2018-04-30 EVENT: SD/NE/KS/OK/TX

[Dan Robinson]

Figured it was time to start a thread for this day since we've had a number of sub-180 hour model runs on it.

GFS shows a narrow zone of barely-60s dewpoints pooling along a dryline from the TX/OK border into southern South Dakota, with the primary surface low along the SD/NE border at 00z. All while a 60 knot midlevel jet in the midst of broader zone of 30-40kt SW flow moves out over Kansas.

The past few operational runs of the GFS have kept everything but SD capped. An EML around 800mb is shown temporarily eroding some around 00z, but not quite enough to allow storms to initiate south of the SD/NE border. If a storm can go and maintain south of the SD border down into TX/OK, the environment would support supercells. Limiting the tornado potential in these areas is the cap closing back up after 00z along with some apparent mixing causing the dewpoints to take a several-degree hit through the evening.

The current model depictions show the dryline bulge in south-central South Dakota as the most likely environment for daytime tornadoes. Despite weaker midlevel flow, plenty of storms are shown breaking out here, but it could be an early show with the low-level lapse rates peaking out at 21z.

With the main jet streak nosing in, Kansas appears to have the best overall kinematic environment if a storm can go up, but as it's shown right now getting a storm there may be difficult.

Still lots of time for many of these details to change.

 

[Jeff Duda]

Dan's synopsis seems pretty reasonable to me. However, I see some weak mid-level flow at h5 on the 12Z GFS, resulting in some looping hodographs. There's also some VB over the warm front, but the inflection point is somewhat high so that 0-3 km SRH is pretty healthy. Suggests short lived supercells with tornadic potential early before being smothered by their own precip (or being seeded by a neighboring storm).

The precip signal along the dryline over the high plains to the south is on the weak side, likely the result of marginal surface moisture and a seasonally strong cap. It's not beyond saving, though. If moisture verifies a tick or two higher or there is slightly stronger forcing or a weaker cap, then you'll probably be looking at widespread initiation, but with short-lived storms once they move off the dryline.

 

[Taylor Wright]

Looking at the 12z NAM we will be hard pressed to get quality moisture into the best dynamics by Monday afternoon. With off-shore flow progged until Saturday night it also seems pretty reasonable to question the moisture GFS is currently forecasting. That, combined with substantial mixing will probably lead to upwards of 20 degree spreads, with a pretty strong cap immediately to the east of the dryline. The Euro seems to be the more realistic solution with low 50s, just-in-time moisture into the TX/OK panhandles by late afternoon. This can certainly get it done in the panhandles, however at the moment it seems it will be moisture starved until the low fully ejects into the plains on Tuesday. Sure, details can change but I think we need to just start a thread on Tuesday

 

[Royce Sheibal]

Not great, but chase able. SW nebraska is looking friendly. Maybe a little upslope aid going on. panhandle of tx looks like a low chance but high reward spot. I bet a few chasers will be out. Stp is not super high in any areas but the shortwave in the area should help get things going.

 

[Ethan Lang]

I will be out chasing in SW Nebraska. It is right in my back yard and the latest models have been showing a lower and very breakable cap but the one thing that I'm not a fan of is the wind profile. It looks like the shear will be very low end but none the less I will be chasing and searching for the gem. Wish me luck!

 

[Royce Sheibal]

I will be out chasing in SW Nebraska. It is right in my back yard and the latest models have been showing a lower and very breakable cap but the one thing that I'm not a fan of is the wind profile. It looks like the shear will be very low end but none the less I will be chasing and searching for the gem. Wish me luck!

One of the keys to SW Nebraska is paying attention to the location of the quasi-stationary front. Due to the aid of a little upslope it generally forms SW to NE as the front pushes back west during the day. It will create areas of enhanced vorticity and allow for rapid storm development with tors sometimes within 15 minutes from initiation. And not just spin-ups but legit supercells. I rarely get that far out to chase, but it's always fun to watch the satellite and low level velocity radar to predict where that magical surface vorticity is located. And as long as the cells stay within that frontal window you can get a few solid hours of chase on.

 

[Quincy Vagell]

Expect mass chaser convergence today in the eastern portion of the Texas panhandle, even though there are several target areas.

1. The Nebraska play looks to get messy real quick as storms tend to go linear along a cold front. For any locals, this might be a good shot if you don't want to go far, otherwise given meager moisture and deep layer shear vectors largely parallel to the initiating boundary, this doesn't seem like a popular target.

2. Northwestern Kansas and adjacent southwestern Nebraska originally looked like the more intriguing play of the bunch. Near a triple point (low/cold front/dryline), at least isolated convection is likely by mid to late afternoon. Even though storms may remain largely discrete here and show off some structure, moisture will be limited, as dew-points are progged to struggle to reach the mid-50s. Low-level shear may be marginally better than areas to the south, but details below will touch on this point more. The original thought of this play was to avoid chaser convergence farther south and to potentially get into great position for Tuesday, but given an overall lack of low-level moisture and increasing confidence in initiation farther south, this target appears sub-optimal.

3. The most obvious target based on near-term data is the eastern part of the Texas panhandle. Moisture trends this morning are encouraging, with relatively high confidence in dew-points approaching 60F by 00z. Deep layer shear will be favorable for discrete/semi-discrete supercells and low-level shear is progged to ramp up dramatically by 00-02z, even better than some model progs from last night.

4. Another, perhaps not so obvious target, would be portions of West Texas, south of the Caprock, in the general vicinity of Lubbock. On the southern flank of expected panhandle convection, isolated storm development is also probable. While large scale forcing will be weaker and deep layer shear low-end for supercells, this might be a choice target for someone from the area who wants to avoid the masses or otherwise stay closer to home. It's possible that a tail-end storm may drift off to the east with a vivid structure display before fading away into the night as instability wanes.

Southwestern Kansas/Oklahoma panhandle may be a wildcard target, but convection allowing models have been a bit inconsistent with what happens here. The area is probably displaced a bit too far north from higher quality moisture, but clearly too far south to be considered a triple point play. Don't rule out some noteworthy storm structure if convection is realized in this vicinity, but given greater confidence in chase prospects farther south, this does not seem like a viable option for most.

 

[Warren Faidley]

Target today: Initial, Plainview, Texas. Not chasing today but I would likely pick this area as a starting point. Using SPC mesoscale analysis with HRRR composite reflectivity, it appears everything will hold off until after 22z if the cap is indeed breached. My gut feeling is that at least one storm will pop before 20z between AMA and MAF. There also appears to be a jet streak moving into the area around max heating. Just a safety note: There will likely be a lot of blowing dust along the highways and near storms from the drought.

 

[Jeff Duda]

The 12Z HRRRE (before the website crashed) was pretty stingy with storms in TX. HRRRdev3 is also pretty scant with convection there: