this far out does not offer high hopes in terms of certainty of this event. The GFS puts the trough noticeably farther east, but also continues to take a huge chunk out of the moisture along the dryline just off the surface. I have been suspecting since Wednesday that this was the result of inadequacies in the GFS' PBL physics scheme. Seeing the 12Z NAM makes me think I'm right, but again, the 12Z NAM didn't restore what the GFS removed.

Finally, the 15Z SREF does not prog an outbreak either. It struggles to maintain mid-60s dews east of the dryline, and suggests 500 mb flow collapsing as the day wears on such that shear will end up only being adequate rather than extraordinary. Low-level shear also doesn't appear to be incredible, but again, adequate for tornadoes. It has a precip signal, but it doesn't suggest the ingredients for sig tors are highly likely to align, at least for a long time.

Given the current weather on this Saturday afternoon, I'm tending to think this toned down forecast may be accurate. The main reason is looking at moisture and wind over the Gulf. A ridge remains in place over the northwestern Gulf, basically continuing to restrict moisture return. The only onshore flow right now is in deep south Texas and northern Mexico, where it also was yesterday. Also, it's not like the Gulf is completely loaded either. There aren't even 60s dews right at the coast in most places. I know this is still 3.5 days away, and there is an intervening trough to get past, but this evolution makes me want to think the more conservative forecast of moisture quality will verify.

 

[Stan Rose]

As Jeff mentioned, timing differences are disconcerting but the 00Z NAM is holding tight with its more western solution. Surface winds seem to have some better backing too in the latest run--I suspect lack of llvl shear will not be an issue, and there's a boatload of bulk shear and more than adequate CAPE. Would like to see the low centers a bit farther south--am somewhat skeptical of the moisture quality that far north--and therefore a lack of negative tilt in the trough, but overall, looking at the big picture I could see a regional outbreak coming out of this setup.

 

[Joe Pudlik]

Regarding the NAM, and some other guidance, the VBV profiles showing up are a bit of a concern as well.

 

[Greg Blumberg]

Agreeing with Jeff et al. regarding the wind profile. The key is to look at the ensembles to highlight any uncertainty with respect to this forecast. Ensembles may help with not just the storm scale/mesoscale forecast, but also the synoptic scale forecast. For example, the two key synoptic scale ensembles (NAEFS and SREF) are indicating that there are timing issues associated with the shortwave trough that is progged to be the source of enhanced lift and shear for Tuesday's event. Some members have the 500 mb flow a little more meridional than some of us would like (see attached SREF map), which is contributing to the cold advection between 500-700 mb and veer/back/veer wind profile (see attached SREF sounding). Such a profile can rob you of better storm-relative helicity or create an environment with strong synoptic scale lift and a wind pattern that is more conducive to more storm coverage rather than discrete cells. Contrary to the hype this event has brought forth, this forecast (like many of at this lead time) is not locked in solid for a significant tornado outbreak, although current public forecasts are more than justified for highlighting the potential for severe weather. Many of the ingredients are present for such an event, but there are always failure modes for events like these.