2015-05-16 EVENT: TX, OK, KS, NE, SD, IA, MO,MN

[Jeff House]

18Z high-res NAM is slightly better than the 12Z for chasing purposes, but we are still well beyond the 36-48 hr improvement. 18Z (Thu) NAM for Saturday has morning/midday rain ejecting east off the target ever so slightly faster. More importantly the LLJ strengthens nicely and is backed slightly from straight south. The 925 mb (I know too early) shows better inflow into sups. 12Z had no good inflow; just hailers. Upstairs has not changed much for 500-200 mb. If straight hodos one would probably just target slightly deeper into the backed 850/925 winds than the usual right on the boundary thinking. Saturday pattern still looks good.

 

[Logan Karsten]

Saturday to me screams bust potential with similar problems as last Saturday.

The GFS has, and continues to develop convection over a large chunk of western Texas Friday night into Saturday morning, hampering recovery across the warm sector significantly. Granted, the high-res NAM is aggressively trying to paint a good dryline play across Oklahoma, I am hesitant to buy into that given the GFS solutions. These are the same problems that plagued the southern plains last weekend, and I see the same problems for this setup.

 

[Dean Baron]

I am keeping an eye on a potential sleeper target along the warm front in southeastern ND. 4km NAM shows temps warming to about 80 contributing to decent instability in the 2000-3000 range. Helicities seem to be a bit offset from the instabilty but the 4km NAM still breaks out storms in the 21z-0z timeframe. Could be an interesting secondary/closer target than going south for me. I just don't see a whole lot of hope right now to warrant a big drive to NE/KS.

 

[Matt Hunt]

I'm beginning to gain a little more confidence in Saturday. The NAM4KM seems to be lightening up on the early convection, particularly at the southern end of it, clearing out SW Oklahoma by late morning/early afternoon. Unlike last Saturday, there's actually a decent low level jet which should aid in bringing moisture back in. I think the NAM4KM is probably overdoing the CAPE, but the NAM is showing 2000-2500 in SW OK. Hodographs look a bit better down in this region as well, as upper-level winds don't veer quite as much as they do further north. There are still the concerns with what actually happens with the early convection, and I'm also concerned with how much convergence there will be with an ill-defined dryline and surface winds that merge a little more than converge, if that makes any sense. It's about a 14 hour drive for me, so I'm still pretty hesitant, but will likely make a final decision after tomorrow's 12z runs.

 

[James Gustina]

The spread on the SREF is not making me feel good about the accuracy of forecasting this event right now. Last NAM run had terrible, unidirectional shear profiles and meh instability across NW OK/S KS with the better veering over SW OK. I doubt moisture ends being an issue but a washed out dryline seems to be a huge concern. GFS breaks a metric ton of precip throughout the day further west and as Jeff and other noted, the MPAS shows a decently different scenario. Looks like a morning-of forecast yet again.

 

[Russ Conlon]

First off, thanks to Jeff Duda for the MPAS link. Question, is this model an experimental mid-range derivative of the NAM combined with the hourly forecast projection of the HRRR? Second, looking at this model it seems to give a clue to these some curious precip breakout patterns I have seen with the NAM the last couple of days regarding this day. I was trying to figure out why the early morning convection was dissipating between 15-21z as it crawled eastward out of eastern NM across the panhandle as the day went on and then suddenly there is a big blowup of precip along I-35 at 00z.

Food for thought: I'm seeing that 500 MB come in, dig itself in, and impressive intensification of wind speed between 12-18Z on MPAS. It looks like the MPAS is forecasting that smoking 500 MB jet to shear apart that convection and leave the area east of Highway 81 in Oklahoma untouched, seeing CAPE values increase to 2000-3500 SBCAPE with temps breaching 80 degrees by 22Z. Dryline is progged to make its move out of the NM/TX border and be around Highway 183 at 00Z. On a side note, surface to 500 MB crossover on NAM at 00Z looks incredible over central Oklahoma. Heck, it's just one model and banking on just MPAS would put me in wishcasting torment. However, this scenario is entirely plausible and shouldn't be discounted. I'd keep an eye on central and NE Oklahoma and south central and southeast Kansas on future model runs in the next 36 hours.

 

[Andy Berrington]

The spread on the SREF is not making me feel good about the accuracy of forecasting this event right now. Last NAM run had terrible, unidirectional shear profiles and meh instability across NW OK/S KS with the better veering over SW OK. I doubt moisture ends being an issue but a washed out dryline seems to be a huge concern. GFS breaks a metric ton of precip throughout the day further west and as Jeff and other noted, the MPAS shows a decently different scenario. Looks like a morning-of forecast yet again.

