2017-05-16 EVENT: TX/OK/KS/NE/IA/MN

[Mike Marz]

This upcoming Tuesday is closing in and it looks like a potentially solid chase day across a broad area. The NAM and GFS both show a sharp dryline setting up from parts of Nebraska down through Texas by late Tuesday afternoon. The exactly location of the dryline is still in question, but I suspect it will be somewhere in the panhandles and up through western parts of Kansas. A pretty impressive shortwave trough will be ejecting into the plains by Tuesday evening. Storms that can develop along the dryline might have an impressive environment to work with. The GFS shows a 40-45 knot 850mb LLJ straight out of the south by 00z Wednesday and backed surface flow. The forecast hodographs on the GFS look quite nice. The NAM isn't as impressive and shows more veer-back in the soundings. The thermodynamics look like they will be fine. There are possible flaws in the setup, obviously, such as LCL heights, moisture quality, ect... but either way, we will have more model runs to sift through before the event. There could also be a secondary target further north where a warm front play looks possible. This looks much more conditional at the moment. Overall, somewhere in southwest Oklahoma would be my target as of now.

 

[Jeff Duda]

As I discussed in the chat earlier today, I am concerned about capping given the rather low forecast surface temperatures east of the dryline in KS/OK. Moisture quality is also a bit lower than I would have hoped for. As of now the event certainly looks chaseable, but I see a lot of potential failure modes, including S-shaped hodographs, capping, and cloud cover further limiting destabilization. But, this may very well end up being the first true central plains dryline play of the year sadly.

 

[JeremyS]

I'm not liking the fact that the NAM shows 0 precip all along the dryline. GFS looks much better with it's precip signal but I don't know whether that's an error or issue with the GFS in instances like this. I remember back on 4/28 the models showed the same thing(NAM nothing, GFS some QPF), and the NAM was correct. Ugh, I hope this isn't another bust.

 

[Brett Roberts]

I'm not liking the fact that the NAM shows 0 precip all along the dryline. GFS looks much better with it's precip signal but I don't know whether that's an error or issue with the GFS in instances like this. I remember back on 4/28 the models showed the same thing(NAM nothing, GFS some QPF), and the NAM was correct. Ugh, I hope this isn't another bust.

I wouldn't worry too much about the QPF signal on the NAM; its convective parameterization scheme is known to have a dry bias in dryline situations like this. For example, with this past Thursday's event in SW OK, I believe it showed a cap bust in the 60-84 hr range; laughable, since the actual failure mode ended up being (partially) early initiation and messy mode. The GFS and Euro have been quite consistent in convecting along the dryline Tuesday. A cap bust is possible, but I don't think it's very likely, and the NAM has little meaningful to say about it (especially at this range).

 

[Jeremy Perez]

NAM also seems to be showing lower surface temps than GFS. I was wondering if part of the issue is how it's handling cloud cover wafting over the warm sector throughout the day...but the NAM rendering on COD has almost no nuance in its cloud cover gradients, so I can't compare easily to what GFS is seeing. Like Brett mentioned, ECMWF is happy to light up convection along the dryline, it also has that cloud cover clearing out earlier than GFS or NAM.

 

[Kevin Rider]

Moisture isn't to bad with this setup. S-shaped hodos do concern me but factoring that we are in the middle of May now and have a dryline setup for a change I have some hope. Just glancing at the 12 NAM I would draw my target radius around Buffalo, Ok. probably.

 

[Jeff Duda]

Well at least the shorter term models are now regularly convecting along the dryline in the warm sector. The NCAR ensemble was actually pretty aggressive with supercell development up and down the dryline tomorrow. I'll wishcast member #3. Still a bit disappointed in the moisture forecast given how much time has passed since the last big cold front, but flow over the Gulf remained pretty weak all weekend long, so it's probably a bit far fetched to think widespread upper 60s dews will make it to anywhere but the far southern part of the DL in time. Other aspects look okay, so I'll probably be looking to target anywhere from W OK/E TX PH through C KS as of right now. Maybe the evening models will suddenly paint a picture emphasizing one particular section of the dryline over another.

 

[RyanConnelly]

Probably goes without saying but north of the triple point is a no-go, if nothing else just based on the small critical angle. SW-NE oriented CF with SW deep layer shear vector/Bunkers Right storm motion vector ~225 deg spells immediate line-out, not to mention cold air undercutting. For tornadoes, outside of QLCS ones, that probably eliminates anything south of I-70, maybe even US-50.

Given the on-and-off NWP signal of a dryline bulge and the backed surface flow and moisture pooling that comes with it (new GFS has Dews up to 68 F in one spot!), I'd have to think Sweetwater, OK south to the Red River is the place to be.

Of course, I'm on an island that sticks out into the Atlantic Ocean, so I'll be watching from home...

