2012-04-12 FCST: KS/OK/TX

[Tim Supinie]

Alright, I'll bite.

This morning's 12Z GFS and ECMWF have pretty good agreement on a jet streak nosing into the southern Plains on Thursday, April 12. This would be accompanied by the usual requirements for a chaseable setup: decent moisture return, a sharp dryline, and wind shear. So I have some confidence in starting to "officially" watch the day.

Pro's for the setup:

1. Shear (mostly). Directional shear is excellent, with ~90 degrees of turning between the surface and 500 mb. 0-6 km bulk shear is 40-50 kts, which is good enough. Forecast soundings from northwest OK show relatively large hodographs.

Here are some things that I'll be watching for as the day gets nearer:

1. Capping. The GFS keeps the surface layer cool relative to 850 mb, possibly because of cloud cover in the model, which is not incredibly skillful in a 40-km model. Anyway, it's something to watch to see if it gets worse with later runs.
2. Moisture quality. The surface moisture trajectories aren't the greatest I've seen (they originate from approximately Florida), but hopefully it won't be an issue with the boundary layer mixing too much. Moisture at the 850 mb level originates from approximately the Bay of Campeche. Also, it remains to be seen whether the GFS will over-forecast the magnitude of moisture. Looks like we have a modified continental polar air mass over the northern part of the Gulf now, so we'll have to get that out of here. Hopefully, we won't end up with one of those days where the good quality moisture can't quite get up here in time.
3. Speed shear. The 300-mb winds are barely breaking 50 knots near the KS/OK border north of Woodward. This means that any slow-down with the jet streak could pose issues with low speed shear and and forcing. The upside to this is that anything that forms won't be moving at warp speed.

Also, this may turn out to be the first day of a multi-day event, so this may be a sort of "day-before-the-day" setup. If it pans out, I would be sorely tempted to chase this setup, but actually going would depend on the amount of research that gets done between now and Thursday and the appeal of the possible later setups (potentially on a weekend).

 

[Marcus Diaz]

I'm liking this day a lot, maybe because its fairly close to me, or maybe its because the models are painting a pretty picture. The dryline is setting up from west TX, up through the panhandle, all the way up through Kansas, Nebraska, and the Dakotas. With 60 dews progged right up on the dryline. The moisture will have a couple of days to pool against the dryline around southern KS, and through the panhandles. Widespread bulk shear of 40-50kt seems to be in order across the area. The LLJ will be a stout 40-50kt southerly jet from the panhandle - north. The CAPE axis is a touch worrying, with only a sliver of 1500 MLCAPE in order for the panhandles. The other worry is the stout EML over the area. Reguardless, the GFS has been consistently breaking precip along the dryline for several runs, so I'm confident capping won't be an issue.

All in all, this is a classic southern plains setup. One of those days where all you have to do is chase smart, pick a storm on the dryline, and watch it spin.

 

[Travis Klanecky]

Now that the NAM is in play, I am really liking the look of things for Thursday afternoon in West Central Kansas. 12z NAM and 12z GFS aren't too far off from each other, although the GFS brings a little more moisture north into Southwest Nebraska. Directional shear looks great and speed shear is looking a little better. I really like areas west of Great Bend and south of Hill City. Being as this is still over 3 days away, I'll hold off on too much excitement, but it looks like the Great Plains are about to be welcomed to Severe Weather season later this week.

 

[Greg Blumberg]

Well, Tim got me interested in this week-long severe weather bonanza after our discussion about Thursday, and now I'm on the Stormtrack thread about to post about my SREF analysis.

Just took a peek at the today's 09 UTC SREF. Things are looking quite good overall for Thursday with the exception of a few minor details. Synoptically, the superposition of high helicity values with the moisture, and the shear is great, however there still seems to be uncertainty in the SREF regarding placement of the shortwave trough and the strength of the surface winds. Both of these, especially the strength of the surface wind have implications regarding both the quality of the moisture and the northward extend of the better moisture.

One thing that I was slightly concerned about when looking at the model was the narrow band of higher 700-500 mb lapse rates stretching all the way from North Dakota down to Mexico. I can't quite figure out why our good lapse rates just disappear, as the SREF doesn't suggest convection is overturning the air. I imagine that this plus the moisture quality uncertainty I mentioned above is giving us questionable CAPE values in model output.