Yeah it's kind of funny. The 00z NAM appears to have increased the instability for Saturday across much of the threat area while the GFS decreased it. I'm still not buying the GFS' low level shear given the magnitude of this system and its wind fields, for one. It has had problems with this all year.

 

[Brandon Clement]

The 4k is looking incredible for tomorrow across central Ks. Only problem is the Nam and GFS look marginal at best. The difference between the models is the 4k clears out crapvection by mid morning then noses the LLJ in by mid afternoon. The Nam and GFS never really clear out and the LLJ doesn't nose in until dark. The difference is rather extreme. If the 4k verifies both in terms of parameters and simulated radar there will be a lot of tornadoes in central Ks tomorrow with the potential for multiple violent tornadoes. If the Nam or GFS verify it will result in chaser tears. Been debating on making the 12 hour drive but not with the current model spread. As amazed as I am with the accuracy of the 4k and hrrr on some days and astonished just how far the hires models have come over the last decade I'm equally as perplexed to how poorly all the models seem to forecast eml strengths. When they don't get the cap right the models perform horribly and none of the models have been consistent this year. Pretty sure tomorrow the visible satellite will tell everything we need to know about 11am. I'm also equally as sure the questions will linger until then.

 

[Jeff Duda]

I don't think there's too much left to be said for this event. The various models have remained fairly consistent among their own prior runs, although there are still some big differences between models on how things will evolve.

All flavors of the NAM remain bullish on lesser overnight/morning convection across the TX PH and OK and significant recovery and destabilization in time for high to extreme instability to setup just ahead of the dryline, firing storms off across W OK and into SW KS anywhere between 18Z and 00Z. If the NAM forecasts verify, I'd say we'd be looking at a solid MDT outbreak.

The GFS maintains widespread and persistent convection across the entire southern half of the target area throughout the day and has substantially lower CAPE. While it contains significant precip coverage, one would have to believe the precip it is plotting would either be not cellular or not strong enough to pose a significant severe weather threat. The FIM graphics page doesn't offer quite as good of details as the other models, but it is closer to the GFS solution, although it seems to think storms will form well east of the DL. In fact, it progs precip on or east of I-35 by 00Z, somewhat removed from the better shear.

The NCAR ensemble I've been looking at lately is split pretty good. 6 or 7 of the members develop discrete storms somewhere across W/C OK or SW KS between 18Z and 00Z although in varying locations and coverage. Two or three more members develop embedded intense storms within early day convection, but with room to the south for undiluted inflow. Another member is messy and tries to blow up a big line of embedded cells.

The most recent MPAS forecast looks pretty similar to the previous one, although it may have backed off somewhat on the coverage. However, it still progs several rotating storms mainly within about 50 miles of the I-35 corridor across S KS and OK. As @Brett Roberts had commented earlier, the MPAS may have a tendency to put things too far east. That gives me some piece of mind seeing as it still wants to bring a high-UH track right across the OKC metro area tomorrow afternoon. Let's hope that ends up happening 100 miles to the west.

This event will be much last last Saturday's event - wait and see. It all depends on how widespread and persistent the overnight convection ends up being. If it moves through quickly and leaves little cloud debris in its wake, game on. Otherwise, it'll probably be another junkfest.

Of course, I've ignored W KS and E CO throughout this discussion. The NCAR ensemble does blow up discrete storms near the CO-KS border, too. So that might be another good place to play.

 

[Jeff Duda]

FWIW, my recollection of earlier NAM and GFS forecasts this week of the 00Z dryline position for Friday (other forecast thread, but valid about 2 hours ago) verified a bit farther west than the 72ish hour forecasts. So the system may be slowing down or the models just mixed the moisture out too fast/too far east. Perhaps this means the DL will situate a bit further west tomorrow than the models had been predicting. I think they have been fairly accurate once it gets down to < 48 hrs.

 

[Brian McKibben]

00z runs are in... My thoughts regarding W/C and SW Oklahoma into the OKC Metro.

HRRR - Particularly worrisome (from a general public standpoint) with this one is that the precip doesn't look to work over the atmosphere too much tonight. Early morning precip begins to vaporize starting around 12z. And then mid morning (15z) it is already showing SBCAPE >2000. One can only imagine that number will climb as we get some sun and heating. Surface temps across SW Oklahoma are already in the mid to upper 70s by 15z.

RAP - SBCAPE >2500 by 18z and STP creaping up past 2. Not sure what to make of the morning convection with the RAP.

NAM - At 00z the NAM has a line of storms along Hwy-81 corridor at 00z, Tds ~ 70° F, SBCAPE 2500+, MLCAPE 1500-2500, STP approaching 4 in OKC Metro and 5 along DL. 250 hPa @ 110 kt over NM, 500 hPa speed max over SW Oklahoma @ 80 kt.

