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2019-05-07 EVENT: CO/KS/OK/TX

JamesCaruso

Staff member
Tuesday May 7 looks like a decent chase day in potentially some of the best chasing territory. SPC has the area outlooked in today’s Day 4. Per O6Z Saturday GFS, 90 hours valid at OZ Wednesday May 8, looks like there should be a triple point in northeastern NM / southeastern CO and a warm front draped across central/southern KS. The dryline is somewhat diffuse, and with the axis of the primary mid-level trough still back in AZ, the better 500mb flow will lag the best moisture in the TX portion of the risk area. However, it looks like a lead wave will bring 35 knot 500mb flow into southwest KS atop backed surface winds. This will likely be the case in southeast CO as well, as surface winds wrap into the low and where upper 50’s dews can easily get the job done. The cap is stronger in CO but hopefully elevation/upslope helps overcome that too. The GFS maximizes the supercell composite and EHI in southeast CO. Southwestern KS has some pros also, such as less of a cap and a decent LLJ. I’m not as excited about TX right now due to the diffuse dryline, borderline moisture and mid-level flow lagging to the west. Not an outbreak by any means, but a good “day before the day,” “The Day” maybe being Wednesday the 8th?
 
Not a lot to dislike about this fairly solid setup. Sufficient moisture (for the Caprock), great wind fields, well-timed shortwave arriving at/just after peak heating. The biggest caveat in model-land is the strong signal for widespread convection and/or rapid upscale growth due to too much forcing. Given everything else, I don't think there is reason to believe we wont have 2 or 3 hours of tornado-producing discrete storms on the dryline. I'm planning on being there.
 
Definitely preferring the TX Panhandle now, in contrast to my OP on Saturday. The NAM is consistently bringing the front further south, taking southwest KS out of play. The GFS has still not come into line with this. SPC’s discussion yesterday seemed to prefer the NAM. If I were chasing, I would hedge my bets and go with the TX PH, which has favorable parameters on either of those two models. Dryline is sharper than on both model runs a couple days ago. NAM brings the dryline a little further west, which if it verifies would better co-locate the moist sector under better mid-level flow. Upper air profile not substantially different between the two models, maybe ever so slightly better 500 flow on GFS, also 850 is S, vs SE on NAM so maybe some better low level turning per GFS. Regardless, all signs point to a classic TX PH dryline chase day. Good luck to all who are chasing tomorrow!
 
Agreed with James C. above. The 12Z NAM is showing pockets of better moisture pooling along the dryline through the heart of the Llano Estacado, with some areas of 63F+. There's been consistent progs for deep-layer shear on the order of 35+ knots as the bulk of the trough pushes through eastern New Mexico by 00Z. Those strong, southeasterly 850s will definitely come into play as any storms come off the Llano into the canyonlands. If the boundary layer doesn't de-couple too quickly, I wouldn't be surprised to see an dusk/after-dark tornado threat continue along the Prairie Dog Town Fork and south.

One thing to keep in mind that I'm sure most chasers who have already been out to the TX PH this year know about is the above-average precip in the region means roads going into the canyons along the Caprock may be a bit more dicey than usual after some light rain. Once storms starting coming off the Staked Plains, I'd be mindful of the number of compacted dirt/gravel crossings over the Red River tributaries/Los Lingos Creek that may not be good to go in the dark in the vicinity of a supercell.
 
A multi-model consensus places the greatest risk zone across the Texas panhandle, while there are still some reasons to at least consider other targets.

The 12z HRRR places the surface low somewhat farther north than other guidance, in the northern Texas panhandle. This scenario initiates convection near the triple point and northeastward across the Oklahoma panhandle and southwestern Kansas. While the storm mode may be more messy/clustered up here, note that there will be even more backing of low-level wind fields in vicinity of a quasi-stationary front here.

The 09z SPC SREF also highlights the potential for severe convection as far north as the HRRR does.

Of course, the highest confidence in the most chaseable, more classic, tornado setup appears to be across the Texas panhandle. Here, wind fields strongly favor a supercell storm mode with convective initiation delayed until at least mid to late afternoon. One possible caveat is that it's somewhat unclear how long storms will remain at least semi-discrete, so storm mergers and/or clustering could be an issue toward sunset.

