2018-05-02 EVENT: TX/OK/KS/NE/IA/MO

Stan Rose

Mar 8, 2006
Pueblo, Colorado
Looks like a classic early May setup for the Central Plains Wednesday, with the potential for a regional severe weather outbreak.

Positive-tilted trough will be moving into the four corners region Wed morning, with a strong mid-level jet of 65-70 kts out ahead and surface development over E CO- W KS. Ongoing convection from Tuesday night will complicate the mesoscale environment, but expect recovery by midday over much of the area, and with dewpoints in the upper 60s-near 70 degrees and plenty of deep shear, the ingredients will be in place for another round of wide-scale severe by mid to late afternoon.

Greatest potential for tornadic development will likely be along the warm front in N KS, possibly S NE, with a second area of likely more isolated development along the dryline southward through OK and into N TX. SPC has this area out-looked for day 5 with a 30% risk. They even mention the possibility of a few strong tornadoes, pretty rare language for a day 5 event, but seems warranted given the expected large hodographs, particularly near the triple point and convergent zone near the dryline.

The fact that this is a day 2 event that follows closely on the heels of a decent potential day 1 in the same area makes for an attractive chase opportunity. I'm hoping the severe pain of passing three kidney stones resolves soon enough so that I'm able to be out for the event! :eek:
Agree this day looks like it holds some potential for significant severe weather.

A very large area of >65 dewpoints is forecast east of a surface low sitting in SE CO with somewhat backed surface winds east of there.
> 3,000 j/kg CAPE is forecast over S Central KS. The dry line is very evident over far western OK, then bending from SW KS to NE KS. A pretty strong upper jet should be over NM and C0

What is interesting is the NAM shows a small area of very heavy precip by 03z over mid-central KS. It is so pronounced this is what I am basing my target decision on. For now, target is Hutchison, KS.
The NAM seems to be hinting at some noticeable subsidence in the mid levels on the southern end of the dryline, which was my initial pick for a preliminary target. The Euro has appeared a bit more bullish, with the aforementioned surface low over SE Colorado and a near perfect veering profile over west central OK.

All three models(GFS, NAM, and Euro) have continued progging 2500-3000 j/kg MLCAPE ahead of the dryline and the rich moisture Mike mentioned above. I'm still mildly concerned about weird wind profiles but overall it still looks on to provide some solid chase opportunity.

One additional detail is the NAM and GFS hinting at a more substantial EML overspreading the dryline through the afternoon which should hopefully prevent an early initiation.

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I know, I know...I have a reputation for this, but then again...

I remain not particularly impressed with this setup. I definitely see widespread severe happening, but this does not look like any kind of tornado outbreak setup. In fact, it looks like anything longer than transient supercells may be hard to come by.

Up north, the front makes no northward progress during the day. In fact, based on the kinematic configuration and the separation between it and the surface low, I'd say it's basically more of a stalled cold front or a stationary front than a warm front during the day. The only place I see any substantial northward movement is well to the west where the dryline appears to shunt the boundary out of the way. But moisture quality in the panhandles and into E CO is pretty pathetic. Finally, there is a lot of alignment between the surface boundary and mid-level flow, so updrafts will tend to track along the front - strongly hinting at a quick transition to a linear storm mode along the front.

Storm mode is much more likely to be cellular to the south along the dryline. Great moisture will be in place and surface heating looks to be more than sufficient to help break the cap. I have no doubts on initiation there. However, as I pointed out in a series of tweets yesterday (https://twitter.com/wxJeffDuda/status/990656141196578816), I am concerned about the timing between initiation and maturation of the wind profiles. I noticed this in yesterday's runs, and I still see it today. The wind profile looks good by 00Z, but if storms have already been going for a few hours by then and most of the environment ahead of the dryline has been overturned, then you'll get no new storms then, and you will be dependent on existing storms to provide your show. But the wind profile at a time when initiation is more likely is pretty crappy, suggesting storms will initially be messy and may go linear or just peter out without marching into the warm sector.

Basically this configuration is reminding me of 8 May 2016 - a rather disappointing event in OK unless you like hail and left movers. I could very easily see the same thing happening here. You're going to need a storm to turn way the hell to the right.
Wednesday looks much better on 12Z guidance. DL should go well. I infer a similar scenario on both versions of the WRF, NAM and ARW. HRRR out to 36 hr is similar.

