2015-05-06 EVENT: TX/OK/KS/NE

[Jeff Duda]

This event is still 4 days out, but it has remained fairly consistent in the GFS to warrant a severe threat this coming Wednesday.

This event features a large warm sector extending as far north as possibly the Canadian border. The moist axis looks to setup near the I-35/US 81 corridor from TX through NE. Frankly I'm a little disappointed that the GFS is only progging low-mid 60s dewpoints across even the southern portion of the threat area. With this much time between FROPAs in the southern US, I hoped we'd be seeing better moisture return than this. Unfortunately the Gulf isn't really loaded right now, so I'm forced to buy those dewpoint values. Actually, a lot of the model forecasts for events in April oververified, meaning dewpoints might actually be lower than forecast.

Mid-level flow is hardly impressive. Also, the TX/OK/S KS portion appears to be just behind a shortwave trough axis moving north/northeastward out of the region at the time, so shortwave ridging may lead to spotty storm coverage in the southern portion of the region. Flow below 500 mb is pretty good, though. Looks like there will be a solid LLJ with deep moisture and no real EML, so despite some lapse rate issues in the low levels, any capping appears easily breakable if surface temps can warm to near 80. The GFS Is predicting a lot of scattered precipitation throughout the region during the day, however, so cloudiness could hold things down and make this more of a non-event.

The FIM looks to be pretty much in-line with the GFS at this point. Hopefully as the event draws near some details will change favorably.

 

[Andy Berrington]

With this much time between FROPAs in the southern US, I hoped we'd be seeing better moisture return than this. Unfortunately the Gulf isn't really loaded right now, so I'm forced to buy those dewpoint values.

That SE system (possible sub-tropical/tropical development) is what is limiting the moisture return.

 

[Stan Rose]

Should be adequate dews especially in OK. As Jeff mentioned, the models have been super consistent. What caught my eye is this is the first time this season
I recall seeing the GFS prog 50-knotters at 850, a screaming LLVL jet! I think this has all the makings of a classic dryline-triple point event, especially since I have to work so I will have to watch from the sidelines...

 

[Jeff Duda]

The event is now in range of the NAM, and the NAM shows slightly higher surface dewpoints than the GFS. Also, both the NAM and GFS are showing some pretty good 0-3 km SRH; values well over 300 m2/s2 in areas. I also see a little less early-day precipitation in the forecasts. So at least in my mind, this event looks a little more promising than it did 24 hours ago.

 

[Jeff Duda]

No longer very excited about this setup. The NAM is consistently a positive outlier among the SREF members, having more surface moisture and higher CAPE than nearly all SREF members. Also I'm seeing a trend towards lesser deep layer shear. It seems now we'll be lucky to see 35 kts and very poor storm relative flow in the midlevels. There may be a rogue supercell somewhere, but it seems at this point any discrete storms will struggle to develop or maintain supercell characteristics. Also, the magnitude of LLJ with such weak (and weakening winds) above it suggests a more linear storm mode will prevail within a few hours after convective initiation. Initial storm mode probably will not be linear given the forcing, but as cold pools coalesce and latent heating takes over, expect an MCS somewhere over KS/NE during the evening.

Saturday, on the other, hand, now has my interest. That's for another thread.

 

[Ben Holcomb]

After looking at the 00Z NAM I'm kind of meh and yay about this setup. Definitely has some potential. The NAM is probably overdoing CAPE, but the low levels still curve pretty well, but the midlevels and anvil levels are crap the further north you go - on the contrary, it seems like the lower levels curve less but you have better venting and mid level winds further south into western Oklahoma and Western North Texas. I do believe there will be a spot or two that can get it done with enough shear and instability and will probably be out to chase and may just stay out after Tuesday anyway.

Somewhere in Western Oklahoma, near perhaps Elk City is where I'd target based upon the 00Z NAM.

 

[Chip Redmond]

Definitely another day of HP mess storms with weak upper levels. As trough trends more positively tilted, ridging still increasing across Kansas on recent model trends. If only we could get the jet stream phasing timed just a little bit sooner... Subsequently though, this warming of mid-levels with ridging ahead of the next trough is continuing to increase the cap with each run. This still suggests persistent clouds across the warm sector and a less defined dryline than previous model runs. As a result, convergence may be an issue as well.

However, ensembles hint at still enough convergence to get a few isolated storms in central/south central Kansas. With decent low level veering and instability, I can't quite get myself to give up on the event just yet... Will position in south central Kansas where clouds can clear in hopes of a nice isolated supercell just before dark all to myself (hah!).

