CHASE CASE #1: The 7-Layer Burrito

Jason Politte's recent chase case was great, and certainly with storm season coming up it might be a good time to get up to speed on forecasting techniques.

The following chase case could be anywhere from 1970 to 2005. It is in the late May to mid June time period. This will not be a big bust: at least one supercell will get going. Where will you be? Will you catch the storm?

The Seven-Layer Burrito Chase Case

Upper level charts
200, 250, 300, 500, 700, 850

Surface charts
12Z, 15Z

Surface charts

I'd like to post these tools, but they're not available to me for this particular day.

Thumbnail preview

Indicators such as what upper air station is in operation will not be reliable for helping you pin down the time period... I know these tricks and have taken a few steps to make them unreliable.

Feel free to post your forecast, your tactic for today, or even your own "SPC outlook".

I will give you all the weekend to work on the chase, with possibly an 18Z update by popular request. Enjoy!

I think my target area would be Vernon, TX.
Moisture very good in this region. Not a lot of speed shear but very good directional shear. Td depression low. Storms wouldn't appear to be moving very fast, very chasable.
Interesting case here, given the large domain of data given, as well as the relatively large area that looks nice and juicy...

I am interested in two main locations... The first in central/eastern Texas. There looks to be pretty strong convergence in western Texas with southwest surface winds in southwestern Texas running into low 70 Td airmass a little farther east. The flow at the mid-upper levels, however, is pretty weak. In addition, the MAF sounding shows warm temps that may make for convective bustola.

The second place that looks best to me is western Kansas. It appears that a warm front is located from near DDC to ICT and into southwestern Missouri, and it appears to be moving northward with time. For what it's worth, I place a warm front here based on dewpoints and winds, though the ICT ob makes me a little leary. At any rate, there may be another warm front from near Denver to Rapid City, SD. Southwesterly winds and 30-40 Tds in the norhtwestern TX panhandle indicates an advancing dryline. Skies are partly cloudy in TX/OK panhandles, northern OK, and southwestern KS as well. As far as winds aloft are concerned, it appears that a jet streak will move into the central plains through the day, enhancing deep-layer shear. I would really like to see a DDC sounding (is the lack of a DDC sounding a hint? lol) to judge cap potential...

My target: Larned, KS (as long as surface flow doesn't veer)...
I think the show will be in north-central Kansas and south-central Nebraska, north of the warm front that appears to have developed on the 15z analysis. More easterly winds combined with the ~30 kt flow at 700 mb gives just the right amount of dir and speed shear.

Exact target: Hastings-Hill City-Concordia triangle. Probably around 2030z.
I not sure if these are the correct reasons for selecting this target, but here there are, I like the upper level divergence in NW / N central KS along with the close T / Td. This should lead to a low LCL. This area also appears to be NE of a surface low in E central CO. So I’ll start with Hays, KS and adjust as Tim gives updates.
I think you're on the right track Michael and Kurt (staying far away from TX), but I just left you in Hill City to meet up with Dean in Curtis and continue on to Ogallala, NE, to wait for the action that I hope will initiate near Julesburg, CO, around four p.m.

The upper air action definitely seems to be swinging northeast out of central CO with one or more mesoscale waves. The LBF sounding isn't much help but one can easily imagine Hayes/Hill City low level environment plus some mid-level drying arriving from the southwest during the afternoon. It could look very good indeed then.

Lee side surface low pressure is off the front range near Lamar by 15Z and should continue to move sedately northeast reflecting the upper forcing. This should I hope provide the locus to get the storms spinning toward the ground.

I'm probably totally wrong, but I did stay at a Holiday Inn last night and used some jargon. :)

Ed: Oops! I meant Limon -- not Lamar.
I'd target somewhere around Hays or Stockton in Kansas....where it appears the triple point will be. Further south along the dryline the Altus/Lawton/Wichita Falls area looks interesting as well with mid 70s dewpoints already pooling in that area and stronger winds aloft....but that inversion around 600mb kinda worries me. The area along the warm front and northeast of the surface low seem to be most efficient in cranking out the tubes so northwestern Kansas is the area I'd have my eyes on today.
I think better when doing this in list form...