In contrast to Tuesday where I'm still looking at the TP, I like the DL better on Wednesday. Likely an outflow boundary OFB will be south of the synoptic WF on Wednesday, courtesy of Tuesday night convection. I say courtesy, because I love OFBs. Assuming the OFB verifies, I skip the WF farther north and target the OFB/DL intersection. Verbatim looks like southwest/south-central Kansas.

Little hint of a DL bulge in northwest Oklahoma as well. Such bulge would locally back low-level wind too. Ideally, for a chaser, they would all coincide. If not, a choice will be required. Choices can be stressful, but at least they cut down chaser convergence, and hopefully both work.
There has been a slight westward trend regarding today (Wednesday) and we're getting into range for some of the highest resolution convection allowing models (CAMs).

It appears that a surface low will be situated somewhere between far southeastern Colorado and the Oklahoma panhandle by this afternoon. Strong boundary layer heating should erode a capping inversion by mid-afternoon. Earlier concerns of a cap bust seem to be eroding (pun intended), but there still is a possibility that storms up in Kansas blow up quickly and lead to mergers and messy modes. It's not quite the same setup as Tuesday, so I don't expect to have Bennington 4.0.

As far as placement goes, the dryline may be as far west as the eastern portion of the Oklahoma/Texas panhandles around early afternoon. The latest suite of CAMs suggests that storms initiate, potentially explosively, in far western Oklahoma in the 20-22z time-frame. While boundary layer moisture looks a bit more favorable than the previous day, low-level shear (relatively modest) will probably be a limiting factor with respect to the tornado potential. Barring storm scale environments that could locally enhance such a threat, expect the potential for tornadic supercells to increase markedly closer to sunset. While storms in southern/central Kansas may also produce tornadoes, a tendency for a more linear mode here suggests that "chaser-friendly" tornadoes will be more likely to the south.

Into the evening, my main concern is that sufficient boundary layer moisture/instability may be maintained to sustain a tornado threat through at least part of the night. The I-35 corridor may be dodging a bullet here with the gradual westward shift, but I could still see a nighttime tornado threat reaching as far east as central Oklahoma by 02-04z. Beyond that, storm mergers and gradually increasing convective inhibition should transition any supercell tornado threat to more of a line embedded/QLCS spinup threat into the overnight/early morning hours.

Regarding Kansas convection, tendency toward an MCS appears likely by early evening. This would most likely target much of the eastern third of Kansas, eventually extending into portions of northern/western Missouri.

This is all subject to change, but confidence is increasing in the general scenarios outlined above. Convection tonight is pretty much limited to northeastern Kansas, so I don't think there will be any noteworthy effects in terms of outflow boundaries. That's a wildcard that we haven't seen yet this week.
Today is indeed a new day, with ample moisture for the dry line. Tuesday one could see the better parameters north, but CAMs looked better south. Wednesday/today is more clear in my opinion. With quality moisture, chase the dry line.

Southern Oklahoma dews have reached 70. Some of that will mix out but I figure dews can hold near 68 which is a world different than 65. Yes 3 degrees matters. Cross check down in Houston, very sticky there this morning. OUN sounding had deep enough moisture at 00Z; one has to figure 12Z is same to better. I do use Houston surface (73+ Td) as a rough check of deep moisture farther north.

Quincy correctly notes low level backing may be less than desired; so, a little mesoscale forecasting is required. Strategy is to find something to locally back those winds. I can't find a clear outflow from yesterday, but we know it's there. Might show up better mid-late morning on either VIS or surface. Boundary on DDC-ICT-Vance radar (13Z-ish) is the front, not what I'm seeking.

CAMs have a beast all by itself in west-central Oklahoma. Seems a little south compared to where I'd look for outflow. However it could be the demarcation between even deeper moisture and/or slightly backed low-levels ahead of the Panhandles upper jet. (DL bulge?) CAMs are most useful for discerning which boundary intersection to chase. CAM might not get the exact position right, but that's OK because one uses VIS and surface charts for that. Just look for the CAM's beast cell(s) on a boundary intersection.

Early morning plan would be lunch in Woodward and nowcast there. A nice park with pond and gazebo is south side of town. I will post again a more defined target here after 12Z data. By afternoon I will switch to Discord. While I'm not real clear on my boundary location attm, I look to zero in by late morning.
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The 12z OUN sounding shows a moist layer up to about 850mb. Modifying the AMA sounding for the eastern panhandle/far western Oklahoma concurs with mesoanalysis: There is already 2000-3000 J/kg of SBCAPE in place across the area. Moisture is certainly a win, but it becomes a bit more complex with the low level wind fields.

