2015-05-08 EVENT: KS/OK/TX

[Jeff Snyder]

Well, at first glance, model forecasts show a pretty robust setup tomorrow across parts of western and central OK and adjacent areas of KS and TX. Hodographs, particularly below 700 mb, generally look quite favorable for even a significant tornado threat. I won't spend time on the "pros" for the event since they are apparent (high CAPE, strong low-level shear, adequate deep-layer shear, relatively low LCLs, etc.). So, I'll spend some time on a potential negative...

As we all know, the devil is in the details, and minor things can have major effects on a forecast. It's worth noting that the ongoing MCS in western TX northeastward into southwestern OK is putting down a lot of low theta-e outflow across far western OK and the TX panhandle right now. Temps have dropped into the mid 50s and dewpoints have fallen into the low-to-mid 50s. This may be relevant for tomorrow because, with such an expansive cold pool, it can take non-trivial amount of time to advect or vertically mix that slug of cold/dry outflow air away. I'm stating the obvious a bit here since we've had a couple of cases this year in which prior storms detrimentally modulated the severe risk anticipated for later. This may indeed happen for tomorrow's setup depending upon how long this MCS lasts. For example, 19 z temps are a good 15-20 F colder in these areas compared to the 18z forecast from this morning's NAM run. I'd have to think that this mess will continue to drift southeastward given recent radar obs, which may mean that the outflow pushes closer to central Texas. In turn, this means that the good juice will have quite a way to advect to get up into KS for the northern part of the target area. There is no synoptic push for this outflow at least (the "background" low-level flow is southerly or southeasterly), but it's entirely unknown how far south this outflow will get today.

I don't think this will have a major impact since we're 24+ hours before the event and the LLJ should be pretty strong tonight. You never know, though. The 12z 4 km NAM is too far north with this ongoing activity as it is. *If* outflow from today's activity doesn't affect the low-level thermo tomorrow, then we could see a potential severe weather outbreak across the area.

 

[silverken]

I find it interesting that there is a sudden appearance of a moisture bubble in the OK panhandle on the 700 mb NAM @ 21z tomorrow. Nearly identical location to the one that appeared on 5/4/07 @ 00z.

 

[Ben Holcomb]

Definitely a lot to like about tomorrow - 12Z Soundings show much steeper lapse rates out west than the past few days, even Flagstaff wasn't bad. I can understand your concern Jeff, but on the flip side it also seems like we're going to get all this crap out of here early today, and keep mid 60 dewpoints to lower 70's just south of the I-20 corridor. I can't imagine the OFB would surge way south, especially after all the crap we had in OK last night - look at the recovery we had (Currently 72-75 over mid/upper 60 dews in Central OK)

While the LLJ doesn't look particularly strong, and we don't really start developing a sfc low up in the TX PH until later in the day (according to NAM) I would still think it's reasonable to see low to mid 60 dews in western Oklahoma and eastern Texas Panhandle tomorrow. What I am worried about is mid level flow if you just look at the 12Z NAM - It's showing the sub tropical jet remnants that we have hitting the target area early in the day, which would lead me to believe we'll have some forcing for ascent early in the day. I would hate to see things go up early tomorrow as I don't think everything will be in place with a decaying jet before the main trough impacts the area around dark.

If we don't have too much garbage earlier, I could seriously see a significant after dark scenario. The forecast soundings and hodos tomorrow are nuts after 00Z with almost 200 m2/s2 0-1 SRH up near the KS/OK border.

 

[Jeff Duda]

Very good points, Jeff. A subsequent thought (just my old man brain at work): what if this MCS/convective cluster takes so long evolving (and persists well into the overnight given the moisture in place and southerly flow in the low levels) that it persists long enough to prohibit early initiation tomorrow, but not prohibit initiation later in the day? Obviously it would take a lot of things to go just right in order for that to happen, but I'm just stating a possible scenario in which the current convection could turn out to ultimately favor a decent event tomorrow.

Damn mesoscale...

 

[Brian McKibben]

Friday has some intrigue for the OKC metro 4km NAM shows the WF setting up along the I-40 corridor. The warm sector looks robust. SBCape in the ~4000 j/kg range. If storm latches onto that boundary and pushes east it could have some maximized helicity. Once again I will be storm chasing from my shelter door in Moore. Good luck to all!

 

[Andy Berrington]

Looks as though some of the preliminary high resolution guidance wants to fire off an MCS in E NM tomorrow morning and track it through the highest risk area, which could put a big damper on the threat. Obviously going to be a wake up and see situation.

 

[Jared Orr]

One encouraging thing I see is a blip of elevated convection already in Texas right now. This should grow and overspread SW OK for the rest of the morning...maybe if we can get this s%&t over with before peak heating, the air-mass will have time to recover quickly enough for a second initiation around 6-7...I've been bit already this year with storms forming in a very favorable area on paper and then dying because they are now dealing with weaker lapse rates and disturbed air. This is a tough call today, whether I should go or not.