In a synoptic setup that looks as good as this, with no real synoptic fly-in-the-ointment to screw up our chances for good convection, I'd start thinking about mesoscale details i.e. convection that the models might not be picking up on the day before.

As of right now, I can see this being a Wichita Falls/Lawton/Childress chase.

 

[Andy Jackson]

Looking at the last 2 NAM runs 12/18z I'm thinking the northern extent: North Platte, NE to the I-70 may contain the best surface convergence for storm development. From previous runs the last couple of days there seems to be a deficit in the moisture return, but it should be sufficient. The shear is the most impressive of this day with 40+kts at the 500mb and a good helicities at all levels. It's still pretty early, but I'd say this may be the beginning to a chase marathon.

 

[Ben Toms]

I'm generally liking this day to be a big severe weather event, mainly focused across Western Kansas. I've heard people talking about a potential target in the Texas Panhandle as well, but I don't see what is so favorable about the environment further south. It looks like both the NAM and GFS are wanting more of the helicity and moisture pooling to overlap up north in west-central/northwest Kansas. I think we all understand the favorable sides of the set up (being the adequate speed shear, largely curved 0-1km hodographs, and moderate instability) so I'll poke at the disadvantages instead.

The depth and quality of moisture return is becoming a bigger concern for me as the NAM is showing relatively dry 925-850mb air feeding in to our warm sector. I believe this is the cause of the upper 50 dews along our dryline, since a lot of the moisture will be mixing out to these higher elevations.

In addition to that, the general talk has been of a chase marathon with this trough kicking through. We have yet to see what the GFS and Euro will align to, but it's starting to look more like there will be the one big event on Thursday followed by less significant, less tornadic events from Friday through Sunday. The GFS is showing a surface low deepening over NE Colorado and moving quickly to the northeast, reaching Minnesota by Friday afternoon. This means the surface moisture trajectories are southwesterly to at best southerly, which means a bizarrely shaped focus for convergence across the Great Plains and, more importantly, veered surface winds and therefore largely unidirectional shear.

Friday and Saturday are still a long ways off so we will wait to see what actually happens, but for now my confidence only lies in a single day chase on Thursday.

 

[Derek Weston]

Could be a pretty good day. Borderline day before the day sort of setup. (but one of those that might be the better day due to stronger directional sheer)

Timing of the arrival of upper level energy is my biggest concern. 00z NAM knocks it back a bit. (previously had been a nice shortwave over most of W KS)

I'd like the surface winds to be a bit stronger and more backed. Not that perpendicular with the DL. I think they're good enough to get it done, though.

I'd favor a slightly more northerly target more near the triple point. Storms popping off the DL and moving NNE into more favorable helicity will have a better shot.

Storm motions are quite favorable for this early in the season... that's a plus.

All in all... solid -- though not great -- looking event at 72hr out. (with my biggest worry being how quickly the trough swings in... if we've got our upper level support in good time I think it'll come together)

Agree with Ben that the ensuing days have issues with veered low level shear leading to some less than desirable hodographs. Wouldn't bat an eye on those sort of hodos if they were out east of the gulf... but in the plains... a bit concerning.
(might be a better play to go up north along the WF those days... but I'll leave that for another thread)

 

[Chris Wilburn]

Looking at the 06z NAM here at work. The area I would favor is from Russell, KS and points to the north and northwest of there. This area has a nice backing of the surface winds just east and northeast of the surface low creating some very nice directional shear. Moisture and instability will not be in question which is nice early in the season. There are two main issues that may come into play. There isn't much speed shear (if any) from 500mb up. Also, any slow down of the trough will leave the best 500mb winds just out west away from the dryline. I don't see these being an issue, but something to keep an eye on. The 40kt 500mb winds will allow for nice storm speeds which is a plus for this time of the year. All in all it looks like a solid chase day to me. I was hoping OK would be in play for this setup, but the models seem to be hinting at some drier air at 850mb creating less than desirable dewpoints. Also, the 500mb winds are lacking in the area as the trough hasn't quite entered this area yet as opposed to areas to the north in KS.

 

[J Trueblood]

If I were anywhere remotely close to the Midwest, I'd probably start somewhere near Kinsey/Larned/Great Bend and then maybe jump north if I need to. But I'd want to start out close to the surface low/warm front intersection. The crossover between shear and CAPE also looks best here, with DP in the 60s. Helicity is a little bit better just off to the Northeast, but anything that fires in this area might make it's way into that environment. We'll see. Timing could also be an issue, as Derek mentioned.

