2024-04-25 EVENT: TX/KS/OK/NE/CO

[Dan Robinson]

A favorable juxtaposition of the left exit region of a southwesterly jet streak over modest instability on Thursday afternoon/evening in association with an ejecting shortwave trough over the southern/central Plains has been indicated by the Euro, GFS and GEFS ensembles over the past few days. This is shown to be the first in a daily series of several such shear/instability overlaps in the Plains and Midwest, any and all of which appear to have significant severe storm potential.

Moisture quality will again be a potential major failure mode for a more robust tornado threat, with the deeper moisture shown well east of the dryline. While details have yet to be resolved, the past few runs of the aforementioned models have favored the Kansas dryline for the most reliable place for convection where shear is favorable for tornadoes, but again, a just-in-time moisture situation is shown. As we've seen many times, whether this concern will be enough to bring the setup's chase quality into question likely won't be resolved until the day before.

 

[Warren Faidley]

I also believe there is enhanced drying along and east of the dryline from mixing of bone dry air over drough-infested ground out west. The models almost never account for this.

 

[gdlewen]

This is one of the reasons why I don't get too excited about model results 2-3 days from a potential event--they can show interesting things that I attribute to the model output being too far removed in time from it's initial conditions.

This is a plot of the 12Z NAM specific humidity output for 4/26/2024 at 00Z--a full 84 hours out:


We get a very sharp dryline with a warm front along a trajectory W central KS through NE OK. (Based mostly on surface variables (pressure, temperature, and specific humidity) and thermal front parameter fields, but also consistent with the gradient in virtual potential temperature and moisture flux convergence analyses.)

Look at the mesohigh analyzed in the TX panhandle. Is this real? Is it the result of prior convection? and if so, when? The NAM STP (not given) shows values of 4-5 near the intersection of the boundary with the dry line, which suggests this area as a potential target for 4/25.

I find it very interesting, and worth the time to check out because it seems so odd, but I bet by Thursday it will be gone.

 

[Brett Roberts]

I'm not sure I can recall ever seeing such a déjà vu setup quite so soon after the original. There are so many parallels to 4/15 that I'm finding it difficult to assess any aspect of 4/25 without immediately drawing that comparison.

So, at the risk of oversimplifying, my baseline expectation is a similar result to 4/15: an excruciating, gut-punch type of daytime cap bust along a dryline that just can't quite sharpen up early enough for CI, thanks to yet another very promising synoptic wave mistimed by 6 hours. The distribution of model QPF solutions at this range is unbelievably similar to 4/15: the major global ensembles generally suggest a low but nonzero probability for meaningful QPF in the warm sector before 00z. So far, the "seasonal trend" has been for the cap to win in that scenario... admittedly using a limited sample size.

The copium perspective would be that low-level moisture, while not spectacular, has somewhat less of a just-in-time element to it this time. There's fairly strong NWP consensus for low 60s dews already in place up to S KS by 18z, whereas on 4/15 we were desperately awaiting a major moisture surge during the 22-01z timeframe. Of course, if the synoptic wave does arrive late, the best moisture likely won't get pulled right up to the dryline... and we could end up again with a diffuse gradient from 50 F right on the dryline to 65 F three counties east.

If I had to describe my expectations probabilistically as of this afternoon, I'd put 65% on a Groundhog Day style repeat of 4/15 vs. a 35% on robust CI by 00-01z. Given CI, the expected environment over the E Panhandles into W/C KS looks reasonably favorable for tornadic supercells, even if it's not quite a slam dunk.

 

[Ben Holcomb]

Capping on the NAM is a bit concerning. It's a little better on the GFS. However, with the drought ongoing at the target and immediately west I would bet the over on capping.

Trying not to put a lot of thought into this yet, but smells like a bust already. I'm liking Wednesday better at this point and I don't really like Wednesday at all.

 

[Warren Faidley]

Another set-up I would chase if I was there, but I'm holding out until May 8+ to maximize my 30 day time frame and funds.

Of the 3-4 potential chase days this coming week, I'd be watching those days with some type of outflow boundary interactions from earlier convection.