Chip

 

[Jeff Duda]

With the 00Z models coming in (haven't looked at the 00Z GFS yet, but I'll add that later), I'm a little more excited about this than I was yesterday. The NAM is still on the high side of the SREF in terms of surface moisture and CAPE, but it has been showing a little bit more deep layer shear (now some isolated areas with 40 kts across OK). The 4 km NAM has really not changed much over the past several runs - it indicates a big hole of nothing across most of OK and KS. The 00Z 4 km NAM wants to blow up a supercell near the triple point in far NC KS tomorrow afternoon. I think the lack of initiation along the dryline along such a huge stretch is due to two factors: 1) lack of decent convergence along the dryline (although the NAM wants to back the winds east of the dryline and veer them west of the dryline around 00Z tomorrow), and 2) stability due to cloud cover from convective debris from ongoing storms over TX/OK. All models have been very consistent in sliding a very large area of heavy precip across OK/TX/KS overnight and keep it going as it moves east away from the dryline. I think how tomorrow goes hinges strongly on how the current convection over TX/OK evolves. If it moves well east and/or dissipates in time for good heating to occur, I would be more confident on storms developing across OK/KS. Otherwise, I'm forced to buy the 4 km NAM's forecast of no convection across all but the fringe areas. Personally I don't feel like driving all the way to the KS-NE border.

FWIW, the 12Z NSSL WRF shows a storm (with low UH) blowing up near Watonga right at 00Z. Also the NCAR ensemble (00Z last night) blows up a few storms scattered about between NW OK and NC KS, but there's little consistency among members with that. It also shows there may be issues with convergence along the dryline as well as some possible issues with moisture mixing out a little bit ahead of the wind shift, thus loosening the moisture gradient.

The 00Z MPAS 50-3 km configuration run at MMM wants to blow up a line of cells right along I-35 over OKC tomorrow. There is some decent UH with those cells. Looks like that model places the dryline much farther east than other models discussed here. It does have some pretty decent surface dews, though (mid 60s).

Summary: as expected there is much uncertainty on the storm scale, with details depending on what happens with the mesoscale. A good day to watch the obs and sit on the dryline somewhere. Probably doesn't matter exactly where.

ADD: 00Z GFS is still noticeably different than the NAM as far as dryline placement and orientation goes. It's a little more favorable in terms of moisture quality and depth, though. The 03Z RAP is in and goes out to 21Z and seems to be more on the side of the GFS as far as dryline placement goes. The NAM is still on the high side of the SREF, but the SREF has increased moisture and instability over the last 24-48 hours. Deep layer shear still doesn't look to make it much above 35 kts, but there are some isolated spots where 40 kts could happen. The 21Z SREF is really confident about a storm blowing up near Medicine Lodge as well as some development just south of the Red River, west of Wichita Falls.

The 00Z NSSL WRF is in pretty close agreement with the 4 km NAM, which isn't too surprising since they're configured very similarly (especially with IC/LBCs). NSSL WRF says "no dice" for OK and S KS...target whatever triple point may develop.

There you have it, folks. A lot of uncertainty to go along with your information overload in this new era of NWP.

 

[Stan Rose]

Yeah, all that ongoing convection sure is making a mess of things. Both the NMM and ARW show isold-sct storms by 00Z in SW OK though. That's good enough for me (especially since I can just arm-chair quarterback from 500 miles away )
ETA: the 06 NAM is pretty gung-ho about convection near ICT 00Z on...which is where it also maximizes low level helicity. Patience may pay off.

 

[Tim Marquis]

I think the main issue isnt so much the garbage convection, its the overall subsidence left behind the exiting wave. That being said, it seems the juxtaposition of deeper moisture, strong surface heating and distance away from the jet would indicate SW OK/NW central texas would be the place to be. The 11z HRRR and RAP seem to indicate a cluster of potential supercells (based off stronger UH) to develop around 22/23z south of lawton and move east through 2z. Definitely will be something to monitor throughout the day here in OUN.

 

[Jeff Snyder]

I've been too busy to post much here lately, but, since I have a few minutes this morning, I figured I'd throw something up here. @Jeff Duda , as usual, has done an excellent job describing the model forecasts and some of the pros/cons of this setup. Morning vis sat doesn't show any widespread cirrus, which is certainly nice to see given the past few setups! With some early May sun, the low clouds should mix out later this morning and allow for decent heating ahead of the dryline. Upstream soundings at AMA and MAF show decent lapse rates aloft, though we don't look to have the deep EML we've had for some of the past setups.

12z HRRR and the 12z NAM just rolling in now are making it difficult for me to make a firm target today. The area of 40-45 kts @ 500 mb in S KS is interesting, but 250 mb flow up there is only 20-25 kts. In other words, storm-relative upper-tropospheric flow may actually be easterly today, and the "back-sheared anvil" may actually be on the east side of the updraft rather than the much more typical west side of the updraft. Very strange. KS will be in he left exit region of a moderate 250 mb jet streak, which, via the transverse circulation, should yield some ascent up there to encourage CI.