Another area that can't get overlooked is farther south from the Lubbock area, southward to I-20/10 in West Texas. Multiple convection allowing model solutions show a "tail end charlie" supercell around sunset in the general vicinity of Midland. We've seen this several times where the main chase target is close to 35°N/near I-40, but a lone supercell goes bonkers down by I-20 or even I-10 in West Texas. It seems like a bit of a risky play, as convective initiation may hold off until right around 00z, but the odds of a storm being discrete down there are very high.

Any way you slice it, tomorrow looks like a prime chase day in the High Plains. Supercells are likely, possibly over a fairly broad area. Dryline placement is still TBD, whether it's near I-27 (NAM/HREF) or across the eastern panhandle (HRRR/SREF), but dew-points should be up near 60F immediately ahead of the dryline. This combined with favorable wind profiles, more-than-adequate deep layer shear and moderate to strong instability, should be enough to excite most chasers who are able to be out in the field tomorrow.

P.S.
Note that convective evolution Tuesday night could play a big role in Wednesday's severe weather threat, but we'll save more of that discussion for a 5/8/19 thread.
 
Should be a good day with SPC MDT risk in the TX PH. I initially thought this might be the "day before the day," but tomorrow is no longer looking as good with the front pushing south and leaving the best undisturbed air in the less chasing-friendly environs of southeast TX.

For today, possible negatives are the dryline looks somewhat diffuse on the SPC HREF and other models, and 500mb flow looks slightly more meridional than we would like. Maybe a little backing at 300-200, but as has been talked about in other threads that may be high enough up to not be an issue??

I think a position just northeast of the surface low where winds should be better backed would be a plus. AMA should be the epicenter of the action, and if I were chasing today I would choose that as an initial stopping point and adjust from there based on evolving position of the dryline and surface low / triple point. If I had to pick a specific target area now, I would probably head slightly northwest of AMA, not too far, maybe around Boys Ranch or Channing, to be northeast of the surface low. Unfortunately not the best chase terrain over that way, difficult to go due east from there, Lake Meredith gets in the way eventually, and wouldn't want to have to go through the city.

I wouldn't mind being south of AMA's latitude, say Hereford. Think anywhere along Route 385 from Channing to Hereford would be viable but of course adjusting as conditions evolve. Storms will enter the deeper moisture and instability as they move east of AMA's longitude. Unfortunately both the NE and SE quadrants outside of AMA have terrain and road challenges.
 
Following up on multiple targets, you'd think on a MDT risk day more than one produces.

Northern Panhandles should go first, but might get multicellular. SRH will be good on the synoptic boundary.

Other boundary is noted south of if I-40 may go later. HRRR may be keying in on it, but don't take position or hel-tracks as gospel. Watch how that boundary lifts, or not. Cell(s) should be discrete. Also lots of instability that way.

Tough call. Maybe start north? Easier to adjust south, vs the other way. I do like that south boundary though.
 
I'm inclined to agree Jeff, I was nervous about that early activity on the front but it was at least moving NE away from AMA, but recently a SVR-warned cell went up NNW of AMA / E of Channing. Seems too early, lacks upper support and moving into cool air. I suppose my original target just NW-to-SW of AMA could still go in a later round but I like the backed 15kt winds 71/60 at LBB and 71/61 south of there with the dryline sharpening along the TX/NM border.
 
I think the "south" boundary is still between Amarillo and Plainview. Should be enough local SRH on that boundary to overcome 700/850 mb issues the SPC mentions. It's all tornado box anyway.
 
To me, it looked like storm motions were off relative to surface winds in the TX panhandle were at least partly to blame for an underwhelming day.. Storms moving NNE with winds out of the SSE doesn't scream strong low level shear IMO. This could also partly explain why the storm south of Odessa was such a beast for so much longer than anything to the north. This storm was able to move east, more perpendicular to surface winds than the storms to the north. I'm sure there were many other aspects that led to the way the day played out, but the odd storm motions really stuck out to me. These motions were picked up well on CAM models, especially higher res models like the HRRR.
 
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