200 - Jet level analyses show nice diffluent region over srn/swrn NE into KS/OK, along with impressive jet core that should nose into the area of interest during the day
300 - Upper level divergence still impressive
500 - Prefer better midlevel flow over area of wrn KS
700 - Prefer to be at nrn periphery of h7 warm layer, which would suggest nwrn KS
850 - 40 kt LLJ evident vcnty AMA-DDC is impressive, would like to be on cyclonic side

12Z obs - Nice 70+ Tds are tempting in TX, but boundary apparent over nrn KS/srn NE with some moisture pooling looks much better with nicely backed sfc flow
15Z obs - Bit of a Td max in nrn KS, with continued ESErly flow over srn NE

LBF sounding is essentially useless, would LOVE to see DDC. Splitting the difference between the Omaha and Denver temp profiles makes for a nice looking profile vcnty swrn NE.

Best juxtaposition of dynamic forcing with thermodynamic support is sending me to McCook, NE, ready to blast off should Tim's later updates prove to me that I'm totally out to lunch.
Well, we don't have to worry about moisture availability. Denver has a couple thousand feet of moisture, mid 60 dewpoints have made it to Amarillo and there are near 80 dewpoints along the gulf coast. Looking at the soundings in the southern plains it appears that the moisture at amarillo is not deep enought to hold it on the cap rock. The other soundings accross the southern plains are severely capped with 700 mb temps approaching 14 C. That said, it appears to me that the action on this day will be farther north in Kansas and Nebraska.

The atmosphere across Kansas and Nebraska appears to be recovering from overnight convection which was triggered by a lead shortwave that is located in Northern South Dakata at 12z. The stabilizing affects of the overnight convection should limit the north and eastern extent of any severe surface based convection.

Morning soundings from Denver and Amarillo indicate steep midlevel lapse rates that should advect northeastward during the day and combine with plentiful low level moisture to produce very high to extreme instability. Morning upper air charts indicate a strong shortwave trough over western New Mexico. This shortwave is associated with a 60knt 500mb wind max and a sharp thermal trough. This trough should lift out to the NE during the day and help to advance the dryline which can already be seen surging eastward through SE and EC Colorado. As the lee cyclone deepens in response to the upper air disturbance the low level jet should re-establish itself across western Kansas. This will act to enhance shear profiles in Kansas and Nebraska.

I expect storms to initiate somewhere between Medicine Lodge and Hill City and spread northward into Nebraska with time. The greatest tornado potential should be along the warm front which I believe will be located near the Kansas/Nebraska state line by late afternoon.

I would expect a moderate risk area for central and southern Nebraska and for Kansas north of I70. I would position my self somewhere near Russell, KS.

It was fun trying to figure this out using only surface and upper air data, helps me to appreciate the 1km visible loups that are so readily accessible.
Virtual Chase

I love seeing 70's Td's in KS, it's been a while... My target is Garden City, KS. Probably good synoptically driven dryline buldge, on the cold side of the jet, juicy air, and approaching shortwave. I wouldn't expect a big tornado event given the weak low-mid level flow.
Gene and I are recovering from a particularly bad 7-layer burrito lunch in Colby, KS with our trusted tub of Pepto Bismol. No matter - it's early - plenty of time for those guts to find some karma....

We do have a forecast - and we do not know what date this is. Our winds are stiffly streaming across the pristine northwestern Kansas landscape, and we are anticipating what may happen by 6pm.

