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Severe Weather Threat May 17-19, 2025

Mesoscale Discussion #874

SUMMARY...An increase in strong thunderstorm development appears possible through Noon to 2 PM CDT. This may include evolving supercells, accompanied by a risk for tornadoes, in addition to large hail. Trends are being monitored for the possibility of a severe weather watch.

DISCUSSION...A few cells have begun intensifying within a broader area of convective development now spreading northeast of the I-35 corridor of central Texas. This appears to have been initially supported by large-scale forcing for ascent associated with warm advection based near the 700 mb level, downstream of a mid/upper perturbation within the belt of westerlies emanating from the lower-latitude eastern Pacific. However, the stronger convective cores have probably begun to acquire updraft inflow emanating from the seasonably moist boundary-layer.

The downstream downstream environment remains capped by an elevated mixed layer based near/above 850 mb, but is warming with insolation. Coupled with the forcing for ascent, erosion of the inhibition may allow for a substantive further increase in stronger thunderstorm development during the next several hours. This may include a few intensifying supercells. In the presence of at least modestly enlarging, clockwise curved low-level hodographs, this activity may become accompanied by a risk for tornadoes, in addition to large hail.
 
From Reed


Live emergency update on tornado outbreak expected today across the southern Plains including DFW to OKC to Tulsa to Springfield! This could be one of the more significant #tornado events for the southern Plains in a decade. Stay tuned to severe weather watches and warnings in the moderate risk area.
 
Pbrussell said:
Did anyone grab any good reflectivity scans last evening? There’s velocity scans out the whazoo in the thread but I neglected to snap any of reflectivity. I was in and out of sleep and too busy scratching my head over what was happening to remember to get some
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I took these screenshots when it was north of Preston, KS
 

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Yesterday verified as a moderate risk, as expected, the cloud/fog cover did nothing to deter the development of dryline convection.
1747670509385.png
The storm in Oklahoma after if produced a couple of short lived tornadoes struggled from mid level dry air as the only support it had was nebulous forcing. Which left it with no supporting convection to reinforce it which made it susceptible to dry air entrainment enhanced by the LLJ.

The dryline cells in Kansas and Nebraska were closer to the trough and therefore had a stronger forcing mechanism, and therefore more mini supercells to merge with and keep them going. Inversion layer was weaker in these locations as well looking at the Skew Ts.

I would say the hrrr verified, but every cam model pretty much had the same solution, although they underestimated the strength of the inversion layer in Oklahoma.

Remember, while cloud decks can prevent destabilization, in the face of a strong LLJ, a lot of the stability can be mixed out, which is what happened when night fell. (Important footnote: even where the cloud deck was present, the atmosphere was still plenty unstable, laspe rates were in between 5.5 to 6.5 c/km, which isn’t great, but still sufficient for tornado production).

It also helps that this was dry line convection, not OWS convection, as OWS convection is completely at the mercy of how much destabilization occurs to allow confluence bands to initiate in the first place, and then having to break through the inversion layer.

While dry line convection also needs sufficient destabilization, the forcing from the trough and or convergence along the front negates the total reliance on sufficient destabilization.

Which is why the cells in Kansas were able to put down wedges despite the cloud cover throughout the day, while western Oklahoma completed cleared out and the convection still died.
 
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I will say, confidence in the main storm mode being semi discrete/discrete is increasing quite a bit. Ever since the 10z, semi discrete supercells were being shown and ever since the 12z, discrete supercells are being shown. The 14z and 15z specifically look quite unfun.

Screenshot 2025-05-19 12.07.58 PM.png
15z HRRR

Screenshot 2025-05-19 11.59.47 AM.png
14z HRRR
 

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Ozonelayer said:
I will say, confidence in the main storm mode being semi discrete/discrete is increasing quite a bit. Ever since the 10z, semi discrete supercells were being shown and ever since the 12z, discrete supercells are being shown. The 14z and 15z specifically look quite unfun.

View attachment 42523
15z HRRR

View attachment 42522
14z HRRR
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Getting less messy?
 
Local DFW met sees the highest storm coverage further north of DFW (Red river)

https://x.com/wfaaweather
Pete Delkus
https://x.com/wfaaweather
@wfaaweather


WFAA Weather Alert Day today between 4pm to 8pm. Strong storms are expected this afternoon. The highest coverage of storms will be near the Red River. Up to golf ball size hail, 60-70 mph wind gusts and an isolated tornado are the main threats. #wfaaweather


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