 

[Dan Robinson]

Ugh - upstream moisture and trajectories in central/south Texas aren't very encouraging. Hopefully we'll see some improvement overnight, but this isn't far off from what has been indicated by the GFS and NAM in recent days:

http://weather.rap.ucar.edu/surface/sfc_abi.gif

 

[Ethan Schisler]

I can't believe its almost May 16th and we are discussing moisture lol. But yes I share the same concerns as everyone else with tomorrow. As well as some S-shaped hodographs showing up along the dry line in the Eastern TX panhandle. I have to be back Wednesday morning for an important meeting, so I'll probably sit this one out. I believe there could be a few tornadoes, but I believe the fail mode on this one is pretty high as well. So its a 50/50 shot if you ask me right now.

 

[Ethan Schisler]

Overviewing some of the 3km data that just came in. I could see a secondary play across Northern Wisconsin/Minnesota tomorrow afternoon/evening along an advancing warm front ahead of a strong surface low. The 3km NAM develops a few supercells with impressive UH tracks in this region after 21z. Its been consistent on showing this as a plausible scenario as well. Minneapolis is only a 6 hour drive for me, opposed to 12 hours to the panhandle. I may have to hedge my bet on the secondary target tomorrow since I have to be back so early on Wednesday. In addition I was looking through Space Weather and noticed a G2 watch (K6) for Tuesday night and Wednesday morning. If cloud cover isn't persistent this could give me another photography shot I've been looking for.

 

[Tim Supinie]

I'm not too worried about the moisture for tomorrow in Texas and Oklahoma. 0-1 km mean mixing ratios on the Corpus Christi and Brownsville soundings from this evening are in the 75th-90th percentile range for this time of year. Not off the charts, but very likely good enough. VADs suggest that transport of that moisture northward is ongoing. This will probably result in some cloud cover in the morning, but given that the warm/moist advection isn't that severe, I don't know that we'll have too many problems with clouds by afternoon. Residual cloud cover and stable air could limit the eastward propagation of the MCS that forms tomorrow night, but that's hardly what any of us are interested in chasing.

As for the other ingredients, the 00Z El Paso sounding shows a deep mixed layer (up to ~550 mb), and that layer has a potential temperature of ~40-41 C, which is on the low end for May EMLs. This, combined with a seasonably moist PBL should result in a breakable cap across the eastern Texas panhandle. Synoptic-scale lift should come in the form of a shortwave trough currently in the Las Vegas, NV area. The synoptic scale lift should result in lee cyclogenesis and sharpening dryline, which will provide mesoscale lift. Enhanced mixing of momentum downward to the surface on the dry side of the dryline should result in a dryline bulge setting up somewhere in the eastern TX panhandle, enhancing mesoscale convergence. Model projections indicate that shear will be more than adequate for supercells, and oriented favorably to the dryline.

If we make the 3km NAM solution a tad more pessimistic (realistic?) by increasing the temperature/dewpoint spread throughout the depth of the PBL by 4 F, the MLLCL's are still in the 1250-1300 m range; about the median for tornadoes for the Shamrock-Childress, TX area. I'd say the only two negatives are the mid- and upper-level flow that is oriented slightly southerly, which may result in upscale growth as the evening goes on. The other is that model projections have pretty consistently had some less-than-ideal storm-relative winds in the 2-4 km layer, which may result in messy storms.

 

[Kevin Rider]

I am a little concerned with the lack of cap that some models show. The early runs of the HRRR are showing many storms by 2 to 3 p.m. If too many storms go up too quickly then it could get messy and really hurt the tornado potential, at least for Kansas. You usually want that cap to hold a little longer so you can get some more isolated supercells. If storms go up too early, I think this might end up being more of a hail and wind threat. Still could get a few tornadoes early on.

 

[Ethan Schisler]

I still stuck to my guns as far as sitting this setup out last night (lol), it wasn't easy trust me after looking at the HRRR and some of the high resolution models last night. Anyway, the northern target does not look as favorable now as it did last night, so I'll probably sit this one out at home. Good luck to anyone heading out. I've got my reservations on the setup today and not just because I'm not chasing lol. I think you're best bet is going to be tail-end charlie for any tornado potential, storms further north might have issues congealing early on.

 

[Warren Faidley]

Obviously complex but far from boring forecast for today with multiple storm modes and a host of hazards. Godzilla hail may be the big story looking at the impressive capes at -20c. Lots of messy storm splits, mergers, dust storms and straight line winds. All this on top of a severe squall line later in the period. What more could you want? Likely early start time of 1-2pm of initial storms -- maybe earlier -- atmosphere already starting to brew here in AMA. Think I'll surf the dryline today without going too far east into the mess. No doubt there will be a tornado or two, even with the kinky hodo -- especially with initial cell maturity or isolated supercells. Could be an interesting secondary opportunity when OFB's move west later in the day towards dryline. Stay safe.