As @Jeff House said, there are no clear boundaries at the moment. High resolution guidance suggests we see surface winds start backing to SE in far southwestern Oklahoma near a dryline bulge by early afternoon. The caveat is that better backing is associated with meager low-level shear, on the order of only about 10 knots in the 0-1km layer. Farther north, into northwestern Oklahoma, southerly surface winds are still good and low-level shear is somewhat better at about 10-15 knots, based on HRRR progs.

In addition to boundary layer moisture, the other positive factor today is much better upper level support. Assuming storms stay at least semi-discrete in western Oklahoma, significant severe is quite likely.
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Plan of the Day: First target is north side of DL bulge in west-central OK. Second target is east of TP in southern Kansas. I would eat lunch in Woodward thanks to roads in six directions out of town. Keep in mind a few lights in the center of town.

DL Bulge (north side of it): 12Z CAMs are more bullish with DL convection. DL bulges in the afternoon but stops/retreats which should not be a problem. Gravity wave(s) made it into southern Oklahoma (VIS 15Z-ish); and, they count as boundaries to intersect the DL. Note after 00Z model helicity blows up in southwest OK but I believe it is feedback. I still lean toward I-40 north.

Kansas TP (just east of it): Coldwater to Medicine Lodge may offer another target. 12Z CAMs are less messy, but still a lot of cells. Keep in mind reality could over or under perform CAMs. Stationary front should stall with low press in southwest Kansas. Might be the outflow between US-54 and US-160 on VIS as I type. If so, these targets are near equals.

Conclusion: DL bulge is slightly favored today thanks to deeper moisture than on Tue. East of TP is a legit if not equal second target. Maybe spread the crowd? Safe chasing and good luck!
Reviewed the 12z CAM model runs from yesterday to see who did a good job. I think the HRRRx, WRF-ARW, and WRF-NSSL did a pretty good job. Here is a link to the HRRRx simulated reflectivity for yesterday. https://rapidrefresh.noaa.gov/hrrr/...stLen=48&fcstStrLen=-1&resizePlot=1&domain=t5

Since these guys did a relatively good job yesterday, I am going to go with persistence and say they do a good job today. They all seem to like putting a storm in SW Okla and send it off toward I-35. The HRRRx is quite problematic as it sends something toward OKC. Will these verify? I hope not, but thought it was an interesting trend. I like the DL bulge is SW Okla. I am currently compiling loops of mesonet data to see how the conditions materialize over the afternoon. If the DL pushes into Okla before 4pm I think storm could approach I35 before they get choked off. Time will tell. Good luck to all!

12z HRRRx updraft helicity

12z WRF-ARW updraft helicity
Boundaries have become obvious on Visible Satellite as of 17Z. Equal targets remain west-central OK and south-central KS.

One boundary is working north from southwest Oklahoma. If it stalls south of I-40, storms may be robust there. Previously I favored north of I-40 believing the boundary will lift. It still might. At any rate, backed winds are advecting robust moisture into western Oklahoma.

Other boundary shows up through Wichita back to Coldwater KS. The SPC refers to it as the front; I call it the outflow boundary OFB with synoptic front up toward I-70. I usually take OFB over synoptic, including today.

In both cases I would chase the boundary intersection with the dry line. Patience is required, as usual. Storm mode may get sloppy before improving with the LLJ starts. LLJ will be a little late but it'll come.
Messy forecast. Concerned about early storm coverage issues in Kansas thanks to better lift and storms already in progress at noon. Usually with high storm coverage days like this, you have 2 choices: any storm(s) interacting with boundaries, and tail-end charlie.

I am leaning on the tail-end charlie play due to a.) at the ideal spot on the progged dryline bulge, and b.) warmer H7 temps which could help keep storms more isolated. Good look to all out today.
CI showing up nicely on the 1 minute GOES visible w/ 0-3km CAPE and ML CINH overlaid. The mesoanalysis pretty much bullseyes the area of most intense convective development. Probably not too long before something substantial goes up.
Two targets has solidified IMHO. Both are boundaries exactly like Dan writes.

Storm latching onto Kansas US-160 outflow boundary. It could be low contrast until it becomes dominant. Slop risk is there, but it could also be a real long-tracker.

GOES 16 shows distinct boundary intersection in east-central Texas Panhandle. It's on the dry line bulge. One could follow that into Oklahoma. Model time is over. These targets look solid!

I am switching to Discord as nrgJeff (same picture) over there. Be safe and happy chasing!