4km NAM - Brings convection over SW Oklahoma in the morning. Develops Storms along DL in East TX panhandle between 19-20z. Potentially a few warm sector storms along I-44 corridor possibly from morning outflow. Storms approach OKC metro by 01z (8pm). SBCAPE ~4000 at 22z. UH shows warm sector storm going over OKC at 00z and several other DL supercells approaching Hwy-81 corridor at 00z as well.

MPAS - I'll leave that up to our resident MPAS met Jeff Duda Thanks buddy!

If we wake up and see the radar looking better than last Saturday then we could be in for a long day.

Target: My upstairs window looking west and storm shelter in Moore. Good luck to all. If i could chase I would head west on I-40 and then decide whether to go North or South once the 12z runs come in.

 

[Eddie O'Neal]

00z runs are in... My thoughts regarding W/C and SW Oklahoma into the OKC Metro.

HRRR - Particularly worrisome (from a general public standpoint) with this one is that the precip doesn't look to work over the atmosphere too much tonight. Early morning precip begins to vaporize starting around 12z. And then mid morning (15z) it is already showing SBCAPE >2000. One can only imagine that number will climb as we get some sun and heating. Surface temps across SW Oklahoma are already in the mid to upper 70s by 15z.

RAP - SBCAPE >2500 by 18z and STP creaping up past 2. Not sure what to make of the morning convection with the RAP.

NAM - At 00z the NAM has a line of storms along Hwy-81 corridor at 00z, Tds ~ 70° F, SBCAPE 2500+, MLCAPE 1500-2500, STP approaching 4 in OKC Metro and 5 along DL. 250 hPa @ 110 kt over NM, 500 hPa speed max over SW Oklahoma @ 80 kt.

4km NAM - Brings convection over SW Oklahoma in the morning. Develops Storms along DL in East TX panhandle between 19-20z. Potentially a few warm sector storms along I-44 corridor possibly from morning outflow. Storms approach OKC metro by 01z (8pm). SBCAPE ~4000 at 22z. UH shows warm sector storm going over OKC at 00z and several other DL supercells approaching Hwy-81 corridor at 00z as well.

MPAS - I'll leave that up to our resident MPAS met Jeff Duda Thanks buddy!

If we wake up and see the radar looking better than last Saturday then we could be in for a long day.

Target: My upstairs window looking west and storm shelter in Moore. Good luck to all. If i could chase I would head west on I-40 and then decide whether to go North or South once the 12z runs come in.

Brian,

I agree. I am sitting here with my chase partner looking over the new models. I definitely have some concerns for the OKC metro area. If I look out my bedroom window mid-morning and see sunshine I feel like we are in for one heck of a day around here. I personally would like to chase a little further north tomorrow, but for now all we can do is wait and see. By the way this is my first post since becoming a member. I am very excited to learn and share with you all.


Edgar

 

[Brandon Clement]

It's going to take more than sunshine because early sunshine just means storms will fire fairly early. The higher 700mb temps to the south will need to push a bit farther north. But yes, big concern for the OKC metro, areas along the red river and even the DFW metro.

Not sure if this is the right place or not so I apoligize in advance if it is not.
Everyone chasing tomorrow please be very aware of flooding. Do not put yourself in a situation where you could get caught between a flooded road and a tornado. Sounds silly and simple but in the heat of the moment it's easy to forget.

 

[Andy Wade]

Out west, attempts at upscale growth into small line segments have floundered for the moment and disorganized, mostly sub-severe clusters dominate.

The trend in short-term guidance seems to be up. HRRR in particular does stand out as concerning. I don't want to punch my hype train ticket with so much unwanted convection still ongoing, but should widespread 3000+ J/kg SBCAPE at 18z verify, nobody here needs me to tell them that's a big day.

I see a couple possible complications, if a severe weather event does unfold...

- Open warm sector initiation. Little to no capping, synoptic forcing for ascent, and likely some remnant outflow boundaries would set the stage for convection to initiate away from the dryline/front. Multiple CAMs insist on it.

- Significant nocturnal tornadoes. There's not much room for quick PBL stabilization with deep rich moisture, relatively low T-Td spreads, and absence of the warm 850s that would accompany a stout EML. I've seen a whole lot of 03z forecast soundings that are basically moist adiabatic in the lowest levels with negligible CIN. One caveat--upscale growth could remove the supercell tornado risk by that time.

 

[Kelton Halbert]

The full 5 day run of the 3km CONUS MPAS (Model for Prediction Across Scales) isn't finished yet and won't be until morning (and therefore plots unavailable until after), but the first 24 hours are in so I went ahead and generated some of the output. This is 1km AGL reflectivity with hourly max UH tracks. I had made this for my friend Jamie, so I made sure to annotate the max UH tracks so he knows where to go .

Looks like Central OK is in for a rough day.