Mr. Politte promised us he'd be in touch but we haven't heard from him since he left from Conway, AR on his zombie-drive to catch this system up here. :wink:


EDIT: Adam - be careful!! Remember that we have only seen a snapshot of upper-air obs taken in the morning of this date. Try to anticipate.......the atmosphere will not be the same come 0Z as it is now at 9.00am.....
My totally novice forecasting skills can see me setting up shop near Altus, OK around 2 or so, waiting to see where the storms start to pop. Then I will question myself, should I have started in Woodward? The internal non-assurance will continue until something fires. :lol:
After lunch in North Platte we're still going to head west down the road to Ogallala. Dp upstream, i.e. Imperial and McCook, are pushing into the mid-upper 60s with the hoped for clearing mid-level. Nicely backed winds, a T-Td of 10-15F, upper energy juicing up the surface low and dry punch to the southwest, and throw in 3,500' elevation. What's wrong with this picture?
Target: McCook, NE

The warm front in C/N KS looks like the best game to play, IMO. S/w trough moving out from the west is poised to initiate storms in the central plains. Also, I like the fact that this area is on the nose of a 40 kt LLJ.


EDIT: I actually think this was a big tornado day...thermodynamics were spectacular, good baroclinic boundary was in play, and the low-level shear was probably spectacular along the warm front.
After reviewing the 18z data, I’m heading NW from Hays towards Hill City and will look for initiation to the NW. I think Storms will build back towards the SW, so will look for a tail end charley.
After a check of the 18 z surface obs I feel my forecast is still on target. Warm front has lifted to near I 70 as expected. My target was Russell, I feel I am slightly too far south now and I would begin heading north toward the Nebraska state line. I also note that an area of strong moisture convergence has set up shop over the SE Texas panhandle and this same area will be in the RR quadrant of the 60 knt jet streak as it emerges into the plains. However it is my experience that the LF tends to go first. The LF should be coincident with the moist tongue, near 70 F DP, that have surged to near the Nebraska state line south of Lexington. This is the area I would be attacking where high instability and strong shear, due to backed winds along the warm front will produce conditions highly favorable for supercells and potential tornadoes given low LCL's.
I'm still feeling confident in my target of McCook, NE, but I am watching 1km vis pix and surrounding skies watching for first signs of initiation lest it take place just to my south and cut me off.

I'm really liking this boundary.

edit: It's a target, not a targer...duh.
Excellent job, Tim! Your cases are always very well done.

Originally posted by Karen Rhoden

Mr. Politte promised us he'd be in touch but we haven't heard from him since he left from Conway, AR on his zombie-drive to catch this system up here. :wink:

You know me all too well, Karen. :lol: I might consider staying away from those particularly bad convenience store burritos on a day like this though.

I've always been a sucker for those warm front/dryline intersections, and I'll be heading somewhere in the Norton, KS to Arapahoe, NE vicinity to await initiation. I'll have some decent road options there and can always bump north if need be. :)

Back to preparing for a real chase tomorrow.

Without having read other's replies yet I'd be headed toward the area starting to clear just to the west of Hays, KS. The upper level winds are well sheared here and the surface winds are backing nicely, which I like. I'd be headed a little further north to the east surface winds if the cloudcover would break up a little more this afternoon. I'm keeping an eye on the visible satellite for that to happen and adjust my route to the Nebraska border if it does.
After looking at the 18z data I'm gonna drift a bit north to Phillipsburg....good west-east route going through there with numerous options to the north if needed.
A little late to get a chance to look this over, but here is my guess(es). Two different areas capture my attention. The first, as has been well noted, is along the warm front / dryline intersection over northern KS. In particular, theta-E nose pointing toward just west of Hill City could certainly draw me toward that region. The down side of this choice is that it appears storm motions would have storms move northward away from the boundary - and toward that horribly cool and drizzly region in Nebraska. Yuk. 18Z update showing a pretty soft dryline up there though, so that is disappointing as well for dryline cells to kick off south of the warm front and then crossing as mature cells. The next best looking region could well be back around Childress. Pressure analysis at 15 Z and 18Z shows a E-W trough in this region intersecting the dryline, along with improving deep layer shear. But, mass convergence looks fairly weak and most of the diffluence was to the north, so the cap might be tough to break despite some indication of a 700 mb cold front sweeping toward the region. I probably would have went with the safer bet for convection in KS without any additional information to go on.