 

[Mark Gressman Jr]

From this far out, the NAM and GFS shows some agreement on 2 general areas of interest... one being near Amarillo and north, and the other near Enid. At this point, I think setting up close to Alva, Ok and adjusting as neccessary is the better bet to see something before dark. Moisture and mass convergence along the warm front in this area during the afternoon coincides with 200+ 0-1km SRH and 2000+ CAPE, and the capping isn't as stout as near the dryline. I'm waiting to see how CAMs handle the morning convection when they come into range, but I think this is worth while setup for those within a few hours drive.

 

[Todd Lemery]

I never believed the depth and quality of the moisture would return in time for Thursday’s show. Now it’s only two days out and I’m a believer. Unfortunately I made other plans for Thursday because I was confident of a bust so I’ll have to enjoy the egg on my face if it comes to fruition. The Skew-T grab is from the OKC area.

 

[Matthew Crowther]

Regarding the potential of a cap bust like 4/15, this time at least some of the CAMS have convection at around 00Z, while in the previous setup, it was pretty unanimous that storms would be hard to come by. That, plus the fact that Saturday looks like a possible outbreak day, we will be heading out in that direction early tomorrow.

 

[Jeff House]

Yes I agree Thursday will come together with some daylight. Moisture is kind of JIT and existing outflow may be hard to find. However the ATMO will get primed through the day.

I don't see any squirrelly signatures in the upper levels either. Last week some flies in the ointment were already noted 60-84 hours out. Not so this week.

At this time still 57 hours to go, I like just east of the surface low just south of the WF. If a good cell is right on the WF without crossing it shouldn't be too sloppy. I always like 1-2 into the warm sector, but not too far down the DL.

If the morning rain in eastern Kansas can kick an OFB back into western Kansas, I'd target that OFB intersection with DL.

 

[gdlewen]

The lead up to this event has a distinctly different feel compared to the two previous events, and especially compared to 4/15. We have AC castellanas with virga over Tulsa this afternoon.

​

 

[Mike Smith]

Here is my 2¢ for Thursday and Friday.

[Updated] Thursday and Friday Tornado and Severe Thunderstorm Risk

Thursday and Thursday Night Forecast The yellow area has a significant risk of tornadoes and severe thunderstorms (large hail and damaging t...

www.mikesmithenterprisesblog.com

Both the surface stations in south Texas and the CRP sounding this morning appear to indicate moisture will not be a problem with this one.
The Canadian, UKMET and ECMWF show Thursday will be a "day before the day" situation in the High Plains. The red circle is where I would focus if I had to choose a target this far out.

If things come together, Friday could be a very big day. The question is whether the strong winds at 250 mb get pinched off or continue into the evening.

Saturday (no forecast made yet) is an interesting day. Some random thoughts: There could be a warm front play in KS-OK. Both UKMET and Canadian have a strong surface low between DDC and CDS with a warm front (both models) across NW OK and S Central KS at 1p Saturday. Both models have rich Td's spreading northwest. The 12Z ECMWF at 7pm has rapidly falling pressures in W KS with the warm front across the southern half of the state.

 

[Andy Berrington]

Just FYI the NAM/NAM 3 km almost certainly are going to be wrong with temperatures/thermos in the Panhandle Thursday.

They are both showing an anomalous cold pool lingering into the afternoon due to their poor handling of cloud cover and BL mixing. None of the other guidance suggests this. Will there be cloud cover? Sure. Will it be in the 60s at peak heating? Very likely not.

 

[Mike Smith]

With regard to the Day 3 outlook update, it is the first time I've ever seen SPC explicitly forecast EF-4/5 tornadoes in a Day 3.

In both of these areas, storms are expected to move
east-northeastward off the dryline, encountering strengthening
low-level southerly flow and environment that is increasingly
favorable for tornadoes. Low-level shear will continue to
strengthening into the early evening, and the overall environment
supports the potential for strong to intense tornadoes if a discrete
mode can be maintained.

With that in mind, take a look at the SIGTOR from the 18Z 3km WRF valid at 8pm Friday. I'm not sure I've ever seen higher values. Greensburg was only 4.6. Of course, some of the extreme values from models never verify. However, if supercells can get going in this general environment, it could be a big evening.

At this point, conditions for chasing look good -- but remember, chasing after dark can be extremely dangerous.

 

[Andy Berrington]

The STP in the WeatherModels/Weatherbell graphics is known to run hot due to a different (and erroneous) calculation – I believe using whole atmosphere helicity rather than the appropriate layers – compared to COD/Pivotal/other model sites. Use with caution.