 

[Marcus Diaz]

So I'm up early to check out some things. First off, I noticed the 6z NAM is still pointing towards a big day. And I can see why. Last night's MCS didn't really hamper the moisture too much. I'm seeing 70 dews in the DFW area and mid 60s along I-20 westward towards MAF. This means our source region is relatively untouched. Also, 6z NAM shows the early precip does fire into the TX Panhandle, but it shoves it NE into central OK. But with strong WAA, it looks like the dryline will have time to recover. The CAPE is dead over central OK at 0z, but ultimately that might be a good thing for the poor folks in the OKC metro. If this scenario can play out correctly, the precip should clear out in time for the area on and just east of the dryline to recover. This area in the eastern TX Panhandle and subsequent western OK is still in a nicely sheared environment. So as long as the precip clears out and we get some sun to bake the area, the day should be saved.

The worst case scenario is this early precip fires farther south. This effectively will cut off the better sheared environment from the moisture. Not to mention surface temps will tank and we'll never get the instability there. This setup has spectacular written all over it. But the fat lady might be waking up early to sing us the song of her people...

EDIT - Jared, it appears the elevated precip is firing off an outflow boundary. I think the main storms we're concerned with won't show their ugly faces until mid-morning. But you're right, I'd rather see this stuff fire earlier and more north to get the recovery going much faster.

 

[Jared Orr]

EDIT - Jared, it appears the elevated precip is firing off an outflow boundary. I think the main storms we're concerned with won't show their ugly faces until mid-morning. But you're right, I'd rather see this stuff fire earlier and more north to get the recovery going much faster.

Thanks Marcus...That outflow boundary is also reinforcing the warm front on the RAP isn't it? I was wondering why the RAP didn't show the warm front surging as far north as the NAM...it could be old outflow as well as the fact that the RAP has more backed sfc winds due to a supplemental surface low that does not show up on the NAM. Extra backed sfc winds could prevent the front from surging north. Which one of these is more likely, or is it something else?

 

[Marcus Diaz]

Yeah, I'm curious as to why the RAP isn't lifting/diffusing the OFB if its not even breaking any precip out. RAP has bust written all over it unless you go way south into Central TX. Not sure I buy the RAP though since it failed badly the last couple of days. Regardless, the RAP is still painting a pretty picture down south as the shear looks good. The 850s aren't as strong on any target. But if this convection is robust and doesn't clear out in time, better be ready for a chase in the TX Hill Country (bad terrain and road network).

 

[Zack Hargrove]

Models all seem to be in agreement that there will be two rounds of storms. This initial elevated convection should really get going by 18-20z and quickly move north and east. As we get towards afternoon, some of this may become surface based into central and eastern OK, but the real threat will be the secondary convection that fires on the dryline. All of the models (with the exception of the bizarre RAP solution) paint a picture that the atmosphere will recover in plenty of time with an impressive parameter space by 21-00z in the eastern TX panhandle and into western OK. The NAM brings the initial piece of shortwave energy into the area around 18-20z which seems to coincide with the development of the initial convection. There will be a brief break in the mid-level flow before the next wave enters around 00-03. I believe some small scale subsidence in between the two waves is what is helping to break up the clouds and letting the atmosphere recover by late afternoon and evening. Because of the modest cap and the nature of the forcing, I would not be surprised at all if we end up having a decent nocturnal tornado event, especially with that low level jet really kicking in by 03z. Let's just hope that initial surge of mid-level flow doesn't ruin the day.

If I were chasing today, and oh how I wish I were... I'd target Childress, TX and east. The biggest challenge for me would be whether to stay north or south of the river. However, the parameter space is a bit more impressive north or the river right now.

 

[Marcus Diaz]

10z run of the HRRR showing a good scenario. Yes, precip still firing at 11am in the eastern Panhandle. This rolls through OK and looks like there's some high embedded UH numbers near and north of I-40 in the early afternoon. More precip fires south of the Red River a couple of hours later, and looks rather strong as well. Then, later in the evening it shows stuff firing off the dryline in the panhandle. This definitely leaves everyone with options.

 

[Marcus Diaz]

Tornado watch just went up for west Texas until 5 pm. Some elevated supercells are ongoing between Clovis and Lubbock. These should continue east and once we get sufficient heating, should become surface based.

 

[Chip Redmond]

Really wish we could speed up this MCS crap and get an actual glimpse of warm front position/atmosphere potential in the wake of it. I also see the potential with substantial shear today-that the MCS could quasi-break up into more of an isolated threat over central OK. That is, if the outflow boundary/warm front can move that for north. One would think that as low deepens to the west as a result of the strengthening 500mb jet, that it wouldn't take too much to push it north into OK, but any MCS that forms can erase that poleward propagation quickly.

The secondary target along the High Plains is tempting too. It produced a few storms before the subsidence knocked them out yesterday. With stronger flow it should be harder for subsidence to hamper convection, and if the MCS doesn't materialize, this area could be a great shot at a landspout or two from a dominant supercell.

Will drift SW and see what mother nature provides...

Chip

 

[Zack Hargrove]

Radar trends when compared with hi res models do not lend much confidence... not liking the way things are trending.