 

[Andrew Stoller]

I'm seeing a potential problem with this setup, and that is the degree of surface heating and airmass recovery ahead of/to the east of the dryline. The instability axis at 00z Friday is fairly narrow and CIN fills in per both the NAM and GFS. Temperatures drop the further east you go. The window of opportunity for surface based convection to mature and organize is very narrow in the more traditional dryline area south of the de facto warm front that will be draped along the KS/NE border. It looks like fog and low clouds from the strong moisture advection could limit the overall potential Thursday.

 

[Ben Toms]

I'm not too concerned about the warm sector being too narrow - we have about 100 miles of consistent high 60 temperatures, and I wouldn't really want much more than that with the dews we'll have in place. The thing that has been worrying me today is the fact that it does appear that there will be a stratus deck over most of the warm sector for most, if not all, of the afternoon which could limit some surface heating. However, the NAM still spits out adequate surface temps so I'm hoping this won't be that big of an issue. The threat for severe weather definitely isn't an overly impressive, wide swath, but I'm content with afternoon supercells running until dark.

 

[Skip Talbot]

Lid Strength Index showing a pretty decent hole opening in the cap across western KS starting at 21z and wide open by 0z. Moisture convergence on the dryline and upper level support from that trough nosing in from the west should be more then enough for storm initiation. The cap quickly fills back in after 0z, but I think that the window is definitely open long enough to establish mature, surface based storms. The more robust updrafts should be able to power through the building inhibition and stay surface while the rest of the convective activity is culled out. We might wind up with some very photogenic, discrete supercells with nice laminar/striated structure at dusk.

Cap opening up by late afternoon and then quickly filling back in later in the evening:
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_57HR.gif
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_60HR.gif
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_63HR.gif

40-50 knots of deep layer shear, a great veering wind profile, and increasing amounts of 1km srh should easily support supercells with a few tornadoes. We'll probably have a sweet spot in the early evening to around dusk where the low level jet is dramatically ramping up, cape and srh combos spike, and mounting inhibition hasn't forced the storms to go elevated. Might not be much of a nocturnal event given the drop off of low level instability and solid capping after dark.

The instability axis is narrow, but it looks easily wide enough to support a narrow line of supercells coming off the dryline. Severe weather coverage will probably be confined to a fairly localized area given that forcing isn't huge, the cap fills back in, and the narrow instability axis. The one thing that could really throw a wrench in this setup is if the system slows down anymore. We'll lose that need moisture advection and upper level support that at this point looks like it's just enough. This doesn't look like an outbreak event, but the balance between just enough and not too much lift and capping often results in some of the best and most photogenic chases.

 

[Seth Edge]

Looks like the new 0z NAM has picked it back up since this morning. Target location as of now is Hays,KS region (nice little dryline bulge). Cap is broken by sunset. More moisture present than previous models. Cape, shear wind profiles, vorticity, vertical velocities look good etc.. looks like a good day with tornados and baseball hail.

-EyesOnStorms.com (follow us on twitter @EyesOnStorms)

 

[Tim Supinie]

I'll not post a thorough and detailed analysis, but I will point out that I did an admittedly crude trajectory analysis from the NAM, and the air that is forecast to end up near Russell, KS, on Friday at 00Z (Thursday evening) is currently near Little Rock, AR, where the dewpoint is currently ~50 F. Take it for what you will. I'm not suggesting that I think the dewpoints will be near 50 F and the NAM is over-doing the dewpoints by 10-15 F. I am suggesting that we might have more moisture problems than the NAM and especially the GFS are letting on.

Things you should know about my method for the trajectory analysis: I only used the surface wind vectors for the analysis, which means that if there's any vertical velocity, that would move the air to a different level and introduce errors. Also, I eyeballed the parcel locations from the NAM forecasts of wind speed and direction using a basic Euler method integration with a 3-hour time step. I need to write a script to do this for me ...

 

[Seth Edge]

If your not suggesting dew points will be below 60 degrees I don't understand your reasoning not to be rude. Are you chasing thursday Tim?

-EyesOnStorms.com (follow us on twitter @EyesOnStorms)