The signal for CI near the Red River between LAW and SPS remains in both the latest HRRR and NAM runs. Heck, the 12z NAM lights up a long corridor of cellular-looking convection (obviously, the low res NAM isn't modeling the convection explicitly, but the QPF field more "blobby" than linear). I haven't looked closely enough to see why CI is so far east of the dryline by a few counties, but at least there's a CI signal.

On a logistical note, parts of OK, KS, and TX have received a lot of rain in the past day or two. As such, traversing dirt roads may be very difficult today. Hopefully any local flooding will have receded by the time of CI, but there will probably be a lot of very soft dirt and gravel roads, and even the shoulders of paved roads may be soft.

 

[Jeff Duda]

but 250 mb flow up there is only 20-25 kts. In other words, storm-relative upper-tropospheric flow may actually be easterly today, and the "back-sheared anvil" may actually be on the east side of the updraft rather than the much more typical west side of the updraft. Very strange. KS will be in he left exit region of a moderate 250 mb jet streak, which, via the transverse circulation, should yield some ascent up there to encourage CI.

This is an interesting part of this setup, indeed. The difference in 250 mb flow between KS and S OK is quite stark, with the 12Z NAM and 12Z RAP progging 60-65 kts near and south of I-40 and only 20-40 kts north of the KS-NE border (the 06Z GFS is also in line with this). In fact, some model soundings from near Wichita showed flow at and above 500 mb just sitting right on the predicted SMV, meaning no storm relative flow in the upper half of the storm. This basically guarantees an HP mode if the updraft can even manage to hold all that water up (probably some weakened updrafts in the mid-upper levels of the storm). Farther south, however, there is some decent storm relative flow in the upper levels, so if a storm went up there, it may be able to hold back from going HP until later on. The moisture is better to the south, and it's likely that areas farther south will get warmer today, but perhaps one competing factor that favors the northern target a little is the degree of low-level shear this evening - about twice as strong in N OK/KS than near the Red River. Of course the 12Z NAM says there will also be increased 850 mb flow near the Red River, and even if winds only get up to 25-30 kts down south, that still makes for enough shear to get tornadoes (a good 10-20 kts of shear). I'll be keeping an eye on satellite and obs today to see where the most buoyant air develops. Hopefully it develops in an area with sufficient shear. Of course, we all know Mother Nature will do everything she can to keep the best shear separate from the best instability.

 

[Marcus Diaz]

Something about this day. I can't get myself to pull the trigger. This feels like one of those days you look back through the spc reports and see only hail and wind reports in some areas, with a random brief rain wrapped tornado report. The KS target instantly turned me off with the weak upper levels. No way I'm driving 4 hours for that. The OK target looks amazing, if it weren't for the fact that there's no forcing to fire anything off. That leaves the TX target. Looks decent, should pop storms off as seen with a sudden spot of 500mb vorticity. The shear is there for supercells and maybe a tornado. But I still don't feel like that'll be worth it. It's my gut, I guess. It's been my best forecasting tool this year, and it's telling me to stay home and wait for tomorrow. So I'll be watching this from home. And maybe something will make me eat crow. But good luck everybody else!

 

[JamesCaruso]

Actually looks like a pretty tough forecast. Although I wish I was out there, I am relieved I don't have to make any targeting decisions!

Not a lot of time to analyze today, but I would definitely want to be in extreme southern KS or western OK, along a longitude roughly along the eastern TX panhandle / OK border. I do not like the anemic 250mb winds north of the KS/OK border. The 500s don't look too good up there either. A problem is that the dryline looks to be somewhat diffuse without much convergence. 850s are southwesterly in the region noted above. Definitely prime CAPE and shear to the east, so storms that initiate should go to town once they move toward the east and northeast. Hopefully areas of greater convergence along the dryline will manifest themselves in the surface obs later today. Unfortunately, I won't have much time to look at it. Throwing a dart here but I'll say Woodward OK as an initial target.


Sent from my iPad using Tapatalk HD

 

[Andy Berrington]

High uncertainty, but potential high impact setup for western OK today. I too get the feeling that it won't pan out due to the lack of forcing, but that low level parameter space forecast by 00z is rather explosive. Would only take one supercell going up and taking a not-so-friendly track and you have a big issue. I liked the 13z outlook's assessment a lot with the suggestion of significant tornadoes, but not upgrading due to the initiation concerns. Any previous boundaries from last night's convection would likely help things.